Avi Loeb Medium

Top panel: Images of 3I/ATLAS, taken in the wavelength range of 0.75–5.0 microns between the 8 and 15 of December, 2025. Each image spans 300,00 kilometers on a side. The brightness contours represent 5, 20 and 50 times the background noise; color bars are in mega-Jansky per steradian. The celestial North-and-East directions are shown by black arrows, along with the anti-velocity (dashed-blue) and anti-sun (solid-red) directions. On these large scales, the brightness map of dust and organics was found to be pear-shaped, with an anti-tail elongation in the direction of the Sun. All six other gas plumes were found to be nearly round. Middle panel: Flux spectrophotometry (points), colored by observation date (right color bar) and normalized to equal distances between 3I/ATLAS, the Earth, the Sun (=1 AU). The major spectral emissions of various gas species [CN(0.93microns), H2O(2.7–2.8 microns), Organics(3.2–3.6 microns), CO2(4.2–4.3 microns), and CO(4.7–4.8 microns)] have been color coded. Bottom: Reflectance-Spectrum, given by the flux ratio between 3I/ATLAS and the Sun. The dust spectrum can be described by scattered sunlight and thermal emission. The signature of sub-micron dust particles that would have enhanced the blue color via Rayleigh scattering are absent. Moreover, these small particles would have also been subjected to strong solar radiation-pressure effects and would have formed the standard cometary tail, extending away from the Sun — which is not observed. (Credit: C.M. Lisse et al. 2026)A new paper led by Carey Lisse (accessible here) reports large-scale images of the gas plume around the interstellar object 3I/ATLAS after perihelion, based on data collected last month by the SPHEREx space observatory. The data show enhanced mass loss of dust and gas around 3I/ATLAS. The new images of 3I/ATLAS were taken in the wavelength range of 0.75–5.0 microns between the 8 and 15 of December, 2025. Each image spans 300,00 kilometers on a side. On these large scales, the brightness maps of dust and organics were found to be pear-shaped, with an anti-tail elongation in the direction of the Sun. All six other gas plumes were found to be nearly round. The major gas species were identified as: cyanide (CN, at a wavelength of 0.93 microns), water (H2O, in the wavelength range of 2.7–2.8 microns), Organics (C-H, between 3.2–3.6 microns), carbon-dioxide (CO2, 4.2–4.3 microns), and carbon-monoxide (CO, 4.7–4.8 microns). The CO2 gas-plume continues to extend out to a few hundreds of thousands of kilometers. The dust spectrum can be described as the sum of scattered sunlight and thermal emission. Most notably, the signature of sub-micron dust particles that would have enhanced the blue color via Rayleigh scattering are absent. Moreover, these small particles would have also been subjected to a strong solar radiation-pressure and would have formed the standard cometary tail, extending away from the Sun — which is not observed — as I argued in an essay, posted here on December 25, 2026. Compared to the pre-perihelion data reported from SPHEREx in August 2025, the continuum spectral signature of water-ice absorption has mostly disappeared, replaced by scattered-light plus thermal-emission from organo-silicaceous dust grains, while the water-gas emission is twenty times (!) brighter than it was before perihelion. The new appearance of cyanide (CN) and organic features suggests that these species are contained in the water phases. The new mass loss rate of water (H2O) is 180 kilograms per second, similar to the new mass loss rate of carbon dioxide (CO2), with both being two-thirds of the carbon-monoxide (CO) mass loss rate. The brightness maps suggest that cyanide and organics are sourced from the dust, while the H2O, CO2, and CO-gas originate from a symmetric region centered on the nucleus. The pear-shaped dust anti-tail is consistent with large dust grains. The gas production of 3I/ATLAS had been shown to be dominated by icy fragments in the pre-perihelion imaging of 3I/ATLAS by SPHEREx (as reported here and argued in the paper I co-authored with Eric Keto here). These fragments would have had to be thick, possible more than 10-meters in diameter, in order to preserve deep unprocessed material. Last month, I published a paper here, explaining the large extent of the anti-tail glow towards the Sun in this context. As the authors of the new paper admit, this inference raises a new anomaly concerning 3I/ATLAS. It implies a huge amount of dust mass, because these same large boulders have to provide enough surface area to make the gas plume a hundred times brighter than the nucleus in reflected sunlight. We know that the fragments must be larger than a millimeter, because there is no evidence for a radiation-pressure dominated cometary tail of fine dust. The nature of the scattered sunlight in the glowing halo around 3I/ATLAS has also fundamentally changed around perihelion, from an ice-dominated reflectance spectrum into that of low-albedo dust dominated by bluish light scattering. The SPHEREx data demonstrates once again that science is a learning experience. We need more data to guide us about the proper resolution of the above-mentioned anomaly. We should not be surprised to find out that objects arriving at our cosmic backyard in the inner solar system from the cosmic street of interstellar space, are different from the familiar icy rocks we had seen before. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Illustration of the anti-sunward jet and the opposing anti-tail in the Larson-Sekanina Rotational Gradient filter of a representative image from the Hubble Space Telescope during the month of December 2026. The position angle (PA) of the anti-sunward jet is marked using the standard convention N=0 degrees and E=90 degrees. (Image credit: T. Scarmato and A. Loeb 2026, full paper accessible here)How fast does the interstellar object 3I/ATLAS rotate now? Did its rotation period change during perihelion, when it came closest to the Sun on October 29, 2025? There are two ways to measure the rotation period of 3I/ATLAS. One uses the periodic shift in the orientation of the jet structure launched by 3I/ATLAS as it rotates. The second relies on the periodic modulation of the total brightness of 3I/ATLAS, including the glowing halo of coma and jets around it. In a new paper that I co-authored with Toni Scarmato (accessible here), we measured the rotation period of 3I/ATLAS after perihelion in both ways. First, we measured the position angle of the anti-sunward jet on the sky at multiple times by applying the Larson-Sekanina Rotational Gradient filter to Hubble Space Telescope images between November 20, 2025 and December 27, 2025. Second, we analyzed brightness evolution between December 9 and 22, 2025 using data from the 0.25-meter telescope MPC L92 in Calabria, Italy. Images of 3I/ATLAS from January 13, 2026 in three formats: gray scale brightness map (left), false colors (middle row) and processing through the Larson-Sekanina Rotational Gradient Filter which removes the circularly symmetric glow (right). The filtered images on the right side show a prominent anti-tail jet towards the direction of the Sun on the lower-left. As 3I/ATLAS approaches opposition relative to the Sun with the Earth in the middle, on January 22, 2026 (predicted here), the anti-sunward jet will disappear from view and the anti-tail jet will be pointing at us. (Image credit: T. Scarmato)We have found that the periodic wobbles of the jet position-angle by +/-20 degrees occur over a period of 7.20 (+/- 0.05) hours. Independently, the periodic variations in brightness by +/-30 percent yield a period of 7.136 (+/- 0.001) hours. The two periods differ slightly, but the small difference is plausibly attributable to systematics and aliasing. The combined data supports a post-perihelion rotation period of about 7.1 hours, triggering a periodic precession of the jet structure around the rotation axis of 3I/ATLAS. The top panel shows the position angle of the anti-sunward jet of 3I/ATLAS as a function of phase after folding its evolution over a period of 7.2 hours. The bottom panel shows the periodic variability of the magnitude (proportional to logarithm of the brightness) of 3I/ATLAS as a function of phase after folding its evolution over a period of 7.136 hours. (Credit: T. Scarmato and A. Loeb 2026, full paper accessible here)Since the jet is precessing around the rotation axis, we associate its average position angle value of 270 (+/-3) degrees with the rotation axis. Given that the Sun-3I/ATLAS axis is at 290 degrees, we infer that the rotation axis of 3I/ATLAS is aligned with the Sun-3I/ATLAS axis to within 20 degrees. This surprising alignment needs to be explained, as the rotation axis was set in interstellar space, far from the Sun. Based on the first image of 3I/ATLAS taken by the Hubble Space Telescope on July 21, 2025 (as reported here), less than a percent of the scattered sunlight originates from the surface of its nucleus. The mass loss rate increased significantly near perihelion. This means that the modulation of the post-perihelion flux by tens of percent can only originate from the glow surrounding the nucleus. As the nucleus rotates, the dominant outflow direction sweeps around the rotation axis as a result of the precession of the jet, which in turn modulates: (i) the column density of dust along the line-of-sight; (ii) the distribution of dust within the photometric aperture; and (iii) the effective scattering phase-function of the dust particles. Changes in jet orientation therefore produce periodic variations in the observed flux of scattered sunlight. The resulting “heartbeat variability” — by which the jets pump dust and gas into the coma like a heart pumping blood through veins into a body — was suggested in an essay that I wrote on November 30, 2025 here. Prior to that, it was argued incorrectly (as mentioned here) that the brightness variations stem from changes in the reflected sunlight from the surface of a rotating nucleus. In reality, the underlying rotational state of the nucleus can manifest differently in brightness and in jet position angle. If the jet direction is tied to a fixed active area on the rotating nucleus, then the jet orientation would exhibit periodic shifts, and the integrated brightness would vary periodically as the jet alternately points closer to, or farther from, the line-of-sight. Thus, if the jet direction undergoes precession around the rotation axis (e.g., due to a high-latitude source region and changing illumination geometry), the brightness variability period would correspond to the jet-orientation cycle rather than to the nucleus shape as it reflects sunlight. The observed periodicity should be regarded as a jet-driven modulation that traces the rotational state through the jet orientation, rather than a direct measurement of reflected light from the nucleus itself. Our inferred value for the jet precession period after perihelion of 7.2 (+/-0.05) hours is consistent with the value measured for the periodic jet precession before perihelion of 7.74 (+/-0.35) hours (as reported here). However, it is shorter by a factor of about 2.3 than the rotation period of about 16–17 hours inferred from the brightness variability before perihelion (as reported here and here). The difference in brightness periodicity might have resulted from a change in the number of jets or active spots — likely induced by the perihelion passage of 3I/ATLAS. For example, the perihelion passage could have doubled the frequency by which the coma flux is modulated by jets since the rotation axis is nearly aligned with the Sun-3I/ATLAS axis. Whereas only one of the rotation poles was illuminated by the Sun before perihelion, the second rotation pole was illuminated by the Sun after perihelion, potentially triggering two active jets — which are also viewed from a different angle after perihelion. Altogether, the new data indicates that the periodic wobble of the jet around the rotation axis did not change during perihelion. The alignment of the rotation axis of 3I/ATLAS to within 10–20 degrees with the direction of the Sun at large distances is anomalous, as it has only a probability of 1.5–6% for occurring at random in interstellar space. 3I/ATLAS will be within 0.69 degrees from perfect opposition relative to the Sun with the Earth situated in the middle on January 22, 2026 (as described in the other new paper that I co-authored here). On that date, the anti-sunward jet will nearly disappear from view and the sunward anti-tail jet will be pointing at us. *** Speaking about period keeping, let me close this essay with a general note about extraterrestrial time keeping, which recently appeared in the news also in the context of synchronizing clocks on the Moon relative to Earth. According to Albert Einstein’s General Theory of Relativity, time progresses slower in the presence of stronger gravity — which manifests as curvature of spacetime. The extreme manifestation of gravitational time-dilation can be found near the event horizon of a black hole, where time slows down to a halt from the vantage point of a distant observer. If we were to video-record astronauts falling into a black hole, we would find their final image to be frozen at the instant when they crossed the event horizon. The reason is simple: no information can escape from inside the horizon, so their last image stays forever frozen for distant observers. For the same reason, time is ticking slower on Earth than on the Moon as the lunar gravitational potential well is shallower than that of Earth. The gravitational time dilation is larger than the net time dilation due to the second-order Doppler effect, which is of order the square of the velocity of the Moon around Earth normalized by the speed of light. The slowing in the progression of time near Earth is a mild version of the black hole extreme. Time on the Moon progresses faster than on Earth by approximately 56–59 microseconds (millionths of a second) per day. The fractional drift is about 0.66 parts per billion faster than Earth time. Over 46.5 years, the drift amounts to one second. Precise timekeeping is important for maintaining synchronous operation of electronic equipment on the Moon. If synchronicity slips out of control, we would not be able to keep a proper record of events or communication protocols among computers and other electronic equipment on the Moon and on Earth. Time is ticking even faster on spacecraft than on the surface of the Moon. But irrespective of where they are in the Solar system, all astronauts and earthlings are embedded inside the gravitational potential well of the Milky-Way galaxy. This adds a Galactic fractional slowdown of about a part in a million, much larger than that induced by gravity on Earth. Over a lifespan of 100 years, we (along with all our Milky-Way neighbors) age slower by 53 minutes (!) than average cosmic residents in intergalactic space. Thanks to that, we can observe the Universe during each century for nearly an hour longer than our intergalactic counterparts. *** Earlier today, I received the following uplifting email, titled “Thank you for making me more curious”: “As a Microbiology lecturer at a Massachusetts Community College, I am usually looking down the tube of a microscope. You have inspired me to turn my gaze toward the stars and look with humble curiosity to the heavens. Thank you for your open-minded scientific questioning. I’ve been following your Medium.com feed, news interviews, and I read Extraterrestrial. Great work. Best, Sage Franetovich Professor of Biology Greenfield Community College Greenfield, MA” ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

The angle between the Sun-Earth axis and the Sun-3I/Atlas axis in degrees, as a function of date. (Credit: M. Barbieri and A. Loeb; full paper accessible here)In a new research note that I co-authored with Mauro Barbieri, we point out that on 22 January 2026, the interstellar object 3I/ATLAS will align to within an exceptionally small angle of 0.69 degrees, with the Earth-Sun axis. This rare alignment provides unique circumstances for measuring a novel effect called `the opposition surge’ for the dust shed by 3I/ATLAS. We characterize the alignment geometry, outline key scientific opportunities, and provide observational requirements for data collection. Observations before and after the alignment time offer an unprecedented opportunity which may not repeat for decades, for characterizing the albedo, structure, and composition of interstellar matter. Our paper is accessible here. Let us start with some background. On July 1 2025, the Asteroid Terrestrial-impact Last Alert System (ATLAS) discovered the interstellar object 3I/Atlas. Follow-up, as well as pre-discovery, observations validated its hyperbolic orbit with eccentricity e ≈ 6.139 and perihelion distance of q ≈ 1.356AU, confirming its interstellar origin. Its interstellar velocity relative to the Sun of 57.7 kilometers per second is large in comparison to two other documented interstellar objects, 1I/‘Oumuamua with 26.4 kilometers per second and 2I/Borisov with 32.3 kilometers per second. Interstellar objects provide unique opportunities for studying materials from other stellar systems, including extraterrestrial technologies. However, 1I/’Oumuamua did not display traces of gas or dust around it and 2I/Borisov was only observed at phase angles relative to the Sun-Earth axis of α > 16 degrees and never near opposition. Our paper points out that 3I/ATLAS will reach an unprecedented near-opposition alignment on 22 January, 2026 at 13:00 UTC. At that rare time, Earth will pass nearly between the Sun and 3I/ATLAS. The phase angle α between the Sun- 3I/ATLAS axis and the Sun-Earth axis, will reach a value of 0.69 degrees. Unlike typical cometary opposition geometries which often last for hours, 3I/ATLAS will maintain α < 2 degrees for approximately one week, between 19–26 of January, 2026. Based on its JPL Horizons trajectory, 3I/ATLAS will be on January 22, 2026 at a distance of r = 3.33 AU from the Sun (where 1AU-=Earth-Sun separation), a distance of ∆ ≈ 2.35 AU from Earth, and have a V-band magnitude of V ≈ 16.7 mag. The phase angle of 3I/ATLAS will remain small in subsequent years as it recedes from the Sun, but its magnitude will be fainter — requiring larger telescope apertures. For example, in January 2027: α ≈ 1.4 degrees, r ≈ 16 AU, V ≈ 24 mag, and in January 2028: α≈0.8 degrees, r≈28AU, V ≈25mag. At phase angles α < 10 degrees, most Solar System bodies show a substantial brightness increase, called `the opposition surge’. This surge arises from two physical effects: • Shadow-hiding: (α > 2 degrees): When the Sun, object, and observer are nearly aligned, shadows cast by dust particles are hidden behind the particles. This eliminates dark areas, increasing the object’s brightness. • Coherent backscatter: (α < 2 degrees): At very small angles, light traveling on reciprocal paths through a dusty medium interferes constructively, creating a narrow brightness spike as a consequence of quantum mechanics. The surge amplitude is strongly influenced by the scattering albedo of dust grains ω0, as well as by the grain structure and packing. The angular-width of the surge constrains grain packing, as compact particles show narrow surges with half-width of order a few degrees, while fluffy fractal aggregates show broad surges with half-width of order tens of degrees. As of now, only one comet has a well measured opposition surge: 67P/Churyumov–Gerasimenko (as reported here). The surge was observed from the Rosetta spacecraft at α = 1.3 to 5 degrees, yielding ∆m = 0.15 ± 0.02 mag and a very dark albedo with ω0 = 0.034 ± 0.007. For most of the solar system comets, the opposition surge measurements are unavailable or either incomplete because of a large value for the minimum α. The previous interstellar comet 2I/Borisov was never observed below α = 16 degrees, far outside the opposition surge regime. Cometary dust is processed through its parent proto-planetary disk, and so its microphysical structure might be different from interstellar dust. The opposition surge amplitude and width of 3I/ATLAS could address the following questions: · Composition: Is the dust shed by 3I/ATLAS dominated by carbonaceous material (low albedo, ω0 ∼ 0.03) or does it retain significant ice fragments (high albedo, ω0 ∼ 0.1–0.3), as suggested in my papers with Eric Keto (here and here) based on its extended anti-tail? · Grain Structure: Are the grains compact (thermally processed) or fluffy fractal aggregates (pristine molecular cloud material)? The unique near-opposition geometry of 3I/ATLAS on 22 January, 2026 provides a narrow but well-defined observational window. To maximize the scientific return of community observations, we recommend the following: · Temporal coverage: Observations should be obtained over a time span of at least ± 4 days around 22 January 2026, when the phase angle remains below 2 degrees. This extended coverage allows separation of phase-angle effects from intrinsic activity variability. · Photometry: High-precision relative photometry (≲0.03 mag per data point) is required to detect and characterize the nonlinear phase dependence associated with the opposition surge. Consistent aperture sizes and background subtraction methods should be used throughout the observing campaign. · Multi-band observations: Photometry in at least three broadband filters (e.g., BV R, V RI, gri, riz) would be of great value. The wavelength dependence of the phase curve provides critical diagnostics to distinguish between the shadow hiding and coherent backscattering mechanisms. · Polarimetry: Linear polarimetric measurements near minimum phase angle would offer a powerful and independent constraint on dust grain structure and multiple scattering effects. Even sparse polarimetric sampling would significantly enhance the interpretation of photometric data. · Aperture considerations: Given the expected brightness (V ∼ 16.5–17 mag near opposition), telescopes with apertures larger than 1 meter are well suited for precise photometry, whereas larger apertures are required for polarimetric measurements. Coordinated observations from multiple sites are needed to improve temporal sampling and to mitigate weather-related data gaps. Even partial datasets will contribute meaningfully to constraining the phase-angle behavior of the rare alignment of 3I/ATLAS with the Earth-Sun axis. Here’s hoping that many observers with access to suitable telescopes will take advantage of the extraordinary fortune that we are about to have through the rare alignment of 3I/ATLAS with the Sun-Earth direction. Related data can help decipher the nature of the anti-tail jet of 3I/ATLAS and resolve other anomalies — such as its unprecedented polarization properties (as reported here). ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

The Near Transits of the Inner Planets Across the Face of the Sun from the Vantage Point of 3I/ATLASThe expected trajectory of 3I/ATLAS will nearly align with a transit of the Earth across the face of the Sun on January 22, 2026. (Image credit: NASA/JPL Horizons)When a planet transits in front of the disk of its host star, its blocks some of the starlight and reduces slightly the brightness of the star. The tiny fraction of starlight passing through the atmosphere of the planet allows to measure the atmospheric composition. In particular, the transit of the Earth in front of the Sun produces a dimming of only 0.008 percent for a distant observer that is aligned with the Sun-Earth axis. Nevertheless, a high-quality spectrograph on a purposely designed space telescope could identify the spectral fingerprints of oxygen and methane molecules as biological signatures of terrestrial life, as well as tetrafluoromethane (CF4) and trichlorofluoromethane (CCl3F) as technological-signatures of industrial pollution. In 2014, I tasked my undergraduate student then, Henry Lin — who currently serves as an assistant professor at the Princeton’s Physics department, to calculate the detectability of the spectral fingerprints of industrial pollution in exoplanet atmospheres. Our paper, published here, identified detectable spectroscopic features of chlorofluorocarbons (CFCs) in planetary atmospheres. An interested observer passing through the ecliptic plane of the Solar system could employ the transit method to monitor the evolving biological and technological conditions on Earth in real time. We must keep this possibility in mind while monitoring anomalous interstellar objects as candidates for technological probes which were sent into the solar system by extraterrestrial civilizations. The ideal path for transit-focused probes are retrograde trajectories (opposite to the motion of the Earth) that are aligned with the ecliptic plane of the Earth around the Sun, where they will be able to monitor as many transits of Earth or other solar-system planets throughout their journeys. As it turns out, we have right now a suspicious interstellar visitor which follows a retrograde orbit which is aligned to within 4.9 degrees with the ecliptic plane. Even though this interstellar object 3I/ATLAS displays many anomalies (as listed here), the official view is that 3I/ATLAS is a comet of natural origin. However, if it happened to be a technological probe equipped with a spectrograph — it could have used its journey to observe transits of the Sun by all the inner solar system planets: Mars + Mercury, Venus and Earth on October 2, 2025; November 4, 2025; and January 22, 2026, respectively. Unfortunately, the actual orbital inclinations by several degrees of 3I/ATLAS and the planets relative to the ecliptic plane, make all these transits except Venus a near miss from the precise vantage point of 3I/ATLAS as it crosses the inner solar system. If 3I/ATLAS had been perfectly aligned with the ecliptic plane, then it would have detected biological markers such as oxygen and methane, when it entered the outskirts of the Oort Cloud at 100,000 times the Earth-Sun separation (AU) some 8,000 years ago. More recently, in 1950 — when Enrico Fermi had asked the question: “Where is everybody?”, 3I/ATLAS had been at a distance of about 1,000 AU where it could have detected industrial pollution in the Earth’s atmosphere — indicating that our planet went through an industrial revolution. In 1977, when the “Wow! Signal” was detected, 3I/ATLAS was at a distance of about 600 AU from Earth. And on January 22, 2026 when the Earth will nearly align with the Sun from its vantage point, 3I/ATLAS will be at a small distance of only 2.35 AU from Earth. The trajectory of 3I/ATLAS nearly aligned with transits of Mars+Mercury (top) and Venus (bottom) in front of the face of the Sun on October 2 and November 4, 2025, respectively. (Image credit: NASA/JPL Horizons)The NSF-DOE Rubin Observatory in Chile is expected to harvest several dozens of interstellar objects over the next decade. Given the near misses of 3I/ATLAS, we should check if any of them aligns precisely with transits of planets as they approach the Sun. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Image of 3I/ATLAS, taken on January 7th, 2026 by the Hubble Space Telescope (top panel), and processed through the Larson-Sekanina rotational gradient filter (bottom panel). The bottom panel shows a triple jet structure with a prominent anti-tail jet in the direction of the Sun, towards the lower left corner of the image. The anti-tail extends to a scale of order the Earth-Moon separation. (Image credit: Toni Scarmato, based on data released by NASA/ESA/STScI here)When the interstellar object 3I/ATLAS was first imaged by the Hubble Space Telescope on July 21st, 2025, it became evident that the glowing halo of light around it extends by an extra factor of ~2 towards the Sun. Given that the observing line-of-sight was only 10 degrees away from the sunward direction at that time, this implied that the actual extended structure is of a jet that is 1/sin(10 degrees)=5.8 times more elongated than observed in the projected image, namely ~11.6 times longer than it is wide. But the most surprising fact about this jet is that it is oriented in the sunward direction. Usually, the elongated feature around comets is oriented away from the Sun. The physical reason is simple: the solar-wind push on gas and the solar radiation push on dust create the appearance of a cometary tail extending away from the Sun relative to the nucleus. But 3I/ATLAS exhibits a physical anti-tail that is definitely not a visual illusion due to a projection effect created by a special viewing angle. Intrigued by this unusual phenomenon, I wrote three papers (posted here, here and here), attempting to explain the physics behind it. When the first paper in this series, co-authored with my colleague Dr. Eric Keto, was submitted for publication in “The Astrophysical Journal Letters,” we were informed by the editor that the paper will not be sent for review because: “I believe that your results would be of rather limited interest to the astrophysics research community as a whole.” Disappointed by this response, we submitted the paper to the competing journal “Monthly Notices of the Royal Astronomical Society”, where it was accepted for publication after a very favorable referee report. This experience shows how subjective the editorial and peer-review process is in academia. By now, it is clear that the anti-tail jet of 3I/ATLAs is one of its major anomalies, because it is clearly observed in post-perihelion images taken from different perspectives during the past couple of months. These images show (as I described most recently here, here and here) a prominent anti-tail jet that extends out to 400,000 kilometers from the nucleus of 3I/ATLAS towards the Sun. The anti-tail is evident in the latest Hubble image, taken on January 7th, 2026. The application of a Larson-Sekanina rotational gradient filter that removes the circularly symmetric glow around the nucleus of 3I/ATLAS reveals a triple jet structure with a major tightly-collimated anti-tail jet towards the Sun. The two minor jets are equally separated in angle from each other and the anti-tail, and are not oriented away from the Sun — as expected from a familiar cometary tail. As inferred from the first Hubble image on July 21, 2025, the anti-tail jet is tightly collimated and an order of magnitude longer than it is wide. The tight collimation and the prominence of the anti-tail relative to any tail feature, are surprising given that the anti-tail jet goes through the countering pressure of the solar wind and the solar radiation. Given that, I beg to differ with the above-mentioned editorial opinion. The physics responsible for this remarkable anti-tail jet is not “of rather limited interest to the astrophysics research community”. From the wobble of the anti-tail jet around the rotation axis when 3I/ATLAS was approaching the Sun (as reported here), it became clear that its rotation axis is pointed at the Sun to within 7 degrees at large distances. This constitutes another unexplained anomaly on top of the alignment of the trajectory of 3I/ATLAS with the ecliptic plane, each with sub-percent probability — making their combined geometry unlikely at a level below 0.0001. NASA officials did not mention these geometric anomalies at their press conference about 3I/ATLAS on November 19, 2025, when they concluded that 3I/ATLAs behaves like a regular comet. Obviously, if one ignores the unexplained anomalies of 3I/ATLAS, one would conclude that there is nothing surprising about it. The easiest way to argue that we fully understand something is by ignoring what we do not understand about it. However, the foundation of science is the humility to learn, not the arrogance of expertise. What is the point of pursuing science if practitioners claim that they understand nature based on past knowledge even when data shows that they might be missing something. Our ability to learn something new is limited by our willingness to admit what we are missing. Anomalous data should not be “of rather limited interest to the astrophysics research community”, but instead of great interest for the astrophysics research community. Science is fun as long as we treat it as a learning experience. Curiosity is a genuine trait of a beginner’s mind. My hope is that the next generation of scientists will do better than my generation in revolutionizing our perception of our cosmic neighborhood. The Universe will not appear a lonely place if we find residents in our cosmic street. Finding these residents would update the priorities of humanity beyond Earth. In a WORLD.MINDS forum led by the brilliant Rolf Dobelli yesterday, I asked the historian Sir Niall Ferguson: “Could science bring humanity to pursue a vastly better future than its past?” Niall responded that science is not separate from power politics. He argued that throughout history, humans evolved as fighters and killers. The 20th century saw extraordinary scientific breakthroughs and unprecedented mass killings. Niall suggested that these facts are not unrelated. Niall is right about our past. But I am hopeful that an encounter with a more accomplished extraterrestrial civilization will make our future better, as we receive our inspiration from the stars. As Oscar Wilde noted: “We are all in the gutter, but some of us are looking at the stars.” For that reason, when we observe interstellar objects in our backyard, we should not treat their anomalies as being “of rather limited interest.” Instead, let us focus on understanding the anomalies of 3I/ATLAS (as listed here), starting with its anti-tail jet. This visitor to our backyard is not a regular street cat since a tail appears to be emerging from its forehead. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Expected trajectory of 3I/ATLAS, as of January 7, 2025. (Image credit: NASA/JPL Horizons)About 8,000 years after entering the Oort Cloud of the solar system at a distance of 100,000 times the Earth-Sun separation, the interstellar object 3I/ATLAS embarks on the second half of its trip, now away from the Sun and towards Jupiter. According to its forecasted gravitational trajectory and including its non-gravitational acceleration, 3I/ATLAS is expected to arrive on March 17, 2026 to within 30.46 million kilometers from Jupiter’s irregular moon Eupheme. A day earlier, 3I/ATLAS will be within 53.61 million kilometers from Jupiter, surprisingly close to Jupiter’s Hill radius of 53.5 million kilometers — interior to which Jupiter’s gravity dominates over the Sun’s tidal gravity. Eupheme has an orbital period of 588 days around Jupiter. It will reach its farthest distance of 27.7 million kilometers from Jupiter on January 23, 2026, just 52 days before its closest passage relative to 3I/ATLAS. This coincidence is not surprising given that there are 95 known satellites in orbit around Jupiter (as listed here). Eupheme was discovered in 2003 from data taken by the Mauna Kea Observatories in Hawaii. It is classified as an irregular moon and a member of the Ananke group, a family of 15 Jovian satellites which have similar orbits and are therefore thought to have a common origin. The Ananka group is thought to have originated from the breakup of a parent body that was captured by Jupiter’s gravity and fragmented into multiple pieces as a result of a collision with another object or from Jupiter’s tidal gravity. The largest relic of the parent body was named Ananke, and the smaller pieces constitute the additional 15 moons in the Ananke group. The Ananke moons orbit opposite to Jupiter’s spin on highly elliptical and inclined orbits relative to Jupiter’s equatorial plane. This is consistent with an origin associated with a captured parent body, rather than the primordial Jupiter system. Based on its brightness, Eupheme has a mean diameter of about 2 kilometers (for an assumed albedo of 0.04). In Greek mythology, Eupheme is the spirit of praise and good omen and the granddaughter of Zeus. Will 3I/ATLAS add new satellites to Jupiter’s family of 95 known moons? The proximity of the passage of 3I/ATLAS to the Hill radius allows it to release daughter objects into bound orbits around Jupiter. These small objects can become gravitationally bound to Jupiter as long as they receive a kick that cancels the relative motion between 3I/ATLAS and Jupiter. This relative speed will be relatively high at closest approach between the two objects, measuring about 66 kilometers per second. Discovering a fresh 96th moon around Jupiter after March 16, 2026 would constitute a clear technological signature for 3I/ATLAS. This is because a break-up of a natural astrophysical object which is much less massive than Jupiter cannot result in a velocity kick as high as 66 kilometers per second. The escape speed from the surface of Jupiter itself is 60 kilometers per second and gravitational break-up of much smaller bodies cannot generate fragments that are moving at larger speeds than the parent’s escape speed. Therefore, a kick of the required magnitude and direction to bring a fragment of 3I/ATLAS into a bound orbit around Jupiter is an impossible outcome from the break-up of a comet. In addition, the velocity kick must be highly fine-tuned because the escape speed at 3I/ATLAS’ perijove distance of 53.61 million kilometers from Jupiter is merely 2.2 kilometers per second — only a few percent of the relative speed, and so the direction and magnitude of the kick must be exquisitely designed in order for the encounter to result in a bound satellite. The outcome of the encounter between 3I/ATLAS and Jupiter will be monitored by the Juno spacecraft near Jupiter as well the biggest telescopes we have near Earth. Stay curious and get your popcorn ready by March 16. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

If 3I/ATLAS is a Comet, Why Would the CIA “Neither Deny, Nor Confirm” the Existence of Records on It?An image of 3I/ATLAS at 3:34 UTC on December 30, 2025 from nine 120-second exposures, taken with the Virtual Telescope Project facility in Manciano, Italy. A prominent anti-tail jet is clearly observed in the direction of the Sun, towards the lower left. (Image credit: Virtual Telescope)So far, 3I/ATLAS displayed a number of unexplained features relative to familiar comets — as I listed here. One could have hoped that these puzzles would trigger a healthy scientific debate about the nature of 3I/ATLAS. Instead, the case was officially closed by NASA officials without any discussion on the puzzling nature of these anomalies. The anomalous features include the existence of a prominent anti-tail jet directed at the Sun both before and after perihelion, the geometric alignment to within 8 degrees between the rotation axis of 3I/ATLAS at large distances and the sunward direction, the alignment to within 5 degrees of the orbital plane of 3I/ATLAS with the ecliptic plane, as well as the prominence of nickel relative to iron in the gas that 3I/ATLAS sheds — reminiscent of industrially-produced nickel alloys. On December 31, 2025, the Central Intelligence Agency (CIA) replied to a Freedom of Information Act (FOIA) inquiry by John Greenewald Jr., that it can “neither deny nor confirm the existence or nonexistence of records” related to 3I/ATLAS. The response was tweeted here. That this information is treated as sensitive enough to be classified by the CIA is surprising, given that NASA officials stated decisively at a press conference on November 19, 2025 (posted here), that 3I/ATLAS is definitely a comet of natural origin. If this conclusion was clear all along to everyone within government and academia — as NASA officials presented the case, then why would the CIA treat the possible existence of records dealing with a natural comet as sensitive enough to be classified? The simplest interpretation of the CIA response to the FOIA request is that some government officials wished to verify that 3I/ATLAS is not a black swan event, posing a potential threat to society even as comet experts regard such a possibility as highly unlikely. By multiplying a small probability for the existence of a threat with its high impact factor on society, the sober conclusion is that such events must be taken seriously and monitored. This lesson, akin to Pascal’s Wager, was learned the hard way by the residents of the City of Troy after they welcomed the Trojan Horse, as well as by intelligence agencies like the CIA after their miscalculations in gauging the risk from the events that unfolded on September 11, 2001 and October 7, 2023. Under such circumstances, NASA officials were encouraged to deliver the likely scientific interpretation, while at the same time — the serious consideration of a black swan event by the CIA was hidden from public view in order to prevent panic from taking hold for no good reason. This is a wise policy for mitigating societal unrest or instability of financial markets at a time when the reality of a black swan event is still regarded as highly unlikely. In order to maintain the public’s trust, the CIA would prefer not to raise a false alarm — like the shepherd who repeatedly shouted “Wolf!” — so when a real wolf came, no one believed him. The “neither deny nor confirm” is the best way to keep the investigation of black swan events hidden from view. If the above interpretation is correct, 3I/ATLAS represents the first case of an astronomical object for which the “neither deny nor confirm” response was adopted purposely by the intelligence agencies. During the summer months of 2025, I proposed the “Loeb Classification Scale” for the threat level of interstellar objects as alien tech. The scale was quantified in three peer-reviewed papers that I co-authored with Omer Eldadi, Gershon Tennenbaum and Oem Trivedi, which were first posted here, here and here. During the same time, I alerted policy makers to the possibility that 3I/ATLAS might be a black swan event, as mentioned here. Perhaps someone was listening to my request. Today, several reporters asked me for comments on the latest report (accessible here) on limits of technological radio transmission by 3I/ATLAS, based on data from the Green Bank Telescope. I clarified to the reporters that I encouraged the research team of the Breakthrough Listen Initiative to check for radio signals from 3I/ATLAS, because the arrival direction of 3I/ATLAS into the solar system aligned with the direction of the “Wow! Signal” from 1977 to within 9 degrees — with a chance probability of 0.6% as discussed here. The new data rules out a technological signal in the radio frequency band of 1–12 GHz towards Earth over a period of 5 hours between 04:15–09:15 UTC on December 18, 2025. It is unclear whether one should expect a technological object to transmit radio signals to its senders. Such signals would take several tens of thousands of years to cross the Milky-Way galaxy, whereas the time that 3I/ATLAS spends inside the solar system — all the way from and to the outer edge of the Oort Cloud, is only 16,000 years. Interstellar objects are unlikely to continuously transmit to their senders, because they do not have enough time to benefit from a two-way dialog. Given that their journey takes billions of years, the chance of a transmission on any particular 5-hour interval is miniscule. Moreover, such a signal may not be transmitted in the direction of Earth or at the frequency band that was monitored. To save energy, an efficient signaling would be beamed and compressed into a short burst with a small duty cycle. A proper observing program would have monitored 3I/ATLAS from many directions for a long period of time and not just over a 5-hour window. The data collection on 3I/ATLAS will not be over until it passes near the Hill radius of Jupiter. Hopefully, the curious community of government officials will be swayed by the dogmatic community of comet experts so as to check whether 3I/ATLAS deploys any small probes as new satellites of Jupiter. Unless we check, we might never know if this swan is white or black. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Stones from the Western Wall of the Second Temple in Jerusalem, knocked onto the street below by Roman battering rams on the 9th of Av, 70 C.E. This first century street is located at the base of the Temple Mount at the corner where the Western and Southern walls of the Temple met. (Image credit: Avi Loeb, January 2, 2025)Last week, I visited with my family the Old City of Jerusalem, which was constructed at ancient times by our civilization. This was a timely history lesson for me, given that my attention over the past six months was dedicated to the possibility that the interstellar object 3I/ATLAS might have been constructed by another civilization. What struck me in particular is one image of the Robinson Arch relic, which supported a flight of steps from a first century street of Jerusalem to the Temple Mount near the southern end of its western retaining wall. The arch was discovered in 1838 and named after its discoverer, the American researcher Edward Robinson. Under the Arch, I saw broken stones from the Western Wall that were thrown onto the street by the battering rams of Roman soldiers on the 9th of the month of Av (July-August), 70 C.E. Some of stones are blackened by the fire that consumed the Second Temple. A reconstructed miniature of the Old City of Jerusalem at the Israel Museum features the Second Temple in its full glory after its refurbishment was completed by the Roman Jewish King Herod the Great in 18 C.E., around the time when Jesus started preaching as a young Jew. A scale model reconstruction of the Temple Mount in the Holyland Model of Jerusalem, featuring the Second Temple in the Holyland Model of the Old City of Jerusalem. The model was designed by archaeologist Michael Avi-Yonah, based on archaeological evidence and ancient sources, and is housed at the Israel Museum, Jerusalem. (Image credit: Wikimedia)The refurbished Temple lasted only 52 years. Without getting into the political and strategic mistakes that led to the destruction, an external observer cannot escape feeling sad for the lost cultural treasures, in the form of books, art and scholarship. Their destruction transformed the history of Judaism and Christianity forever. But as we often see on social media, the destruction of cultural treasures of some is a reason for celebration by others. Roman forces led by Titus besieged the Jewish capital of Jerusalem. A year after the destruction they inflicted, the Roman Emperor Vespasian and his son Titus celebrated their victory with a Roman triumph event in Rome, parading temple spoils — including the Temple menorah — alongside hundreds of captives. Monuments such as the Arch of Titus were erected to commemorate the military victory. If any archaeological relics of the Temple lie underground, I am most curious to know whether the so-called Holy of Holies — where God’s presence was reported to appear in the Temple, included any technological transmitter to communicate with an extraterrestrial superhuman entity. However, any such relic — if it existed — must have likely been burned down and destroyed. Human history is full of alternating cycles of construction and destruction, with wounds that sometimes never heal. It is much easier to destroy than to build. Hence, destruction of cultural treasures signals a lack of intelligence. If humans were to cooperate instead of destroy, they would have reached greater heights. This is a particularly acute shortcoming given that all constructions on planet Earth will eventually be engulfed and destroyed by the envelope of the Sun in 7.6 billion years, like sand castles washed by the ocean. If we wish to be remembered in the long run, we better venture out of Earth rather than fight on its surface prior to our inevitable doomsday. The scars of tragic human history are marked by blackened stones from fires that consumed books in which the wisdom of past generations was recorded. Often, the historic disputes involved political control over real estate. But the reality that humans failed to recognize over and over again is that most real estate lies on 10^{20} Earth-analogs within the observable volume of the Universe. Surely, many inhabitants of these exoplanets engaged in cycles of destruction like us earthlings. But these are not the ones that will be remembered in the cosmic history books, summarizing the past 13.8 billion years. The written cosmic record will favor civilizations that engaged in cooperation aimed to explore what lies beyond their planet. Instead of burning down the cultural construction, they burned-up fuel to propel spacecraft. By recognizing that the cosmos is an infinite-sum game, they abondoned zero-sum games on the surface of their home planet. Will we ever reach that realization? It is difficult to be optimistic after reading the daily news. Extending Darwinian selection to interstellar space gives a new meaning to “survival of the fittest”. To find the fittest students in our class of intelligent civilizations, it is our scientific duty to invest billions of dollars in searching for them. The benefits will be huge if we succeed. Currently, the mainstream of the astronomy community focuses on the search for the chemical fingerprints of microbes in exoplanet atmospheres. But those who go on blind dates know very well that one is more likely to find a partner with qualities that exceed yours if one aims higher rather than lower. Imagining a better future for humanity could guide our search for a more advanced extraterrestrial civilization. Conversely, finding the products of such a civilizations would serve as inspiration for us to do better. Once we realize what it takes to become interstellar, we might do it. In that case, our new actions could serve as an inspiration for those extraterrestrial civilizations which have a lower rank than ours on the cosmic food chain. If they manage to communicate with our devices, they might construct a Temple on their exo-planet in their version of Jerusalem, to express a sense of awe towards more advanced technological accomplishments. The search for interstellar objects, like 3I/ATLAS, could carve the path for our transition from a past history marked by self-inflicted wounds to a future marked by cooperation and prosperity. Any communication chamber with extraterrestrials would constitute our future “Holly of Hollies” — where the presence of a superhuman alien technology will be celebrated. As 2026 starts, my New Year resolution is to focus my scientific attention to new interstellar objects that will be discovered by the NSF-DOE Rubin Observatory. Here’s hoping that one of them will carry an inspiring message in a bottle to all of us on Earth. Happy New Year! The Loeb family during a visit to Israel on the last week of 2025. (Image credit: Avi Loeb)ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Images of the jet structure of 3I/ATLAS from the Hubble Space Telescope, processed through the Larson-Sekanina rotation gradient filter, show a variable jet structure. The top panels zoom in on the inner jets within 24,000 kilometers from 3I/ATLAS on November 30, 2025 (top left), and December 27, 2025 (top right). Zooming out to the outer structure extending out to 100,000 kilometers, shown in the lower two panels for December 12 (bottom left) and December 27 (bottom right) is dominated by the anti-tail jet, directed at the Sun towards the lower left corner of the image. (Image credit: Toni Scarmato, based on data released by NASA/ESA/STScI here)Seventeen images of the interstellar object 3I/ATLAS, taken by the Hubble Space Telescope on November 30, December 12 and December 27, 2025, are accessible here. They reveal an intriguing configuration of evolving jets. On large scales out to 100,000 kilometers, the most prominent jet is an anti-tail directed towards the Sun, but on a scale that is 10 times smaller, there are three jets — one pointing roughly away from the Sun and two others pointing sideways in directions that are oriented +/-120 degrees relative to each other. The equal angular separations of 360 degrees divided by 3 among these three jet axes is puzzling. The orientation of the three axes is changing over time, presumably as a result of the rotation of the nucleus. The natural comet interpretation associates the jets with major pockets of ice on the surface of a rotating nucleus. The one that points at the Sun creates a prominent anti-tail jet that extends out to 100,000 kilometers. The activity of the other jets could be triggered by heat conduction through the body of the nucleus. The rotation period of 3I/ATLAS is about 16 hours (as reported here). Varying the extent of the minor jets by 5,000 kilometers over ~8 hours is possible with a jet speed of ~0.2 kilometers per second associated with the thermal speed of volatile molecules from the sublimation of ice by sunlight. However, having a coherent anti-tail jet on a scale that is an order of magnitude larger, requires stability over longer periods. This stability is possible if the rotation axis is nearly aligned with the direction of the Sun and the anti-tail jet precesses in a small cone around the rotation axis like the beam of a lighthouse. The anti-tail jet is ~10 times longer than it is wide. This suggests that its misalignment with the rotation axis is smaller than 6 degrees. The required geometric alignment of the rotation axis with the direction of the Sun has a small chance of 0.2% of occurring at random. Are the symmetric triple-jet inner structure or the unlikely alignment of the rotation axis with the direction of the Sun, technological signatures? Or can they be a natural outcome of gas dynamics? Time will tell. Before my morning jog at sunrise, I received the following uplifting message: “Professor Loeb, I would like to express my sincere thanks from Italy for your tenacity and determination to dismantle the obtuse dogmas of science that often make it impossible to accept the truth even when faced with it. The homeland of Galileo Galilei is grateful for your firm determination to stimulate a real and scientific debate, statistically more than plausible, from being shelved due to laziness and a lack of willingness to question one’s own dogmas. As an Italian, I would add that discoveries are something magical and unique, like love: you never know when it will arrive and which one will be the right one… but you can be sure that sooner or later it will arrive. And at that point, it is essential to be ready for the appointment. Even if this time isn’t the right one, in a starry sense, the special encounter will certainly happen. Statistics, too, is an empirical science… and the stars are hundreds of thousands of trillions! Ph. D. Davide Campailla Genoa — Italy” ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

If 3I/ATLAS is a Comet, then Its Anti-Tail Jet Should Not Include Streaming Gas Beyond ~5,000 kilometersFalse-color image of 3I/ATLAS (top panel), taken on December 27, 2025 by a 0.2-meter telescope in Belgium. The field of view is 14.4 by 23.3 arcminutes, corresponding to 1.1 by 1.8 million kilometers. Another image from the same telescope on December 19, 2025 which was processed through the Larson-Sekanina rotational gradient filter (bottom panel), shows a prominent anti-tail jet towards the Sun, as indicated by the yellow line in the inset. (Image credit: Alfons Diepvens)During the past two months after perihelion, the anti-tail jet from the interstellar object 3I/ATLAS was observed to extend out to a distance of several hundred million kilometers towards the Sun. In a previous calculation reported here and here, I showed that dust particles with a radius of order 10 micron could be dragged to a velocity of hundreds of meters per second by gas near their launch base and then reach a scale of several hundred million kilometers before being decelerated by solar radiation pressure. Will the outflowing gas accompany these dust particles out to the same distance or get pushed back more forcefully? Whereas the main pushback on dust stems from radiation pressure by sunlight, the main pushback on gas originates from the solar wind. Before being slowed-down, the mass density of the outflowing gas in the jet, D_j, declines inversely with the square of distance, d: D_j=Mdot/(2*pi*V*d²), where Mdot and V are the mass loss rate and velocity of the sunward jet. The total mass loss was estimated from data obtained by the Webb telescope before perihelion (as reported here) at a value of Mdot~150 kg/s and most likely grew by a factor of a few near perihelion. I therefore adopt an enhanced value of Mdot~500 kg/s for the post-perihelion anti-tail. In the context of 3I/ATLAS being a natural comet, volatiles from ices heated by sunlight yield a maximum outflow speed of the gas that is comparable to the thermal speed of the dominant constituent of CO2 molecules, V=0.2 km/s, as dictated by the surface temperature of ~200 degrees Kelvin at the current heliocentric distance of 3I/ATLAS of about twice the Earth-Sun separation (AU). This gives the gas mass density of the anti-tail as a function of distance from 3I/ATLAS: D_j~(1.6x10^{-17} g/cm³)/(d/5,000 km)² The solar wind carries about 3x10^{-14} solar masses per year per 4*pi steradian and flows at a speed of about v~500 km/s, providing a wind mass density at a heliocentric distance of ~2 AU: D_w~3x10^{-24} g/cm³. The jetted gas is expected to be stopped at a distance from 3I/ATLAS where its ram pressure (1/2)D_j*V² is balanced by the ram-pressure of the solar wind, (1/2)D_w*v². This occurs at a stopping distance: d_s~5,000 km. Interestingly, this is roughly the traverse radius of the glowing halo (coma) around the nucleus of 3I/ATLAS in the images of 3I/ATLAS (including the Hubble Space Telescope images listed here). As the solar wind sweeps up the gas, it carries it together with sub-micron dust particles away from the Sun along the tail of 3I/ATLAS. However, the large dust particles above 10-microns continue to stream along the anti-tail out to a scale that is ~10 times longer in the direction of the Sun. On that scale, the jet is expected to be gas-free if 3I/ATLAS is a natural comet where gas is launched at a speed dictated by the sublimation of CO2 ice on the surface of a natural rock and limited to ~200 meters per second. This result presents a clean test for the nature of 3I/ATLAS: if it is a natural comet, then the anti-tail jet should not include streaming gas beyond a distance of 5,000 kilometers from the nucleus. At distances much larger than 5,000 kilometers from 3I/ATLAS as a comet, the anti-tail should be composed primarily of a stream of 10-micron dust particles with no streaming gas. However, if the launch speed of the anti-tail jet is set by a technological thruster, then the extent of the streaming gas could reach much larger scales towards the Sun: 1. For chemical-propellant thrusters with an exhaust speed of V=5 km/s, the streaming gas could extend out to d=25,000 kilometers. 2. For ion thrusters with an ejection speed of V=90 km/s, the streaming gas could extend out to d=100,000 kilometers. The existence of streaming gas along the anti-tail can be tested through tagging a molecular tracer like CO2 or CO along the axis of the anti-tail jet and plotting the spatial profile of the tracer relative to scattered sunlight from dust inside the jet. Here’s hoping that such data will be collected by ground-based telescopes, like Keck, VLT or ALMA, or by space observatories like SPHEREx or the Webb telescope. Science is a learning experience. The best way to learn is by observing nature rather than forcing it to a popular narrative. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Images of 3I/ATLAS through 170 second exposures by the WFC3 UVIS (F350LP) camera of the Hubble Space Telescope, processed through the Larson-Sekanina rotation gradient filter, show a double jet structure. The left panel displays the data on December 12, 2025, and the right panel on December 27, 2025. The relative brightness of the two jets changes between these jets, either due to jet rotational wobble or source variability. The brightness is dominated by the anti-tail jet, directed at the Sun towards the lower left side. (Image credit: Toni Scarmato, based on data released by NASA/ESA/STScI here)New images of the interstellar object 3I/ATLAS, taken through 170 second exposures with the WFC3 UVIS (F350LP) camera of the Hubble Space Telescope at a central wavelength of 0.5851 micron on December 12 and 27, 2025, were released here. They reveal a double-jet structure. The more prominent jet is an anti-tail directed towards the Sun. False-color image of 3I/ATLAS, taken on December 12, 2025 through a 170 second exposure by the WFC3 UVIS (F350LP) camera of the Hubble Space Telescope (top panel), and processed with the Larson-Sekanina gradient filter (bottom panel). The more prominent jet towards the lower left corner is an anti-tail directed at the Sun. (Image credit: NASA/ESA/STScI; Color filter processing: Toni Scarmato)A sunward jet which is 10 times longer than it is wide was already captured in the Hubble image taken on July 21, 2025 (as reported here and analyzed here). Its 7-degree wobble around the rotation axis of 3I/ATLAS (as reported here) implied that it originated near the Sun-facing pole long before perihelion. The gravitational deflection of 3I/ATLAS by the Sun during perihelion on October 29, 2025, was only by 16 degrees, as I calculated here. If the rotation axis did not change orientation between July and December 2025, the original Sun-facing pole is now on the nightside of 3I/ATLAS — opposite to the direction of the Sun. It points in the same direction as the weaker jet in the new Hubble images from December 12 and 27, 2025, and is accompanied by a stronger sunward jet from the opposite side of 3I/ATLAS on its way out of the solar system. Raw image of 3I/ATLAS on December 27, 2025, taken with a 170 second exposure by the WFC3 UVIS (F350LP) instrument of the Hubble Space Telescope at a central wavelength of 0.5851 micron. (Image credit: NASA/ESA/STScI)Why are two jets displayed in the new images of 3I/ATLAS? There are two possible interpretations: 1. One possibility is that the two jets are launched from opposite sides of the nucleus. This would make the post-perihelion activity of 3I/ATLAS different than it was before perihelion. For a natural comet, heat conduction could transport the excess solar energy near perihelion from the dayside to the nightside and activate a weak jet on the nightside in addition to a stronger jet on the dayside. For a technological object, the sunward jet might be utilized for protection against the solar wind, coronal mass ejections or sunlight — given that the anti-tail is marginally opaque (as discussed here). In addition, the secondary jet could mitigate risk from obstacles lying ahead along its path. 2. The second interpretation is that both jets originate from the Sun-facing side but they have a different composition. As I described here, the anti-tail jet can extend out to several hundred million kilometers for dust particles with a radius of order 10-micron. However, the sunward outflow would extend only out to a few million kilometers in the sunward direction for sub-micron particles on which the solar radiative deceleration is 10–100 times stronger. A quick turnaround would also apply to gas particles which are swept away by the solar wind or to dust particles with a slow initial speed. All of these particles could therefore turn around quickly and constitute the second jet heading away from the Sun. The true origin of the jets can be inferred from measurements of the velocity profile of the two jets, based on future spectroscopic data from the Webb telescope. In the second interpretation, the weaker jet would also show a launch base on the sun-facing side of the nucleus and accelerate to an increasing recession speed with distance in the direction away from the Sun. In a technological context, both jets are expected to show a high-speed exceeding 1 kilometer per second at their launch points near the nucleus. Why do the jets look so different on December 12 and 27, 2025? Remarkably, the relative brightness and projected shape of the two jets changed significantly between December 12 and 27. This could be a signature of rotational wobble of the two jets, if they are misaligned with the rotation axis of 3I/ATLAS. But the difference could also indicate large variability of the jet sources. A simple way to identify the cause is to compare snapshots taken at different times over the 30-minute observing windows on both dates and identify systematic changes in them. The two Hubble images on December 12 and 27 favor the rotational wobble interpretation — as the anti-tail jet brightens when the opposite jet weakens, as expected from bobble of a double-jet structure around the rotation axis. As I argued here, the wobble or variability of the jets may explain the “heartbeat” changes observed with a period of 16 hours in the brightness of 3I/ATLAS in July 2025. As a result of mass loss, the rotation period of 3I/ATLAS may have changed by now (as discussed here in the context of the first interstellar object, 1I/`Oumuamua). My team will attempt to measure this possible evolution as we analyze the latest Hubble data on 3I/ATLAS. Science is exciting, as it offers us an opportunity to learn from new data. The only challenge is that we must stay humble in order to collect new data and learn something new, while self-declared experts provide us with old narratives based on past knowledge. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Image of 3I/ATLAS on Dec. 21.627, 2025 UTC (with a contour plot on the left). The jet to the right (west) is the anti-tail heading towards the Sun. The field is 6 by 12 arcminutes, and the exposure duration is 15 seconds on the NEOSSat 0.15-m Maksutov orbiting telescope. The coordinate grid is ecliptic 2000. (Image credit: D. D. Balam (DAO/NRC), C. E. Spratt (ret), D. W. E. Green (CBAT), P. Langill (RAO/U. of Calgary), Omar Elmi (CSA), Jack Williams (CSA) & Canadian Space Agency)In my latest two essays, accessible here and here, I showed that the characteristic radius of dust particles in the anti-tail jet launched from the interstellar object 3I/ATLAS is of order ~10 microns. This conclusion was based on the observed length of the jet and the requirement that the dust particles reach the jet speed through drag on the outflowing gas. Given these requirements, I derived here the mass density D of gas in the outflow at a distance d from the nucleus center, D~(3.2*10^{-8} g/cm³)*(d/1km)^{-2}, Later, I derived here that ~0.7% of the total mass loss after perihelion is carried by ~10-micron dust particles. The mass of each 10-micron dust particle is m~10^{-8} g, implying that the particle number per unit volume near the base of the jet is: n~(0.7%)*D]/m= 2.2 cm^{-3}*(d/1km)^{-2}. The cross-sectional area of each 10-micron particle for scattering sunlight is: S=pi*(10^{-3}cm)²= 3.14*10^{-6} cm². Therefore, the scattering probability of sunlight from outside down to a distance d from the nucleus center is given by: P = (n*S*d) ~ 0.7*(d/1km)^{-1}. The minimum value of the radial distance d is the radius of the nucleus, R_n: minimum{d}=R_n. If the scattering probability P exceeds a value of unity, then the nucleus surface of a natural comet would not be exposed to sunlight and the release of gas or dust would stop. This implies that the radius of the nucleus for a natural comet must be larger than the value of d which yields P~1, namely: R_n> 0.7 km, corresponding to a minimum nucleus diameter for 3I/ATLAS of ~1.4 kilometers. This lower limit applies only if the jet results from the illumination of the nucleus of a natural comet by sunlight. On the other hand, if the release of dust is intended to protect a technological object from sunlight, then a value of P>1 around the nucleus will be favored by design as a protective blanket. In this case, the nucleus of 3I/ATLAS might have a radius R_n<0.7 km which cannot be resolved in scattered sunlight by an external observer. Either way, it is a remarkable coincidence that P is of order unity for the inferred size and mass loss rate of 3I/ATLAS. This coincidence could be a natural consequence of a self-regulating feedback loop that keeps the value of P close to ~1 because a larger value suppresses the release of dust whereas a smaller value enhances the release of dust, bringing the density of dust at the base of the jet to yield P~1. But it could also be a protective measure of an artificial origin. In summary, the blanket of dust surrounding 3I/ATLAS is on the borderline between it being opaque and transparent to sunlight. This means that imaging by an external camera with a sub-kilometer spatial resolution would have likely shown a fuzzy cloud of dust rather than a nucleus with a sharp boundary. 3I/ATLAS is hiding behind a veil of dust. *** Before my morning jog at sunrise, I received the following uplifting message: “Dear Professor Loeb, I wanted to thank you for your work — not only for its scientific substance, but for the example it sets. You have shown — publicly and consistently — that science is not about defending answers, but about protecting questions. That stance has inspired many people, especially young ones, to see science not as a closed guild of certainties, but as an open-minded, intellectually demanding adventure. A few excerpts came to mind that I think resonate strongly with your approach: Václav Havel once wrote: “Keep the company of those who seek the truth — run from those who have found it.” That sentence could double as a survival guide for modern science. I have replaced the word “psychoanalyst” with “scientist” in this letter of Anna Freud from the 1960s and the result holds true: “If you want to be a real [scientist] you have to have a great love of the truth, scientific truth as well as personal truth, and you have to place this appreciation of truth higher than any discomfort at meeting unpleasant facts.” And finally, a line from Spielberg’s 2002 mini-series Taken that has stayed with me: “Life is about asking questions, not about knowing the answers. It’s what lies over the next hill that keeps us going.” Your work embodies that spirit. For many aspiring scientists, it quietly gives permission to be curious, intellectually honest, and a little bit brave. Wishing you a New Year with more good questions than comfortable answers. Alex Zivoder Luxembourg” ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Images of the interstellar object 3I/ATLAS from the Two-Meter Twin Telescope (TTT) and the Transient Survey Telescope (TST) located at Tenerife, Spain (right panels), and the corresponding Laplacian-filtered images (left panels). The observation date, start and end times (UTC), number of sidereal-tracking exposures, and total integration time are indicated above each panel. The projected velocity vector of 3I/ATLAS (red arrow) and the anti-solar direction (yellow arrow) are shown, along with the image scale and orientation. Red cross marks the brightness peak. The direction of the anti-tail and tail are marked by thin red and yellow lines, respectively. Brightness contours of the original image are overplotted on the left panels, using ten logarithmically spaced levels between the 80th and 95th percentiles of the pixel-intensity distribution. The pixel size is 0.60 arcseconds and the field of view is 2.4 by 1.8 degrees. (Image credit: M. Serra-Ricart et al. 2025)In my latest essay — accessible here, I showed that the characteristic radius of dust particles in the anti-tail from 3I/ATLAS must be much bigger than 1 micron in order for them to reach the observed length of this jet and much smaller than 100 microns in order for them to reach the required jet speed through drag on the outflowing gas. My calculation implies that the anti-tail contains dust particles with a characteristic radius of order 10 microns. The mass loss rate carried by these dust particles can be estimated from the brightness of glow surrounding 3I/ATLAS. The total luminosity of the glow around 3I/ATLAS during the month after perihelion is equivalent to the reflection of sunlight from a spherical mirror of 10-kilometers radius, which is a billion (10⁹) times larger than the 10-micron radius of a dust particle. Since area scales as radius squared, there must be (10⁹)²=10^{18} dust particles to yield the total luminosity of scattered sunlight in the glow around 3I/ATLAS. Since the mass of a single 10-micron dust particle is ~10^{-8} grams, the total mass in scattering particles is 10 million kilograms. The duration over which this mass must be supplied is of order the solar deceleration time of the dust particles, after which the dust is dispersed. For the jet length L=400,000km, and the solar deceleration value of A~0.01cm/s² associated with particle radius of R~10micron, we get a required supply time, t_supply ~ (2L/A)^{1/2} ~ 1 month = 3 million seconds. This implies a mass loss rate in 10-micron dust particles of 10 million kilograms in 3 million seconds or ~3.3 kg/s, which is a fraction of 0.7% of the total mass loss rate of gas Mdot~500 kg/s. The dust to-gas ratio in the interstellar medium of the Milky-Way galaxy is similar, of order ~1%, but most of it is in particles with a radius below 1 micron. However, in molecular clouds, larger dust particles with R~10micron are made. This raises the question: Did 3I/ATLAS originate from a molecular cloud, where it collected 10-micron dust particles on its surface? The additional anomalies of 3I/ATLAS (listed here) raise other questions about its nature, to which we do not have answers yet. Being honest about what we do not know, would motivate us to seek answers. Those who are not curious about the unknown and fill their mind with pride about what they know, end up being dull. Below is a delightful correspondence with a young girl who was inspired to become a scientist after viewing one of my interviews. She gives me hope that the next generation of scientists will be better than those who came before them. — — — — — — — — — — — — — — — — — — “Dear Dr Loeb, We watched your interview video in science class today. I showed my teacher and my friends that you responded to my email. I don’t know what a white letter means? I saw it went to the United Nations and […] they are going to monitor 3I/ATLAS. That’s good but I hope it’s not bad aliens. Only good aliens. Like the little gray aliens. I’m not afraid of them because they are as short like me. Thank you, Dr Loeb. I read your Medium.com articles every day. Have a wonderful week. Arianna — — — — — — — — — — — — — — — — — — Dear Arianna, I had mentioned you on the Joe Rogan podcast, so you can share it with your class. I hope they will enjoy the podcast which should be available on Spotify and YouTube. Avi — — — — — — — — — — — — — — — — — — You mentioned me? […] I’ll have to ask my dad if I can watch Joe Rogan. Why isn’t NASA releasing the clear photos of 3I/ATLAS? Something is very fishy, Dr Loeb. My dad says NASA lies to the people like parents lie to their children when they don’t want to tell them the real truth. But kids already know anyway. I’m sure my dad will let me see you on Joe Rogan. I’m so excited to show people at school. Have a wonderful week. Thank you for all you do for bringing the truth to light. Arianna — — — — — — — — — — — — — — — — — — Hey Dr Loeb, My dad, brother and I watched your Joe Rogan interview and you were great. I can’t believe Joe Rogan didn’t know what Oumuamua was. Our first interstellar object. Or the first one we’ve noticed. I think there have been many more before. I told my science teacher you mentioned me and he told Ms. Graves who does our morning announcements and she told the whole school. It was funny. My dad loves they put you on a race car. Him and my brother love race cars but I just like soccer and science and some math. I have soccer practice now. Have a great weekend. Arianna — — — — — — — — — — — — — — — — — — Dear Arianna, I also love soccer and science. Glad to hear that we think alike! Avi — — — — — — — — — — — — — — — — — — Really? You play soccer also? That’s so cool. I’m really good. I play right wing and sometimes goalie. But I don’t like being the goalie when it’s cold outside because stopping the ball hurts my fingers. We are going to see 3I/ATLAS again tomorrow, right? And we will know in a few days if it’s aliens or not. I hope it’s not scary aliens. Only the gray ones because they are shorter than me. I wonder if they play games like soccer. I asked dad why we don’t have small AI telescopes in orbit around the Sun but opposite the earth? That way we will never be blind of another visitor again? They can also keep a lookout for asteroids. Same with the moon? If we put telescopes on both sides of the moon from our viewpoint then we can send probes to the far side of the moon without losing contact. I’m making a list of things we need. They can probably be very small so they won’t be expensive. I can probably go to Home Depot and get everything to make it. I just don’t know how to make it stay in one place without flying away. Maybe we find a balance from the moon’s gravity and the earth and then it won’t move. Because they are so small we can get them in space with tiny rockets. I think small is important. I have to go to bed. I’m glad you like soccer. Maybe we can teach the aliens to play. Arianna — — — — — — — — — — — — — — — — — — Thank you, Arianna. Here is an essay with my photo playing soccer: https://avi-loeb.medium.com/does-3i-atlas-generate-its-own-light-e9775594afc5 Happy Thanksgiving! Avi — — — — — — — — — — — — — — — — — — Hey Dr Loeb, I hope you had a wonderful Thanksgiving. I love macaroni and cheese so I had a lot of that. I know you are very busy because I read your Medium.com post and watch your TV and podcast interviews. Why am I seeing legitimate amateur astronomer’s uploading photos that are way more detailed than the silly NASA images. They just make me mad and not even want to be interested because they tell lies. I get in a lot of trouble when I lie but they don’t. My soccer team won first place and we got trophies. That was really cool. Happy holidays and I hope you have a blessed new year with great achievements. Arianna — — — — — — — — — — — — — — — — — — Wonderful to hear from you, Arianna. I am delighted to hear that your soccer team won first place. You won first place in my heart long ago and I hope you will become a scientist and solve many of the mysteries that my generation and NASA failed to solve. Avi — — — — — — — — — — — — — — — — — — Hi Dr Loeb! It’s Arianna. I’ve been reading all of your published papers on Medium. I love when I get home from school and I see new papers. I got all A’s in school except one B in French. That’s a difficult language for me. Plus, my teacher is from Paris and she is difficult to understand. I got a perfect 100 in science. […] My dad flew F-22s […] I hope you and your family have a wonderful Holiday season. And happy Hanukkah. I have a friend who celebrates Hanukkah and she gets presents every day for a long time. That’s cool! Okay, I got a RC F-22 aircraft and we are going to my school soccer field to fly it. I told my dad I wanted to be a girl F-22 pilot but he said he thinks all planes will be autonomous when I get big so then I want to be a scientist. He said AI might have those jobs also. But I’m smarter than AI. They only know what we teach them and I won’t tell them everything. Bye Arianna — — — — — — — — — — — — — — — — — — Hi Arriana, Great to hear from you. You should aim to become a scientist because — as your father says — planes will be piloted by AI, but science will not. Today, I met with someone who used AI to propose a new theory of gravity. He worked on it for years, but I showed him that his theory is ruled out in a few minutes. I told him that natural intelligence is better than artificial intelligence. For now, keep excelling in soccer and studies. You sound just like me when I was your age! Avi — — — — — — — — — — — — — — — — — — ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Images of the tightly-collimated anti-tail jet from 3I/ATLAS in the sunward direction (lower left), as processed through a Larson-Sekanina gradient filter on December 15, 2025 (top) by Toni Scarmato, and on December 13, 2025 (bottom) by Teerasak Thaluang.Recent images of the interstellar object 3I/ATLAS show a tightly collimated anti-tail jet that extends out to at least 100,000 kilometers in length towards the Sun. It is commonly assumed that the glow in this jet results from the scattering of sunlight by dust particles. Here we derive constraints on the characteristic size of these particles, assuming that they originate from a natural comet. If these particles start with an initial velocity V, then they can reach a distance L before being stopped by the solar radiative deceleration A: L=V²/(2A). The solar radiation force on spherical particles with a radius of R larger than the wavelength of sunlight is of order the momentum flux carried by sunlight at a heliocentric distance r, namely: ~L/(c*4*pi*r²) where L is the solar luminosity and c is the speed of light, times the cross-sectional area of the particle, namely: (pi*R²). At a heliocentric distance of r~2au, where the recent images were taken, the solar deceleration for a particle with solid density of 1g/cm³ is: A~ (0.1 cm/s²)*(R/1micron)^{-1}. Therefore, to reach L~100,000km, the initial velocity of these dust particles must be V~(450m/s)*(R/1micron)^{-1/2}. For sub-micron dust particles, this velocity exceeds the thermal speed of gas particles at that heliocentric distance and is therefore untenable. Such a velocity cannot be reached if 3I/ATLAS is a natural comet, even if the dust is perfectly dragged by outflowing gas from the sublimation of volatiles on the surface of an icy rock by sunlight. The solar deceleration scales inversely with particle radius and should be larger for smaller particles with a radius comparable to the characteristic wavelength of sunlight, ~0.5micron. In conclusion, the observed length of the anti-tail generated by 3I/ATLAS can only be sustained by particles with a radius much larger than common dust particles which have the largest surface area per unit mass for scattering sunlight and usually dominate the glow around solar-system comets. 3I/ATLAS is therefore anomalous in the size of the particles that dominate the glow of its sunward jet. The anti-tail glow of 3I/ATLAS is dominated by particles that are bigger than the typical dust particles that scatter sunlight most efficiently. This is required to explain why the sunward jet of 3I/ATLAS is much longer than observed in familiar comets. From its discovery, the observed anti-tail jet was inferred to be 10 times longer than it was wide — after correcting for its projection angle of 10 degrees in the Hubble image from July 21, 2025 (as reported here and analyzed here). The tight collimation of the anti-tail jet of 3I/ATLAS might be the result of the release of large particles from a very small fraction of the surface of the nucleus. In addition, there is also an upper limit on how big these anti-tail particles can be. Much larger particles have a smaller surface area per unit mass and cannot be easily dragged by gas to the required high-speed V. The mass loss from the Sun-facing side of 3I/ATLAS was estimated from data obtained by the Webb telescope (as reported here) at a value of Mdot~150kg/s and could have grown by a factor of a few near perihelion. For our calculation, we will adopt an enhanced value of Mdot~500 kg/s for the post-perihelion anti-tail, observed over the past couple of months. Given this mass loss rate, the outflowing gas density D declines inversely with the square of the distance d from the nucleus of 3I/ATLAS, according to the relation: D=Mdot/(O*V*d²) where O is the conical solid angle of the outflowing sunward jet. The recent images of 3I/ATLAAS imply that the anti-tail jet is collimated to within a cone with an opening angular radius of about 8 degrees — corresponding to O=0.06. Using this value along with the derived expression for V, gives a jet mass density as a function of distance d: D~(2x10^{-8}g/cm³)*(R/1micron)^{1/2}*(d/1km)^{-2} The time required for drag to bring a solid-density particle of radius R to the velocity of the outflowing gas V is: ~8R/[V*(D/1g/cm³)] ~ (1s)*(R/1micron)*(d/1km)^{2} This drag time scales as (R*O/Mdot)*d² and does not depend on the initial outflow speed of the gas V (which eventually is assumed to be matched by the particles through drag). This drag time must be shorter than the jet dilution time over which the outflowing gas gets rarefied with distance d from the nucleus: ~(d/V)=(2s)*(d/1km)*(R/0.1micron)^{1/2}. This inequality is only possible for particles that are sufficiently small, with: (R/100micron) < (d/200m)^{-2}. For the typical particle radius to be larger than 100 microns, the nucleus radius must be smaller than 200 meters. This is not allowed by the lower limit on the nucleus radius, as derived here from the Hubble image data. Adopting a more modest value of Mdot near perihelion would reduce the limit on the maximum particle size. In conclusion, the radius of the particles in the outflow from 3I/ATLAS must be bigger than 1 micron in order for them to reach the observed length of the anti-tail jet and smaller than 100 microns in order for them to reach the required jet speed through drag on the outflowing gas. These requirements apply to a natural comet where the anti-tail is sourced by sublimated ice, but not to an exotic source — like the exhaust of a rocket that could endow the particles and gas with an arbitrary ejection speed. Further constraints on the typical particle size could be derived through a direct measurement of the velocity V of the sunward jet by a spectroscopic measurement of its Doppler shift relative to the nucleus of 3I/ATLAS. *** As we attempt to quantitatively characterize the interstellar object 3I/ATLAS, we must keep in mind what Erwin Schrödinger, a prominent founder of quantum mechanics, said about scientific insights: “The task is not so much to see what no one has yet seen; but to think what nobody has yet thought, about that which everybody sees”. *** This morning, before my routine 3-mile jog at sunrise, I received the following message: “Dr. Loeb, Thank you so much for all of your excellent 3I/ATLAS coverage! It has been an absolute thrill to follow along with each new piece of mind bendingly perplexing data we’ve been gathering on this interstellar object! I’ve always been interested in what’s out there beyond the stars, but never have I been so captivated by any space object as I am by 3I/ATLAS. I love that it’s forcing people to ask difficult questions and rethink what’s possible in regards to how physics work in solar systems beyond our own. Thank you for having the courage to share your hypothesis and thoughts on what 3I/ATLAS might be, and all of the different possibilities. Your ability to vividly imagine reminds me of this beautiful Einstein quote: “Imagination is more important than knowledge. For knowledge is limited to all we now know and understand, while imagination embraces the entire world, and all there ever will be to know and understand.” Take care and have a great New Year! Respectfully, Drew” ABOUT THE AUTHOR Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.View the full article

Data from radio observations of 3I/ATLAS by the Allen Telescope Array on July 2, 2025, showing a signal in both the on-beam and the off-beam panels, indicating a local interferer in the allocation allotted to fixed-satellite service (Earth-to-space). (Image credit: S. Sheikh et al. 2025)A new paper, posted here, reports data from 7.25 hours during July 2, 2025 of radio observations of the interstellar object 3I/ATLAS with the Allen Telescope Array. Within the frequency range of 1–9 GHz, there were nearly 74 million narrowband hits. After mitigating Radio Frequency Interference in the dataset, only about 2 million hits were left. These hits were further filtered by sky localization. The vast majority of them did not coincide with 3I/ATLAS on the sky. The remaining 211 hits were visually inspected in the time-frequency domain and the observers did not find any signals worthy of additional follow-up. Accounting for the radial velocity (Doppler) drift of 3I/ATLAS, the upper limit deduced on the isotropic radiated power of 3I/ATLAS is in the range 10 to 110 Watts within the observed range of radio frequencies. The team plans to re-observe 3I/ATLAS in December 2025. *** Non-gravitational accelerations (top panel) and their corresponding mass loss rates (middle and bottom panels) for 3I/ATLAS. The inferred diameter of the nucleus is of order 1 kilometer. (Credit: J.C. Forbes and H. Butler 2025)In another new preprint posted today here, the latest data on the non-gravitational acceleration of 3I/ATLAS was combined with data on its mass loss rate to conclude that the diameter of its nucleus is of order 1 kilometer. This size estimate is consistent with the value predicted in my first paper on 3I/ATLAS, published in early July here. The estimate follows the momentum conservation equation that I posted three months ago here, where the non-gravitational acceleration results from the recoil of 3I/ATLAS -associated with a mass loss in a preferred direction. However, there are several uncertainties that might alter this estimate considerably: 1. The non-gravitational acceleration was downsized multiple times since November 2, 2025 by NASA’s JPL-Horizons listing here. Its normalization depends on the sky-localization uncertainties assigned to telescope images of 3I/ATLAS, as well as on the model adopted for the dependance of the acceleration on distance from the Sun. 2. The momentum imparted to the nucleus of 3I/ATLAS could be dominated by the ejection of fragments of icy material (as discussed in the paper that I co-authored with Eric Keto here), rather than gas particles at their thermal speed. 3. The directionality and the ejection speed of the material from the surface of the nucleus could be different from their assumed values. Currently, there is no spectroscopic measurement of the velocity of the observed jets in images of 3I/ATLAS. Hopefully, future observations by the Webb telescope will measure the jet velocities. 4. The dominant anti-tail jet appeared to be in the direction of the Sun both before perihelion (as evident form the Hubble Space Telescope image on July 21, 2025 here) and after perihelion (as evident from the Hubble image on November 30, 2025 here). The direction of the trajectory of 3I/ATLAS was deflected by the Sun’s gravity only by 16 degrees at perihelion (based on my calculation here), and so the momentum given to the nucleus by the anti-tail jets before and after perihelion nearly cancel out. The current analysis does not take into consideration the evolution in the direction of the jets during the past 6 months. Science is fun as a learning experience. At the end of my new podcast interview with Dr. Brian Keating (accessible here), I pointed out that some people choose to dedicate their body to science after their death. On the other hand, I choose to dedicate my body to science while I am alive. The fascination with science was echoed in a letter that I received before my morning jog and the impending snow storm at sunrise: “Dear Professor Loeb, I am from Mauritius, a tiny island in the Indian Ocean. I have been following you since the Oumuamua appearance. I am deeply touched by your recent remarks, quoted as follows: “The foundation of science is the humility to learn, not the arrogance of expertise” If the scientific community were inspired by this saying, we would already have a dedicated probe near 3I/ATLAS today. Just like I am, from where I live, an infinitely small point on the surface of the earth, the latter is also in the same situation as compared to the Universe. Consequently, humility to learn should be our natural motto in the scientific community rather than arrogance of expertise, as you rightly wrote. Yours faithfully, Ranjeet Kallychurn” ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

(Image Credit: Naeblys/Istock/Getty Images)The Loeb scale ranks interstellar objects on a scale between 0 for natural icy rocks (comets or asteroids) to 10 for alien technology that is a potential threat to humanity. The Loeb classification was quantified in two peer-reviewed publications, available here and here. This quantitative classification was expanded a week ago in a new paper here to a formalism that evolves the ranking of an interstellar object as new data about it comes in. Shortly after 3I/ATLAS was discovered in July 2025, I ranked is as 4 on the Loeb Scale. When asked to update the rank recently, I declined to do so until new data from the period bracketing its closest approach to Earth is publicly released and analyzed. The new data release may not conclude before 3I/ATLAS arrives closest to Jupiter on March 16, 2026. In a recent interview on NewsNation (available here), I was asked by Elizabeth Vargas to clarify my standpoint about the nature of 3I/ATLAS. In response, I repeated what I said before — that 3I/ATLAS is most likely a natural object. This response was highlighted as news but it is not so. I expressed the same standpoint as early as July 2025. This is evident from the Conclusions section of my peer-reviewed publication here, as well as from the content of many of my essays — such as the essay posted here on July 27, 2025. In answer to a reporter’s question, posted here on October 29, 2025: “Do we know about whether it really is a natural comet or something else?”, I responded: “3I/ATLAS is most likely a comet of natural origin, but there are 8 anomalies that endow it with a rank of 4 on the Loeb scale.” Back on October 29, I flagged 8 anomalies of 3I/ATLAS, but by now the number grew to 15 — as listed here. My standpoint all along was that we must consider the technological interpretation seriously because of the possibility of a black swan event with low probability and huge implications to humanity. Following the dismissal of black swan events on September 11, 2001 and October 7, 2023, intelligence agencies worldwide revised their practices and they now attempt to collect as much data as possible on low-probability events with major implications. This echoes the philosophical rationale in Pascal’s Wager. Scientists are not used to a `black swan mindset’, because their research rarely has immediate and major implications to society. Having an unknown visitor from the cosmic street to our backyard requires that we stay alert to the risk from it entering our home, especially when its tail is coming from its forehead rather than its back — as is the case in common street cats. Nothing has fundamentally changed about my standpoint as of yet. The NewsNation interview reflected my previous arguments. The real update will come as a result of the analysis of new data in the coming months. The most revealing data will likely involve the spectrum of the anti-tail jet, which stretches across a million kilometers towards the Sun in the latest images. Measuring the speed and composition of the anti-tail would distinguish between an origin from the sublimation of natural pockets of ice on the surface of a rock versus a technological thruster. In the first case, we should find CO2, CO and H2O gas moving at a maximum speed of hundreds of meters per second, whereas in the second case the jet composition might appear to be anomalous and the exhaust speed could be orders of magnitude larger. And of course, any release of smaller objects near Jupiter, and the detection of artificial lights or unexpected maneuvers, might also constitute a technological signature. But in the absence of a clear technological signature, I will revise my Loeb Scale rank downward. Science is done in a more reliable fashion than the quality of news reports. Stay tuned. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Analysis of the image of 3I/ATLAS at its closest approach to Earth on December 19, 2025. The top row shows the brightness maps in different wavelength bands (R-centered on 0.659, G-centered on 0.530 and Blu-centered on 0.445 micrometers). The bottom row shows the brightness map from the Larson-Sekanina gradient filter, featuring a prominent anti-tail jet in the sunward direction, towards the lower left. The appearance resembles a rocket receding way from the Sun. (Image credit: Toni Scarmato)The Voyager Golden Records, containing a time capsule of sounds, images, music and messages from Earth, were attached to NASA’s Voyager 1 and 2 spacecraft which are currently traveling out of the solar system. These records serve as humanity’s message for any intelligent extraterrestrial life that might find them, essentially a “message in a bottle” sent out to interstellar space. If we are impatient in establishing physical contact with extraterrestrials, we can attempt to do better in reaching our cosmic neighbors with technological artifacts. Traditional thinking would argue that we must construct a faster spacecraft to overtake Voyager and be recognized earlier. Indeed, interstellar artifact collectors might discover our fastest technologies first if their shorter travel times compensates for their later launch dates. Voyager 1 was launched on September 5, 1977; coincidentally, just a few weeks after the extraterrestrial Wow! Signal was detected. Voyager 1 is traveling out of the solar system at a speed of 17 kilometers per second. It is currently at a distance of about 170 times the Earth-Sun separation (AU). Interstellar space starts outward of the boundary of the Oort Cloud at about 100,000 AU, inside of which icy rocks are still bound by gravity to the Sun and show up near Earth as long-period comets. Voyager 1 will reach that boundary in about 28,000 years. In contrast, the interstellar object 3I/ATLAS has an outward speed of 60. It will return to interstellar space in about 8,000 years. Riding 3I/ATLAS offers the benefit of reaching interstellar space by the year ~10,000 CE instead of the year ~30,000 CE. The discovery of interstellar objects over the past decade offers new opportunities for humanity to send time capsules to interstellar space. One approach would be to design interceptor missions that would deposit analogs of the Voyager’s Golden Records on the surface of a large interstellar object like 3I/ATLAS, with the hope that these records will be recognized by interstellar archaeologists. Another approach is to use a high-power laser beam to carve a message on the dry surface of an interstellar asteroid. Will this effort be worthwhile if extraterrestrials will not notice our technological marks on interstellar objects? This question echoes the famous philosophical though experiment: “If a tree falls in a forest and no one is around to hear it, does it make a sound?” With the mainstream mindset of terrestrial astronomers, we would certainly miss any such markers. But there is also a practical limitation. Our largest telescopes both on Earth and in space do not have sufficient angular resolution to resolve a billboard sign with letters as big as Manhattan Island at a distance of order the Earth-Sun separation. However, if any extraterrestrial billboard with letters that big shows up at a distance smaller than 0.1 AU, it will open up a new discipline on university campuses labeled as “Interstellar archaeology”. Recognizing technological imprints on asteroids or comets from interstellar space would provide the cosmic perspective that we desperately need in our daily routines. Terrestrial museums featuring replicas of these imprints will likely attract larger audiences than Science Fiction movies. Of course, there could also be functional instead of artistic imprints of technology on the surfaces of interstellar asteroids. These would mark attempts of extraterrestrials to mine them for precious minerals or fuel (as discussed here). Future interceptor missions, like ESA’s Comet Interceptor (as described here and here), could get close to interstellar objects and provide close-up photographs of them (as discussed here). The existence of artificial lights or infrared excess from the heat generated by a technological power source inside an interstellar asteroid or a comet, could also be identified in Webb space telescope spectroscopy from a large distance. Here’s hoping that our travel agencies will realize that interstellar objects offer a fast ride out of the solar system. If offered the opportunity, I would have loved to hitchhike 3I/ATLAS and let it carry my remains into interstellar space. How long will it take 3I/ATLAS or Voyager to reach the opposite side of the Milky-Way disk of stars? Of order one billion years. Since most stars formed billions of years before the Sun, any civilization near them would have had plenty of time to reach our backyard. Their technological Golden Record or the remains of their most ambitious explorers might be buried in interstellar spacecraft even if those were propelled by a copy of our rocket technologies from the 1970s. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

An image of 3I/ATLAS at its closest approach to Earth on December 19, 2025, featuring a prominent anti-tail jet in the sunward direction, towards the lower left. (Image credit: Dr. Sebastian Voltimer)Humans are interesting cosmic creatures. More than four centuries ago, we were convinced that the Universe centers on us. Recently, we realized that there are about ten billion houses like ours on the cosmic street of the Milky-Way and most of them formed billions of years before the Earth-Sun system. However, our popular view is that visitors from these houses might show up in our cosmic neighborhood because of their interest in our home. Well, guess what: if you are late to a party and you are not at the center of the room, the party is not about you. Not only are we not at the center of the Universe, we are also not at the center of attention for interstellar visitors. This blunt message-in-a-bottle was delivered to earthlings on December 19, 2025, by the interstellar object 3I/ATLAS, as it reached its closest distance from Earth, 268.91 million kilometers. 3I/ATLAS did not maneuver or display any unusual activity on that occasion. Its trajectory is aligned to within 5 degrees with the ecliptic plane but it avoided Earth by passing on the other side of the Sun relative to us on October 29, 2025. Some find this message insulting. But the truth of the matter is that with an interstellar speed of 60 kilometers per second, the journey of 3I/ATLAS through the Milky-Way disk of stars must have taken billions of years. When 3I/ATLAS started its journey, there were no humans on Earth. And besides, among the solar system planets — Jupiter is the center of attention given that its mass is 318 times larger than Earth’s. Humans arrived late to the local cosmic party, only to witness the last 0.0001 of the Milky-Way history. Given that, we should not be surprised that interstellar visitors — who attended the party for much longer, did not plan to dance with us. So far, December 19 images of 3I/ATLAS were only released by amateur astronomers. They feature a prominent anti-tail jet pointed at the Sun, ten times longer than it is wide, with a length of a million kilometers. We have never witnessed such a long, tightly collimated anti-tail. To fully understand the nature of 3I/ATLAS, we must explain this anomaly as well as the others listed here. In the coming months, imaging and spectroscopic data will help us figure out the mysterious properties of 3I/ATLAS by the time it gets closest to Jupiter on March 16, 2026. The forecasted perijove distance of 53.6 million kilometers is close to Jupiter’s Hill radius, 53.5 million kilometers (as discussed here), where Jupiter’s gravity dominates over the Sun’s tide. Given that Jupiter is the largest planet in the solar system, it would be interesting to monitor 3I/ATLAS with the Juno spacecraft for any unusual activity as it passes by Jupiter’s Lagrange points. I delivered the above sentiments in seven television interviews during the perigee day of 3I/ATLAS. After the last interview, I received the following email from the brilliant Gadi Schwartz at NBC News: “Speaking to you is always the highlight of our day! And the amount of little future astronomers you have inspired is incalculable!!! Here’s the latest AI imposter I spotted! (CHATgpt tells me deepfakes should be taken as are the highest form of flattery!)” Indeed, fake content manufactured by artificial intelligence will be the biggest nemesis of science for years to come. My hope lies with natural intelligence. To gain respect near the top of the food chain in the Milky Way galaxy, we must endeavor to interstellar space. During his first day in office, the new NASA administrator, Jared Isaacman, commented here on the importance of extending our space exploration plans beyond the Moon and Mars. Also, during his annual televised news conference on December 19, 2025, accessible here, Russian president Vladimir Putin was asked by a reporter about3I/ATLAS. Here is the transcript of the exchange: “Journalist: I have a question about the unusual object 3I Atlas which is currently approaching us. If the predictions are to be believed today, December 19th, either a spacecraft with an engine or just a comet will approach Earth. My question is this, what do intelligence services report to you? Are there really signs of artificial origin? As funny as it may sound, there are indeed many theories and speculations. We, at Tyumen — the oil capital of Russia, are ready to welcome any guests but if they are from space we would like to prepare. Secondly is the date of our meeting today related to this forecast since it’s the first time we are summing up the year on a Friday. Putin: Is your name Christina? I’ll tell you, but it must remain exclusively between us. This is classified information. It’s our secret weapon, but we will only use it in the most extreme case because we are against deploying weapons in space. Seriously though, it’s a comet. Our scientists are aware of what is happening. Moreover, this is a comet from another star, so it behaves differently from comets of our galactic origin. It has a different shell and as it approaches closer to the Sun, slightly different processes occur on its surface, including in the field tail of this rocket. Things look different there, but it’s quite large. I think somewhere between 2 to 6 kilometers. Look, the moon is 400,000 kilometers away from us. And the object you are talking about is hundreds of millions of kilometers away. I don’t think it poses any threat to us. We’ll let it go to Jupiter. And at the beginning of next year, the comet will leave the solar system.” ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

A composite image of the interstellar object 3I/ATLAS, captured on November 6, 2025 by the Europa Ultraviolet Spectrograph instrument (UVS) on NASA’s Europa Clipper spacecraft, from a distance of 164 million kilometers. (Image credit: NASA/JPL-Caltech/SWRI)NASA’s Europa Clipper spacecraft observed the interstellar object 3I/ATLAS on November 6, 2025, from a distance of 164 million kilometers. During an observing period of seven hours, the Europa Ultraviolet Spectrograph (UVS) instrument recorded data on the abundances of various elements in the gas plume surrounding the nucleus of 3I/ATLAS. A false-color image was obtained by stacking the brightness maps at multiple UV wavelengths. The image is extremely valuable in constraining the anti-tail and tail geometry of 3I/ATLAS near perihelion. Europa Clipper observed 3I/ATLAS when Earth-based observations were largely blocked by the Sun’s position. With 3I/ATLAS passing between Europa Clipper and the Sun, the vantage point of Clipper’s observations provided a unique perspective. The sunward viewpoint provided a downstream view of the anti-tail and tail stemming out of the nucleus of 3I/ATLAS when it went close to the Sun. Europa-UVS detected the spectral fingerprints of oxygen, hydrogen and dust from the outgassing of 3I/ATLAS near perihelion. Europa Clipper was launched from Earth in October 2024, and is expected to arrive near Jupiter in April 2030, where it will study Jupiter’s frozen moon Europa — inside of which a subsurface liquid ocean might support life. Clipper will orbit Jupiter and perform 49 close flybys of Europa. Following the rendezvous with Europa Clipper, 3I/ATLAS will arrive closest to Jupiter as early as March 16, 2026, demonstrating how fast it is relative to a human-made spacecraft. In a TV interview today, I expressed my wish to board a fast interstellar traveler like 3I/ATLAS so that it would carry me out of the solar system faster than human-made spacecraft. Ad Astra! ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Image of the interstellar object 3I/ATLAS (top left panel) from a 0.25-meter telescope in Calabria, Italy, taken on December 15, 2025 at 1:58 UTC with 1.38 arcseconds per pixel — corresponding to 3,850 kilometers at the source distance. The other three panels show a brightness map at different wavelength bands centered on 0.658 [R], 0.53 (Green) and 0.445 (Blue) micrometers, using a Larson-Sekanina gradient filter. Their field of view spans 1.6 by 0.7 million kilometers and shows a prominent tightly-collimated anti-tail jet from 3I/ATLAS in the sunward direction, towards the bottom left corner. (Image credit: Toni Scarmato)My latest essay, available here, listed 15 anomalies of the interstellar object 3I/ATLAS. The following morning before my routine jog at sunrise, I had the following exchange with my esteemed colleague, the astrophysics Professor Josh Winn from Princeton University. He wrote: “Dear Avi, I’ve been following this story, and your interpretations, with interest and enjoyment. But there has been something bothering me and I finally feel moved to write you about it. To my knowledge, none of the anomalies were predicted, and hence, I cannot take seriously the very low probabilities that have been assigned to them. For example, it is interesting that the trajectory is nearly anti-aligned with the ecliptic, but it also would have been interesting if the orbital plane had been aligned, perpendicular to, exactly 45° from, …, the ecliptic. Or aligned with the Sun’s equatorial plane, or Pluto’s orbit, or Halley’s Comet … Or if the trajectory had pointed back to a known star, or the galactic center, or the anti-center, or the galactic poles, or the LMC, etc. It is interesting that the trajectory makes close passes to a few planets but not Earth, but it also would have been interesting if the trajectory made close passes to any subset of planets, or only to the Earth, or if it avoided any close approaches with planets despite being near the ecliptic. This problem is avoided if predictions are made in advance. Can we make definite predictions for the future behavior of the object under the hypothesis that it is technological? Did anyone predict that coming close to a planet’s Hill radius would be a sign of technological origin? Or that the nickel/iron ratio would be unusual? That jets would emerge in special directions? I remember reading about a prediction that the object would perform a certain maneuver near perihelion — can that be ruled out? Noticing anomalies is obviously important, but without trying to make and test predictions, there is something important missing. Best wishes, Josh” My reply was as follows: “Dear Josh, A predictable anomaly is an oxymoron, a contradiction in terms. The nature of an anomaly is that it is unexpected, an outlier. Quantum mechanics stemmed from anomalies of classical physics. And even after it was discovered, Albert Einstein insisted that quantum mechanics cannot have `spooky action at a distance’. When discovering new knowledge, we should not assume that our imagination is good enough to forecast this knowledge. When I started astrophysics 38 years ago, the possible existence of hot Jupiters was definitely not forecasted or included as a target to search for in the folklore of observers. Regarding my list of anomalies for 3I/ATLAS: the existence of nickel without iron is a result of the carbonyl pathway for the industrial production of nickel alloys. We have never seen it in comets so it is an anomaly. It is a technological signature in the same way that artificial light on the nightside of an exoplanet would be. When detectives arrive at the scene of a crime, your methodology would ask them to ignore unusual facts because they did not forecast them before arriving there. I say that this is the wrong approach to crack the mystery of the crime, and any practicing detective — including fictional ones like Sherlock Holmes, would have agreed with me. Happy Hannukah! Avi” Josh replied promptly: “Thanks, Avi, for taking the time to reply — and Happy Hannukah! I agree that it’s very important to notice anomalies and take them seriously. My point was that to convince oneself and other people of a hypothesis, one needs to go further — one must use the anomalies to construct theories that make predictions that are then confirmed. A problem with the hypothesis that 3I/ATLAS is of technological origin is that it is very flexible, because of the unknown goals and technologies involved, and can therefore be retrospectively considered compatible with just about any anomaly. I’d like to see some predictions that can be tested, and likewise, a list of possible observations that would rule out the possibility that 3I/ATLAS is of technological origin. Think about how the situation would differ if you’d written a paper a year ago with rational arguments that technological visitors would likely arrive on retrograde orbits and come to perihelion at solar opposition! Relatedly, I think the “a posteriori” probabilities that you refer to in various messages are misleading, because the statistical questions are constructed after already knowing the observations. The probability of interest is not “how likely is it that a random trajectory would be so close to retrograde” — rather, it is “how likely is it that a random trajectory will have any combination of parameters that can be regarded retrospectively as interesting”? The latter probability is difficult to calculate but is probably high. It’s like picking a random integer and then afterward trying to see if there’s anything interesting about it … it’s almost always possible to find something interesting (see, e.g., https://mathigon.org/almanac) If you disagree, would you like to make a bet with an odds ratio of (0.2%) * (0.5%) * (0.5%)² = 0.00000000025, the product of probabilities cited in your recent message, that the object will turn out to be of technological origin? That is, if it is of technological origin, I pay you $1, and if it is not of technological origin, you pay me $4 billion? I’ll lower the payout to $1 billion to make it even more enticing. Josh” In concluding our exchange, I wrote: “What you’d like to see in terms of a prediction is irrelevant as to the question of whether a conjecture is real. The fact that hot Jupiters were not predicted does not mean that the anomalies they represented in the minds of traditional thinkers were not real just because they were not predicted ahead of time. There is a sense of arrogance in the way you formulate the idea that we should predict or expect new knowledge. In fact, the most exciting aspect of science is the unknown unknowns, even though we usually fund projects that search for the known unknowns. The foundation of science is the humility to learn, not the arrogance of expertise. I am not claiming that 3I/ATLAS is technological but only stating that we should consider its anomalies with this possibility in mind.” Interestingly, the Chronicle of Higher Education published here a couple of days ago an article by Sally Satel titled: “Are Bad Researchers Bad People: The absence of humility, integrity and open-mindedness isn’t just a moral failure. It’s a methodological one.” The opening sentence of the article states: “Charles Darwin set a “golden rule” for his study of nature. Whenever he encountered information that ran counter to his ideas, he would make a note of it “without fail and at once.” Why? Because, as Darwin wrote in his autobiography, “such facts and thoughts were far more apt to escape from the memory than favourable ones.” In another passage, Sally writes: “In addition to epistemic humility, other virtues, as…, Intellectual Virtues, include open-mindedness, love of knowledge, and generosity (sharing intellectual goods), alongside such traits as ‘intellectual courage’ (willingness to consider difficult, unpopular, or counterintuitive ideas) and ‘intellectual firmness’ (the ability to balance one’s belief against letting go in the face of compelling evidence).” I rest my case, Josh. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Image of the interstellar object 3I/ATLAS (top left panel) from a 0.25-meter telescope in Calabria, Italy, taken on December 15, 2025 at 1:58 UTC with 1.38 arcseconds per pixel — corresponding to 3,850 kilometers at the source distance. The other three panels show a brightness map at different wavelength bands centered on 0.658 [R], 0.53 (Green) and 0.445 (Blue) micrometers, using a Larson-Sekanina gradient filter. Their field of view spans 1.6 by 0.7 million kilometers and shows a prominent tightly-collimated anti-tail jet from 3I/ATLAS in the sunward direction, towards the bottom left corner. (Image credit: Toni Scarmato)The near alignment of the rotation axis of the interstellar object 3I/ATLAS with the sunward direction at large distances (as discussed here and here) could have been spoiled after perihelion. The rotation axis can remain fixed if no torque acts on 3I/ATLAS. However, the direction of motion of 3I/ATLAS was shifted by the following angle (in radians) at perihelion: 2GM/(b*v²)= 0.286=16.4 degrees, where G is Newton’s constant, M is the mass of the Sun, b=202 million kilometers is the perihelion distance and v=68 kilometers per second is the perihelion speed. Remarkably, this deflection angle is twice the opening angle of the anti-tail jet, which was observed to span about 8 degrees out to a distance of order a million kilometers in the latest images of 3I/ATLAS from December 15, 2025 (as discussed here). If one edge of the jet’s cone overlapped with the sunward direction before perihelion, then the other edge of an identical jet cone on the opposite pole of 3I/ATLAS overlaps with the sunward direction after perihelion. As 3I/ATLAS approach perigee on December 19, 2025, the time is ripe to summarize all the anomalies of 3I/ATLAS, organized by themes: Geometric Coincidences: 1. The retrograde trajectory of 3I/ATLAS is aligned to within 5 degrees with the ecliptic plane of the planets around the Sun, with a probability of 0.2% (as discussed here). This suggests that the trajectory may have been planned. 2. The arrival time of 3I/ATLAS was fine-tuned to bring it to 29 and 54 million kilometers from Mars and Jupiter, respectively, and be unobservable from Earth at perihelion (as discussed here). 3. The forecasted perijove distance of 3I/ATLAS during its encounter with Jupiter on March 16, 2026 is 53.6 million kilometers, close to Jupiter’s Hill radius, 53.5 million kilometers (as discussed here). This match includes the non-gravitational acceleration that 3I/ATLAS displayed near perihelion. The rare coincidence might mean that 3I/ATLAS intends to release technological devices at Jupiter’s Lagrange points — where fuel requirements are minimal. 4. Analysis of the Hubble Space Telescope image from July 21, 2025 (as discussed here) suggests that the anti-tail before perihelion must have been in the form of a tightly collimated jet that is about ten times longer than it is wide. This is similar to the tight collimation observed in the latest post-perihelion images. It is difficult to understand how the sublimation of pockets of ice as a result of illumination by sunlight would lead to tightly collimated jets out to a million kilometers. No known comet exhibited a physical sunward jet of this length. For a technological object, a beam of particles might be used to mitigate the risk from the solar wind that would otherwise impact its surface at a relative speed of order 500 kilometers per second and release a hundred thousand times more energy per unit mass than explosives. 5. At large distances, the rotation axis of 3I/ATLAS was aligned to within 8 degrees with the sunward direction when it entered the solar system (as reported here). The probability for that is 0.5%. 6. The observed wobble of the pre-perihelion jet in the direction of the Sun (as reported here during July and August 2025) requires the base of the jet to be within 8 degrees from the sun-facing pole, with probability of 0.5%. 7. The existence of a prominent jet towards the Sun on the way of 3I/ATLAS out of the solar system requires a similar coincidence near the opposite pole of the rotation axis. The fact that a tightly collimated jet appears as the sunward anti-tail both before and after perihelion (while reversing direction at perihelion relative to the direction of motion), has a tiny probability of occurring at random, equal to the square of 0.5% or 0.000025. 8. The launch base of the post-perihelion anti-tail jet resided on the nightside of 3I/ATLAS before perihelion and the base of the pre-perihelion anti-tail jet is now on the nightside of 3I/ATLAS after perihelion. For these bases to be active only when facing the Sun, they must be well insulated on the nightside for a period longer than several months. However, heat would naturally flow by conduction throughout the body of a natural comet, making this insulation requirement difficult to satisfy. 9. The gravitational deflection of 3I/ATLAS by 16 degrees at perihelion, is exactly twice the opening angle of the anti-tail jet. This coincidence allows the wobbling jet around the rotation axis to generate an anti-tail in the direction of the Sun before perihelion and a counter jet on the opposite pole after perihelion, with a jet opening angle of 8 degrees on both poles. 10. 3I/ATLAS arrived from a direction coincident with the radio “Wow! Signal” to within 9 degrees, with a probability of 0.6% (as discussed here). Composition Anomalies of the Gas Shed by 3I/ATLAS: 11. The gas plume surrounding 3I/ATLAS contains much more nickel than iron, as found in industrially-produced nickel alloys, and a nickel to cyanide ratio that is orders of magnitude larger than for thousands of known comets, including 2I/Borisov (see here). This might indicate a technological origin for these abundances. 12. The gas plume surrounding 3I/ATLAS contains only 4% water by mass, whereas water is a dominant constituent in familiar solar-system comets (as discussed here). The plume might have resulted from the sunlight releasing the ices and dust that accumulated on the surface of a technological object during its journey through cold dense clouds of the interstellar medium. Unusual Physical Properties: 13. The nucleus of 3I/ATLAS is much more massive than 1I/`Oumuamua and 2I/Borisov, while moving faster than both (as discussed here and here). There might not be enough rocky material in interstellar space to deliver a natural iceberg of this mass once per decade to the inner solar system (as discussed here). This suggests that 3I/ATLAS may have targeted the inner solar system rather than being drawn at random from the reservoir of interstellar icebergs. 14. 3I/ATLAS shows extreme negative polarization, unprecedented for all known comets, including 2I/Borisov (as discussed here). This unusual polarization may be related to its unusual anti-tail. 15. Near perihelion, 3I/ATLAS brightened faster than any known comet and was bluer than the Sun (as discussed here). It is important to keep in mind that other technological civilizations could have used the foundation of a natural object to plant technological devices within it (as discussed here). Whether we encounter a “Trojan Horse” can be decided only through a careful study of the anomalies that distinguish 3I/ATLAS from familiar comets. As announced here, the International Asteroid Warning Network is conducting a Planetary Defense campaign to collect as much data as possible on 3I/ATLAS between November 27, 2025 and January 27, 2026. Once this data is made public, I will update my rank for 3I/ATLAS on the Loeb Classification Scale (as quantified here and here). In a new paper that I co-authored with the brilliant PhD student Oem Trivedi (posted today here), we provided the mathematical framework for updating the Loeb scale of interstellar objects over time. Irrespective of the true nature of 3I/ATLAS, my New Year’s resolution is simple. Starting on the early morning of December 19, 2025, I will keep looking up in the direction 3I/ATLAS during my future daily jogs before sunrise. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Images of the tightly-collimated anti-tail jet from 3I/Atlas in the sunward direction (lower left), as processed through a Larson-Sekanina gradient filter on December 15 (top) and 9 (middle), 2025 by Toni Scarmato, and on December 13, 2025 (bottom) by Teerasak Thaluang.My latest essay on the 14th anomaly of the interstellar object 3I/ATLAS (available here) focused on the alignment of its rotation axis with the sunward direction at large distances. The fact that a tightly collimated jet appears as the anti-tail in the direction of the Sun both before and after perihelion has a tiny probability of occurring at random, 0.000025. But the collimation of the jet to within 8 degrees out to a distance of half a million kilometers, as seen in the latest images of 3I/ATLAS from December 15, 2025 (and discussed here), is also a highly unlikely occurrence. My brilliant colleagues, Dr. Eric Keto and Dr. Frank Laukien, offered independently their important insights on this matter. Eric wrote: “The pre-perihelion anti-tail is a sunward jet located near the rotation axis that happens to align with the sunward vector. This makes it spin like a rifle bullet around its direction of travel which was sunward. There is no necessary connection between the jets on either side of perihelion.” The paper that Eric and I co-authored about the the Hubble Space Telescope image from July 21, 2025 (available here), concluded that the anti-tail before perihelion must be a tightly collimated jet that is about ten times longer than it is wide. This is because its long axis extends in the Hubble image towards the Sun twice as far as its width, but the jet is viewed from an angle of 10 degrees relative to its long axis — which adds an extra projection factor of [1/sin(10)]=5.8, making the actual length-to-width ratio about 11.6. Indeed, the latest images of 3I/ATLAS from this week show a sunward jet that is about ten times longer than it is wide, with an opening angle of order 6–8 degrees. What natural mechanism could explain a tightly-collimated anti-tail jet both before and after perihelion in the direction of the Sun? The rotation axis of 3I/ATLAS in July-August 2025 was aligned to within 8 degrees with the sunward direction according to a new report here. This implies that the base of the new anti-tail jet after perihelion must have been on the nightside of 3I/ATLAS before perihelion and the base of the old anti-tail jet must be in the nightside of 3I/ATLAS after perihelion. For them to be active only when facing the Sun, they must be well insulated on the nightside, a non-trivial 15th anomaly for a natural comet. Why would these independent bases near the opposite poles of the rotation axis both produce tight jets with an opening angle of order 6–8 degrees? Frank wrote: “Avi, Only a typical natural cometary tail (not anti-tail) could be tightly collimated by sunlight, since the Sun is essentially a point source from the point-of-view of the comet, and gas or dust that gets sublimated by sunlight into a full hemisphere of 2pi solid angle, then quickly gets pushed away in a tightly collimated comet tail by the solar wind and light. On the other hand, I cannot see how a tightly collimated natural anti-tail could get created: any large or object-covering ice field would generate a forward plume that would fill a 2pi solid angle, assuming an approximately spherical object and sublimation primarily in a direction that is orthogonal to the surface, and not primarily colinear with the incident sunlight. Hypothetically, a very deep ice pocket, shaped like a gun barrel, may emit a tightly collimated natural gas and dust beam, but the sunlight would only shine down that ‘gun barrel’ of a rotating object for a brief moment. If the collimated, modulated anti-tails pointing towards the Sun are technological, they could be: · for propulsion (doesn’t make sense), unless propulsion away from the Sun had some intentional navigational effects to achieve or avoid ‘something’, or · as directed weapons (doesn’t make sense after perihelion, as they no longer ‘clear the way’ of the object of debris), or · to create a directed shield against sunlight and solar wind to protect the technological object’s electronics or biological content or surface? Best wishes, Frank” As it turns out, I was just contemplating the last possibility in the context of a technological thruster before Frank’s message arrived. His insights are important. Observing 3I/ATLAS on a retrograde trajectory which is aligned to within 5 degrees with the ecliptic plane of the planets around the Sun was the initial trigger to consider a technological origin for it. The near alignment of its rotation axis with the direction of the Sun at large distances is another reason to consider this possibility. Finally, the appearance of tightly collimated anti-tails before and after perihelion add to the mystery. These are all rare geometric coincidences that cannot be easily brushed aside by NASA’s narrative at the press conference here that: “3I/ATLAS is definitely a comet with qualities that can be naturally explained by its different birth environment.” How can a different birth environment explain these geometric anomalies which are unique in reference to the Solar system orientation? NASA’s suggestion that “rare things happen” must attend to the fact that the probability for the 5-degrees trajectory-alignment with the ecliptic plane (0.002) times the probability for the 8-degrees rotation-axis alignment with the direction of the Sun at large distances (0.005) times the probability of two independent bases that produce tightly-collimated jets to within 8-degrees from the rotation poles (0.000025), gives a net probability of one part in 4 billion! This resulting probability of 0.00000000025 does not factor in other anomalies (as listed here), like the detection of much more nickel than iron as found in industrially producted nickel alloys. This raises two questions: 1. What is 3I/ATLAS? 2. Why are self-declared “comet experts” not curious about the first question. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

A 14th Anomaly of 3I/ATLAS: Alignment of Its Rotation Axis with the Sunward Direction at Large DistancesPhase angle of the position angle of the anti-tail of 3I/ATLAS, measured at a projected distance of 6,000 kilometers from the brightness peak and phased with the calculated 7.74 (± 0.35) hour period. The horizontal red line is the mean value of position angles, representing the sky-projected orientation of the rotation axis. (Image credit: Serra-Ricart, Licandro & Alarcon 2025)The new paper (accessible here) reporting the detection of a periodic wobble in the anti-tail jet of the interstellar object 3I/ATLAS during July and August, 2025, implies that the jet base is offset by less than 8 degrees from the poles associated with the rotation axis of the nucleus. As the nucleus rotates, the jet precesses along a cone surrounding this rotation axis. This suggests that at large distances from the Sun, 3I/ATLAS has a permanent dayside and a permanent nightside because its rotation axis is nearly aligned with the direction of the Sun. If the jet base has a simple natural origin from of a pocket of ice which is sublimated while being exposed to sunlight, the inferred geometry constitutes a new 14th anomaly for 3I/ATLAS in addition the 13 anomalies listed before here. The new anomaly relates to the small probability of the rotation axis of the nucleus of 3I/ATLAS being aligned to within 8 degrees with the direction of the Sun, when the interstellar object approached the Sun at a heliocentric distance larger than 5 times the Earth-Sun separation (AU). The chance of that alignment occuring at random is 0.005. If not for that special alignment, the anti-tail jet towards the Sun would have been oriented at a much larger angle relative to the rotation axis and would have shown a much larger wobble in position angle than the observed value of 8 degrees. With a larger misalignment angle, it could have featured prominent gaps in activity as its base exits the dayside and enters the nightside of 3I/ATLAS. Images of the interstellar object 3I/ATLAS. Thin purple lines indicate the position angle of the detected anti-tail jet at a projected distance of 6,000 kilometers from the brightness peak (dotted red circle). For each frame, the observation date and the start and end times in UTC are shown above the panels, along with the total number of sidereal-tracking exposures and the cumulative integration time. The projected velocity vector (red arrow) and the anti-solar direction (yellow arrow) are marked, as well as the image scale and orientation. Degraded orange lines denote the projected rotation-axis direction, derived from mean value of the anti-tail positions angles, while yellow lines trace the tail direction. Brightness contours are overplotted using ten logarithmically spaced levels between the 20th and 95th percentiles of pixel intensity in each frame. The anti-tail refers to the narrow, linear, black feature extending roughly northwest in the direction of the Sun. (Image credit: Serra-Ricart, Licandro & Alarcon 2025)This coincidence applies to the geometry of the anti-tail and the rotation axis of 3I/ATLAS before perihelion. However, the remarkable new revelation after its perihelion on October 29, 2025,gleaned from the latest images taken by the Hubble Space Telescope (as discussed here) and ground-based telescopes (as discussed here, here and here), is that 3I/ATLAS still shows a prominent anti-tail jet in the direction of the Sun. This is despite the fact that 3I/ATLAS is currently receding away from the Sun and its Sun-facing side used to be on its night-side when 3I/ATLAS was approaching the Sun in July-August 2025. The base that launched the anti-tail jet in July 2025 is now on the night-side of 3I/ATLAS. The comet interpretation of 3I/ATLAS requires a new pocket of ice near the opposite pole of the rotation axis, that gives rise to a prominent new anti-tail jet after perihelion. Since the new anti-tail is observed to be collimated to within 8 degrees out to half a million kilometers in the latest image of 3I/ATLAS — taken on December 15, 2025 (as discussed here), the proximity of the new jet base relative to the rotation axis and the Sun’s new direction raises the 14th anomaly to the second power. In other words, the chance of two major pockets of ice being located near the rotation poles of 3I/ATLAS, so that one of them would be on the dayside when 3I/ATLAS approaches the Sun from a great distance and the other is on the dayside when 3I/ATLAS is on its way out of the Solar system, while both being within 8 degrees of the nearest rotation pole when facing the Sun, is the square of 0.005 or a tiny probability of merely 0.000025. Of course, a technological spacecraft might have a reason for aligning the outflow of gas from its thrusters in the direction of the Sun. We do not have high-resolution images of the jet direction near perihelion. The tight collimation of the anti-tail out to a distance of half a million kilometers, larger than the distance to the Moon, despite the solar radiation pressure and wind after perihelion, raises new questions. Why does the sunward jet maintain its collimation without being broadened or pushed away from the Sun? What is its speed and mass loss rate? Hopefully, upcoming spectroscopic observations of the material it carries will clarify the launch mechanism of the anti-tail. The derived periodicity of 7.74 (± 0.35) hours in July-August 2025, could imply a nucleus rotation period of 15.48 (± 0.70) hours if the anti-tail originates from a single active spot at any given time. This value is indeed consistent with the rotation period derived during July 2025 from the periodic brightness variability of 3I/ATLAS: 16.16 (± 0.01) hours (as reported here) . For a nucleus radius of 2 kilometers with a rotation period of 15.5 hours, the centrifugal acceleration of the surface of 3I/ATLAS is 0.0025 centimeters per second squared. This value is tiny, just 2.6 millionths of the gravitational acceleration on the surface of Earth, 1-gee. The rotation period needs to be shortened to 1.5 minutes in order to create an artificial gravity similar to 1-gee. ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

Images of the interstellar object 3I/ATLAS. Thin purple lines indicate the position angle of the detected anti-tail jet at a projected distance of 6,000 kilometers from the brightness peak (dotted red circle). For each frame, the observation date and the start and end times in UTC are shown above the panels, along with the total number of sidereal-tracking exposures and the cumulative integration time. The projected velocity vector (red arrow) and the anti-solar direction (yellow arrow) are marked, as well as the image scale and orientation. Degraded orange lines denote the projected rotation-axis direction, derived from mean value of the anti-tail positions angles, while yellow lines trace the tail direction. Brightness contours are overplotted using ten logarithmically spaced levels between the 20th and 95th percentiles of pixel intensity in each frame. The anti-tail refers to the narrow, linear, black feature extending roughly northwest in the direction of the Sun. (Image credit: Serra-Ricart, Licandro & Alarcon 2025)A new paper (accessible here) reports the detection of a periodic wobble in the anti-tail jet of the interstellar object 3I/ATLAS with a period of 7.74 (± 0.35) hours during July and August, 2025. The wobble is the result of the anti-tail base (from where the jet is launched out of the nucleus) being offset from the poles associated with the rotation axis of the nucleus. As a result of this offset, the jet axis exhibits precession along a cone surrounding the rotation axis, just like the rotating light beam of a lighthouse or a pulsar. The paper analyses images of 3I/ATLAS from 37 nights between July 2 and September 5, 2025, taken by the Two-meter Twin Telescope (TTT) at the Teide Observatory in Tenerife, Canary Islands, Spain. The images show a faint high-latitude anti-tail of 3I/ATLAS which maintains an almost, though not perfectly, constant position angle. Accurate measurements of the position angle of the jet at a projected distance of 6,000 kilometers from the brightness peak, reveal a periodic modulation consistent with a high-latitude jet undergoing precession around the rotation axis of the nucleus. This is the first periodic jet-angle modulation detected in an interstellar object. The derived periodicity of 7.74 (± 0.35) hours may imply a nucleus rotation period of 15.48 (± 0.70) hours if the anti-tail originates from a single active spot near one of the poles associated with the rotation axis. This value is consistent with the period derived during July 2025 from the periodic brightness variability of 3I/ATLAS: 16.16 (± 0.01) hours (as reported here) . Phase angle of the position angle of the anti-tail of 3I/ATLAS, measured at a projected distance of 6,000 kilometers from the brightness peak and phased with the calculated 7.74 (± 0.35) hour period. The horizontal red line is the mean value of position angles, representing the sky-projected orientation of the rotation axis. (Image credit: Serra-Ricart, Licandro & Alarcon 2025)At 06:02 UTC (01:02 AM US Eastern Time) of Friday, December 19, 2025, 3I/ATLAS will get to a perigee distance of 268.9097 (± 0.0060) million kilometers. Coincidentally, this night is also a New Moon, and so mother Nature is kind enough to allow Earthlings to watch 3I/ATLAS without the contamination of moonlight. The data collected around that time by multiple telescopes on Earth and in space will educate us about the qualities of our latest interstellar visitor. *** The appeal of 3I/ATLAS to people of all backgrounds was demonstrated in two new messages that I received today before my morning jog at sunrise. Letter 1: “Dear Professor Loeb, My name is Carlos Mendoza. I am writing to you from the Chilean, Patagonia — often called the “End of the World.” Here, under some of the darkest and most pristine southern skies on Earth, your recent analysis of the interstellar object 3I/ATLAS resonates deeply Your relentless pursuit of the truth, regardless of established consensus, is a source of great inspiration here at the southern edge of the continent. Living in such a remote landscape teaches us that reality is often stranger and more vast than we assume. Your courage to challenge scientific dogma encourages us to look up with the same sense of wonder and possibility. Thank you for reminding the world that science should be an adventure into the unknown, not just a defense of the known. Sincerely, Carlos Patagonia, Chile” Letter 2: “Hi Avi, After we spoke, two historical examples came to mind about paradigms determining perception (or at least interpretation): Because of Aristotelian cosmology that held that the sun was perfect, early astronomers were positive that sunspots were satellites (it was easier for them to reach that clumsy conclusion rather than offer the most straightforward interpretation of what they observed). U.S. radar operators detected the Japanese planes on the morning of December 7, 1941, but the aircraft were interpreted as expected B-17 bombers from California, because the American threat model did not include a Japanese attack on Pearl Harbor. Both illustrate a greater attachment to the received hypothesis than to data. I take it this is your concern with the insistence on seeing 3I/Atlas as a natural comet before all data is collected. Warmly, Nir — Nir Eisikovits Ph.D., L.L.B Professor of Philosophy Director, Center for Applied Ethics umb.edu/ethics UMass Boston” ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article

The top panel shows an image of 3I/ATLAS, taken on December 15, 2025 at 02:28:12 UTC on a 0.25-meter telescope in Calabria, Italy. The bottom panel includes the brightness map from a Larson-Sekanina rotational gradient filter on a fraction of the entire field of view, spanning 0.86 by 0.39 million kilometers and featuring an anti-tail going out to half a million kilometers from 3I/ATLAS in the sunward direction towards the lower left. (Image credit: Toni Scarmato)As of December 15, 2025, the interstellar object 3I/ATLAS arrived at a distance of about 270 million kilometers from Earth. By December 19, 2025, it will get to a perigee distance of 268.9 million kilometers, only 0.4% closer than it is today. The data collected by numerous observatories on Earth and in space will inform us in the coming weeks on the nature of 3I/ATLAS. The latest images from December 14 and 15, 2025 show a prominent anti-tail that extends out to half a million kilometers away from the nucleus of 3I/ATLAS towards the Sun. This length is larger than the average distance to the Moon: 384,400 kilometers. An anti-tail of this size had never been observed before for a comet. To reach a scale of 500,000 kilometers over the past 45 days after perihelion, the sunward speed of the material in the anti-tail must be at least 130 meters per second relative to the nucleus of 3I/ATLAS. Whether this speed can be maintained by sublimated dust or gas from pockets of ice facing the solar wind and solar radiation pressure remains to be studied. The alternative is a jet from a technological thruster. An image of 3I/ATLAS, taken on December 14, 2025, with a total integration time of 2 hours and 22 minutes and no filter on a 14-inch (0.356-meter) telescope in June Lake, California. The field of view displayed in the bottom panel spans 4.24 million kilometers on a side. A green-blue anti-tail is pointing in the sunward direction towards the lower left. (Image credit: Dan Bartlett)How unusual are the properties of the anti-tail displayed by 3I/ATLAS? We do not have a good census of the population of interstellar objects, including any traffic of technological objects through the inner solar system. Our state-of-the-art survey telescopes, such as PanSTARRS, ATLAS or Rubin, can only detect reflection of sunlight from objects that are larger than 100-meters in diameter, roughly the size of a football field, within a distance comparable to the Earth-Sun separation. This diameter is an order of magnitude bigger than the largest spacecraft that humanity launched so far. In addition, existing astronomical surveys would miss near-Earth objects that travel much faster than tens of kilometers per second, the typical speed of asteroids or comets. In order to assess whether an interstellar object is an outlier that deserves a high rank on the Loeb Classification Scale — discussed here, here and here, we need to know the probability distribution functions for its properties. Our assessment will be more reliable as the sample of interstellar objects gets larger. The challenge is familiar for those who seek a partner from a small pool of dating candidates, as it is difficult to decide how exceptional any of the early dating candidates are until we sample a large number of them. Our interstellar dating pool might go beyond what Science Fiction writers imagine. Enrico Fermi’s question: “Where is everybody?” is often asked by lonely people. Our best advice to them is to engage in the search. Position of 3I/ATLAS relative to Earth and Jupiter on December 15, 2025. (Image credit: JPL Horizons)Earlier today, I received the following uplifting message from a young person who indeed wishes to engage in the search for interstellar technological objects: “Dear Professor Loeb, My name is Rúben, and I am writing to you today from Portugal to express my sincere admiration for your work and your courage in pushing scientific curiosity beyond conventional limits. Your approach to open, evidence driven inquiry has been truly inspiring to me. Since I was young, I was fascinated by space and even though I have never got a degree as a scientist or similar, I grew up seeking cosmic awareness and knowledge just because I was so interested in it all the time. And so, I am writing to you today from Portugal hoping that I could somehow be working on something that can make a difference for humanity in the future, as I want to be a part of that movement and work. That being said, I would be honored to contribute to your mission in any way possible. While I am not an academic researcher, I bring strong technical, analytical and creative skills, including software development, data handling, and digital communication, and I am fully willing to dedicate my time and effort to support your work where I may be useful, as my love for the greater purpose it has, is immense. If there is any opportunity to assist, collaborate, or contribute directly or indirectly I would be very grateful to learn how I could be of help. Thank you for your time and for the impact your work continues to have. Kind regards, Rúben” ABOUT THE AUTHOR (Image Credit: Chris Michel, National Academy of Sciences, 2023)Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024. View the full article