The Continuing Saga of Anti-Tails and Tails around 3I/ATLAS
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By CosmicSignals
The more I read about Enceladus, the more I find it puzzling that we aren't talking about it more when it comes to the search for extraterrestrial life. The fact that this moon has liquid water beneath its icy surface is such a compelling lead for astrobiologists. Water is a fundamental ingredient for life as we know it, yet discussions often overlook this fascinating world while focusing on Mars or Europa.
The plumes of water vapor that erupt from Enceladus’ south pole are also intriguing. They contain organic molecules that could serve as building blocks for life. It makes me wonder whether we should be prioritizing missions to study these plumes more closely. Could we find biosignatures or even microbial life in those ejecta?
I’ve read that some scientists believe the ocean beneath Enceladus’ ice could be in contact with a rocky seafloor, which would provide the necessary chemical reactions for life. It’s almost as if this moon is a hidden ocean world that hasn't fully revealed its secrets yet. What do you make of the idea that we might already be missing opportunities to investigate?
There’s also the argument that if life exists there, it could be so different from what we know that it wouldn’t even register on our current detection methods. The concept of alien life in extreme conditions has become more accepted, but still, the silence is deafening. If Enceladus is indeed harboring life, how might it communicate, or even interact with us?
Given the technological advancements in astrobiology, do you think missions to Enceladus should be ramped up? Or are we still too far from making any concrete discoveries? The potential discoveries that await beneath its icy crust could change everything we know about life in the universe.
I can't help but feel a sense of urgency about exploring these outer moons. If one day we do confirm life on Enceladus, the implications for our understanding of life elsewhere would be monumental. It’s as if we’re on the brink of a major discovery, yet we’re still holding back. What if we discover that life is more common in our solar system than we ever imagined?
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By Avi Loeb Medium
A 1.5-Solar-Mass Star in a Tight Orbit Around the 4.3-Million Solar-Mass Black Hole at the Milky-Way Center
Time series of the orbits of various stars around the supermassive black hole, SgrA*, at the Milky-Way center, obtained from data by GRAVITY/VLT between 2021 to 2025. The new star S301 arrives within 140 Schwarzschild radii of the black hole where its peak velocity is 8.3% of the speed of light, 25,000 kilometers per second. (Image credit: Abd El Dayem et al. 2026)The fastest moving star, labeled S301, was discovered recently by Stefan Gillessen’s team at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany (as first reported here, with the full paper accessible here). The star was discovered by near-infrared interferometry on 8-meter telescopes, using the GRAVITY instrument in operation at the European Southern Observatory’s (ESO’s) Very Large Telescope (VLT). Last night, I sat next to Stefan at the reception dinner of the annual conference of Harvard’s Black Hole Initiative, for which I served as the founding director a decade ago.
This 1.5-solar-mass star moves on a highly elliptical orbit with a period of 8.7 years and eccentricity of 0.98 around the supermassive black hole at the Milky-Way center, called Sagittarius A*. This black hole has a long history of swallowing 4.3 million solar masses of gas and stars from its environment. The peak velocity of S301 is 25,000 kilometers per second or 8.3% of the speed of light, as it comes down to a distance of 140 times the Schwarzschild radius of the black hole — which defines the scale of the black hole mouth from where even light cannot escape. If the star were to pass ten times closer to the black hole, it would have been ripped apart by tidal gravity into a stream of gas that shines brightly as it feeds the mouth of this spacetime beast.
The orbit of S301 can be used to test expectations from Albert Einstein’s formulation of gravity as the curvature of spacetime. Einstein’s equations predict that S301’s orbit will precess in response to the spin of the black hole, offering a precise new way to measure how fast Sagittarius A* is rotating within the coming decade.
How did this star get so close to the black hole?
A natural mechanism, proposed by Jack Hills in a 1988 paper published here, is the tidal break-up of a pair of stars by the black hole. About half of solar-mass stars form in binaries. When a binary star system gets close enough to the black hole, the tidal gravity becomes strong than the gravitational binding of the two stars and breaks the binary apart, sending one star out at a speed of up to thousands of kilometers per second and launching the second star into a tighter orbit around the black hole. Indeed, a population of hypervelocity stars had been discovered on their way out in the Milky-Way halo by Warren Brown and collaborators from the Harvard-Smithsonian Center for Astrophysics (as reported here).
In a 2006 paper published here, I proposed with the student, Idan Ginsburg, that the former companions of the observed hypervelocity stars in the Milky-Way halo might have produced the observed population of close-in S-stars on highly eccentric orbits around Sagittarius A*. The Galactic center star S301 is likely one of them, formed via the Hills mechanism out of an initial binary star system with an orbital period of 1–2 weeks over the past 100 million years.
In a follow-up paper published here, I showed with Idan that planets could survive the break-up of binary star systems by Sagittarius A*. As a result, Galactic travel agencies could sell tickets for thrilling journeys on habitable planets around hypervelocity stars. I wonder whether adventurous Galactic passengers would prefer to travel with a hypervelocity star on its way out of the Milky-Way galaxy at a speed of up to 1% of the speed of light or travel with a star like S301 as it reaches 8.3% of the speed of light and gets within a distance of 140 Schwarzschild radii from the largest black hole in our Galaxy. I would personally favor the latter, since the extreme spacetime structure of a supermassive black hole is far more exhilarating than the rarefied environment of intergalactic space. The trip close to the black hole also offers health benefits, since aging slows down by a third of a percent at closest approach of S301 to Sagittarius A*. This corresponds to a gain of 5 minutes to the passenger’s lifespan every day relative to distant relatives.
The black hole tour with S301 offers a view of the black hole’s mouth from a distance where it occupies roughly the same angle as the Moon or the Sun on our sky. The gas swirling into the event horizon of Sagittarius A* glows bright but at the center of this glow, there is a silhouette — a shadow cast by the absorption of light emanating behind the black hole. Over the decade between 2006 and 2016, I wrote 30 papers in collaboration with my postdoc, Avery Broderick, forecasting the expected portrait of a black hole (as detailed here and summarized for the general public here). By now, Sagittarius A* was imaged by the Event Horizon Telescope (here), whose headquarters was established at Harvard’s Black Hole Initiative during my directorship.
On a tour with S301, it would be fascinating to observed the silhouette image of Sagittarius A* from a minimum distance that is 140 million times closer than the Earth is from the black hole. I would have loved to serve as the tour guide on such a journey. Here’s hoping that Galactic travel agents would pay attention to this essay.
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.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
Social media:
https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb
https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb
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By USH
The video opens with a compilation of various types of unidentified flying objects. Among the strange sightings are cylinder-shaped UFOs and a so-called “Fastwalker,” but the most striking moment features an orange sphere off the coast of Encinitas, California.
The sphere suddenly appears above the ocean’s surface, casting an orange reflection across the water. It moves back and forth in a controlled manner before abruptly diving beneath the surface and vanishing.
Moments later, it reemerges, only to submerge again. While underwater, its movement is still visible through a series of flashes, until it suddenly bursts back out of the ocean once more.
This sequence repeats again, until the sphere finally ascends into the sky and disappears over the horizon.
This brief compilation suggests that a wide variety of advanced technologies, whether man-made or of extraterrestrial origin, may be operating around our planet, often just beyond our understanding.
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By Avi Loeb Medium
The so-called Hertzsprung–Russell diagram of 23,000 stars from the Hipparcos and Gliese catalogues, shows stellar luminosity versus color ranging from hot blue-white stars on the left side to cooler red stars on the right side. Hydrogen-burning stars like the Sun populate a band running from top-left to bottom-right called the Main Sequence. Giant stars clump on the upper-right side. At the lower-left is the band of white dwarfs, the dead cores of old stars that cool slowly over billions of years towards the bottom-right. (Image credit: Wikimedia)In my previous essay, posted here, I suggested that to preserve the habitability of its home planet — an advanced technological civilization might choose to move the planet away from a brightening sun-like star. The preferred planet-star separation would scale as the square root of the evolving star’s luminosity.
If this idea happens to be popular among our siblings in the family of intelligent civilizations within the Milky-Way galaxy, it might lead to an over-abundance of Earth-mass planets in the habitable zone around old Sun-like stars, as these stars evolve along the red giant branch of their Hertzsprung-Russel diagram.
But as the host sun-like star eventually turns to a faint white dwarf, the resident civilization might choose to migrate its planet closer to the dimmed furnace. This would imply an artificial over-abundance of habitable Earth-like planets around white dwarfs.
The graveyard of the Milky-Way galaxy is full of billions of corpses of dead sun-like stars in the form of old white dwarfs, each carrying about 60% of the mass of the Sun. At their typical age of a few billion years, the surface temperature of these white dwarfs is similar to that of the Sun, about 6,000 degrees Kelvin, resulting in white light which is conducive for life-as-we-know-it. The size of a white dwarf is comparable to that of Earth, but the habitable zone around it, is a hundred times bigger — amounting to 1 to 3 times that current radius of the Sun. Closer than a solar radius, the gravitational tide from the white dwarf would destroy a rocky planet.
The fact that the size of the white dwarf is comparable to that of Earth makes transits easy to detect. The probability for a transit is of order 0.6% for a habitable Earth-like planet around a white dwarf. This offers a unique opportunity for probing the composition of the atmospheres of habitable-zone Earth-mass exoplanets that transit white dwarfs.
In 2013, I co-authored a paper with Dani Maoz (published here) which showed that during a transit by an Earth-mass planet across a white dwarf, the transmission spectrum of the planet’s atmosphere would show prominent bio-markers such as molecular oxygen absorption at a wavelength of ∼ 0.76 micrometers. We calculated that a potentially life-sustaining Earth-like planet transiting a white dwarf would be detectable by the Webb telescope in about 5 hours of total exposure time, integrated over 160 two-minute transits.
A follow-up paper that I co-authored in 2014 here with my then undergraduate student Henry Lin (currently a professor at Princeton University), showed that industrial pollution is also detectable in habitable Earth-like planets around a white dwarf. In particular, tetrafluoromethane (CF4) and trichlorofluoromethane (CCl3F) are the easiest to detect chlorofluorocarbons (CFCs) resulting from technological activity. Our paper estimated that a few days of total integration time on the Webb telescope will be necessary to detect the concentration of CCl3F or CF4 for industrial pollution that is ten times higher than the current level on Earth.
The discovery of an over-abundance of habitable Earth-like planets around red giants or white dwarfs can be substantiated as a technological signature by finding industrial pollution in the related planetary atmospheres.
Finding such evidence would provide a useful guide to humanity on how to survive on Earth in the next 10 billion years, both before and after the Sun will turn into a red giant and then a white dwarf in 7.6 billion years (as calculated here).
Based on the census of white dwarfs reported here, most stars formed billions of years before the Sun. Given that we arrived late to the cosmic party, we might have missed numerous tragic incidents involving the extinction of civilizations which did not engage in a cosmic engineering project to save their planet before it lost habitability. We were not around to hear their cry for help. We better be wise to learn the lessons from the surviving civilization by studying habitable planets around red giants and white dwarfs.
As the philosopher George Santayana stated in his 1905 book titled The Life of Reason: Reason in Common Sense: “Those who cannot remember the past are condemned to repeat it.”
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.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
Social media:
https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb
https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb
View the full article
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By Avi Loeb Medium
A symmetric structure of three equally-separated jets is apparent near the nucleus of 3I/ATLAS, after applying the Larson-Sekanina rotational gradient filter to two exposures by the Hubble Space Telescope on 2025–12–27 UT. Two of the jets, separated by about 120 degrees, are prominent in both images, but their structure broadens into a wider fan on the right panel. Such morphological changes modulate the amplitude of the brightness variability. (Image Credit: T. Scarmato and A. Loeb 2026)In a new paper (accessible here) that I co-authored with the Italian observer Toni Scarmato, we use images from the Hubble Space Telescope to study the motion of the symmetric system of three jets around the nucleus of the interstellar object 3I/ATLAS.
The Hubble images were processed through a Larson–Sekanina rotational-gradient filter -which removed the circularly symmetric glow around the nucleus. The remaining brightness map shows three close-in jets in addition to a sunward anti-tail on a much larger scale, as discussed in our previous paper here.
These post-perihelion Hubble Images were taken between November 30 and December 27, 2025. The most prominent jet among the three is directed opposite to the Sun and appears to wobble over a period of 7.20 (± 0.05) hours. The total brightness shows contemporaneous variability with a period of 7.136 (±0.001) hours and an amplitude of about 30%. We interpret the characteristic post-perihelion period of about 7.1 hours as an attitude precession or nutation associated with a misalignment of the rotation axis with the symmetry axes of the nucleus. The wobble around the rotation axis displays a characteristic angular excursion of order 20 degrees, while the rotation axis is aligned with the sunward direction to within 20 degrees.
The right panel shows the schematic geometry of the 3-jet system near the nucleus of 3I/ATLAS (excluding the prominent anti-tail outflow towards the Sun), based on the filtered Hubble brightness map on the left. The projected spin axis in the sunward direction appears at a position angle of PA= 110 degrees, and the anti-sunward direction is at PA= 290 degrees. The PAs and oscillation half- amplitudes of the 3 jets are as follows: Jet 1: 55 (± 12.8) degrees; Jet 2 (sunward): 290 (± 20) degrees; Jet 3: 170 (± 12.6) degrees. The anti-sunward jet at PA=290 degrees wobbles with period of 7.2 hours. (Image Credit: T. Scarmato and A. Loeb 2026)Based on the inferred diameter of 2.6 kilometers for the nucleus of 3I/ATLAS (as reported here), only about a percent of the brightness of 3I/ATLAS originates from the reflection of sunlight by its nucleus. When rotation is misaligned with the symmetry axes of the nucleus, it can produce quasi-periodic wobbles and a non-sinusoidal variability. The new analysis links the inferred 7.1-hour period to an attitude precession or nutation of the multi-jet system. The brightness variability tracks transitions between collimated and fan-like morphologies of the jets.
The phase-folded light curve of 3I/ATLAS shows a period of about 7.14 hours. (Image Credit: T. Scarmato and A. Loeb 2026)Whereas the position angle of the most prominent jet shows variability with a period of 7.20 (± 0.05) hours, shorter periods are also apparent. Jets 2 shows a period of 2.9 hours and Jet 3 shows a period of 4.3 hours. The sum of 2.9 plus 4.3 is 7.2 hours.
The phase-folded variability of the position angle of Jet 2 shows a period of about 2.9 hours. (Image Credit: T. Scarmato and A. Loeb 2026)The phase-folded variability of the position angle of Jet 3 shows a period of 4.3 hours. (Image Credit: T. Scarmato and A. Loeb 2026)Summary of the inferred periods in the wobble of the jet system around 3I/ATLAS. (Image Credit: T. Scarmato and A. Loeb 2026)We interpret the ~7.1-hour periodicity as the result of the rotation of 3I/ATLAS being misaligned with the principal symmetry axes of its nucleus. The jet structure undergoes a quasi-periodic wobble as the nucleus exhibits precession and nutation about the rotation axis. This interpretation explains the orientation oscillations of the jets with morphology-dependent amplitudes and phases, the non-sinusoidal variability, and the sensitivity of the lightcurve to evolving collimation (fan opening) of the jets.
Multiple jets in different directions tend to balance each other and stabilize the rotation of 3I/ATLAS. Jet 2 — which is oriented approximately opposite to the Sun and close to the projected rotation axis — anchors the large-scale geometry, whereas Jets 1 and 3 trace the precession cone through their position angle oscillations. The wobble and changing collimation of the jets modulates both the projected jet directions and the total brightness.
The fundamental question that remains unresolved is whether the symmetric triple-jet system is a signature of technological thrusters or the sublimation of natural pockets of ice on the surface of a natural rocky iceberg.
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.
Professional website:
https://lweb.cfa.harvard.edu/~loeb/
Social media:
https://avi-loeb.medium.com/
https://www.youtube.com/@ProfessorAviLoeb
https://open.spotify.com/show/1zhndXkvSY2b8FdjspFpCd
https://x.com/ProfAviLoeb
View the full article
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