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An image of 3I/ATLAS, taken on November 22, 2025 at 19:25 UTC with a 0.5-meter telescope. At that time, 3I/ATLAS was close in projection to the galaxy NGC4454 in the sky. The sunward direction is towards the lower left corner. (Credit: Mitsunori Tsumura)

A number of images of the interstellar object 3I/ATLAS were taken on November 22–24, 2205 by amateur astronomers and astrophotographers. They consistently show a glowing coma with tightly-collimated anti-tail and tail.

The best image (available here) was taken by Mitsunori Tsumura on November 22 at 19:25 UTC with a 0.5-meter telescope. Given the current distance of 3I/ATLAS from Earth of 300 million kilometers, its tail appears to extend out to 5 million kilometers whereas the sunward anti-tail extends out to about a million kilometers. It takes a month to cross a million kilometers at a speed of 400 meters per second.

The huge extent of the anti-tail towards the Sun implies that it carries a large enough momentum flux to penetrate through the solar wind. The anti-tail’s ram-pressure exceeds that of the solar wind out to that distance. The solar wind is flowing at a speed of about 400 kilometers per second, which is at least a thousand times faster than the thermal speed of outflowing gas from a natural comet at the location of 3I/ATLAS. Since ram-pressure scales as the gas speed squared, this means that the outermost mass density in the anti-tail is a million times bigger than the solar wind density of a few proton masses per cubic centimeters. For a natural comet, the outermost mass density of the anti-tail implies a mass flux of 200 tons per second per square area of size 0.3-million kilometer on a side. Counting also the tail, this yields a total mass loss rate of about a few billion tons over the past two months.

For a natural comet, the estimated mass loss over the months of October and November 2025 is about 10% of the minimum mass associated with 3I/ATLAS, 33 billion tons — that I calculated here based on the lack of non-gravitational acceleration during the months of July, August and September 2025. Any such acceleration would stem from the anisotropy in the mass loss rate times the outflow speed, divided by the object mass. Since then, a non-gravitational acceleration was actually measured around perihelion in October 2025. By now its detection, reported here by JPL Horizons, is statistically significant at ten standard deviations. Momentum conservation at the maximum thermal gas speed of 400 meters per second implies that the measured level of non-gravitational acceleration requires more than 10% of the mass of 3I/ATLAS to be lost if it is a natural comet, as I showed here. Jets from technological thrusters could be more effective in accelerating 3I/ATLAS with less mass loss, as they produce higher exhaust speeds. The required mass loss to penetrate through the solar wind is scaled down by the square of the increased outflow speed. This corresponds to 2 or 4 orders of magnitude reduction in mass loss for chemical thrusters or ion thrusters, respectively. Future spectroscopic measurements could assess the speed of the jets and distinguish between the natural sublimation of pockets of ice by sunlight and technological alternatives.

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An image of 3I/ATLAS, taken on November 21, 2025. (Credit: Paul Craggs)

The unusually elongated appearance of 3I/ATLAS, as reported here by Paul Craggs on November 22, 2025, might have resulted from motion smearing of the image.

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An image of 3I/ATLAS, taken on November 22, 2025 at 5:28 UTC with a 0.315-meter telescope in Spain. (Credit: Peter Carson Leigh)

Two other images consistent with the anti-tail/tail morphology were taken by Peter Carson Leigh at 5:28 UTC on November 22, 2025 with a 0.315-meter telescope in Spain and by Elena Walter at 8:05 UTC on November 24, 2025 with a 0.432-meter telescope in Chile.

We are all awaiting better images from the largest telescopes on Earth, as well as from the Hubble and Webb Space Telescopes, near 3I/ATLAS’s closest approach to Earth on December 19, 2025 at a minimum distance of 269 million kilometers.

The best is yet to come. The data collected in December 2025 will set the verdict on the nature of 3I/ATLAS. In addition, we will be able to assess whether 3I/ATLAS is forecasted to reach the Hill radius of Jupiter on March 16, 2025 — as discussed here, to better than four significant digits.

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An image of 3I/ATLAS, taken on November 24 at 8:05 UTC with a 0.432-meter telescope in Chile. (Credit: Elena Walter, Liena Dreams)

ABOUT THE AUTHOR

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(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.

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      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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