Avi Loeb: 3I/ATLAS Anomalies and Missing Cometary Tail

• No Clear Cometary Tail in Post-Perihelion Images of 3I/ATLAS
  by https://avi-loeb.medium.com/
  On November 5, 2025, two new images of the interstellar object 3I/ATLAS were released. They show a compact source of light without a clear cometary tail. The coma is not very different in morphology than its appearance in the Hubble Space Telescope on July 21, 2025 (accessible here).
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  This is surprising in view of NASA’s JPL report here of a non-gravitational acceleration — normalized at a heliocentric value of 1 au:
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  1. A radial acceleration away from the Sun of 1.1×10^{-6} au per day squared.
  2. A transverse acceleration relative to the Sun’s direction of 3.7×10^{-7} au per day squared.
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  Based on momentum conservation (as discussed here), I derived here that the mass fraction lost during the perihelion passage of 3I/ATLAS is larger than 13%. For a typical comet, this should have resulted in a massive coma with dust and gas that would have been pushed by the solar radiation pressure and the solar wind to the shape of a typical cometary tail pointing away from the Sun. No such tail is visible in the new images from November 5, 2025.
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  In comparison, I include below an image of the solar system’s comet Lemmon, taken by one of the telescopes that observed 3I/ATLAS two days ago. Lemmon features a clear cometary tail pointing away from the Sun, as expected.
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