Avi Loeb: Did 3I/ATLAS Just Break-Up Near the Sun? 10.11.2025

• Did 3I/ATLAS Just Break-Up Near the Sun?
  by https://avi-loeb.medium.com/
  Let me start this quantitative discussion with the conservative assumption that the interstellar object 3I/ATLAS is a natural comet, and work out its properties based on its latest post-perihelion image.
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  The large-scale image of 3I/ATLAS reported here on November 9, 2029 shows multiple jets reaching out to ~1 million kilometers towards the Sun and ~3 million kilometers in the opposite direction, as discussed here.
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  For a natural comet, the outflow velocity of the jets is expected to be 0.4 kilometers per second, of order the sound speed of gas at the distance of 3I/ATLAS from the Sun. At that speed, the jets must have persisted over a timescale of 1–3 months.
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  Given that the jets towards the Sun were stopped by the solar wind at a distance of a million kilometers, I calculated here that their mass density is a few million proton masses per cubic centimeter at a distance of a million kilometers from 3I/ATLAS. The product of this mass density and the outflow speed, implies a mass flux of 5 billion tons per month per area of a million-kilometer on a side. I calculated here that the total mass associated with 3I/ATLAS is at least 33 billion tons based on its early dynamics. Adopting an outer surface area for the jetted material of order a million-kilometer squared, I find that 3I/ATLAS may have lost ~16% of its mass. This is consistent with the mass fraction required by its non-gravitational acceleration at perihelion, as I calculated here.
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