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.

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.

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.