Our interstellar friend is behind the Sun (to observers on or near Earth). Good time to recap activity (emission of coma and tail(s)) so far:
Astrophysics > Earth and Planetary Astrophysics arxiv.org/abs/2510.18769
[Submitted on 21 Oct 2025]
Jewitt, D. Luu, J. Pre-perihelion Development of Interstellar Comet 3I/ATLAS
Using ‘just’ the Nordic Optical Telescope (an older, moderate-aperture asset), Jewitt and Luu followed ATLAS from soon after discovery, to September. Emissions rose as the comet neared the inner Solar System, and warmed. 3I is, clearly, not a grand, showy comet; its emission of water is a bit low for such bodies. Dust is also low- in the literal sense. The IAU defines dust particles as being tiny- on the scale of microns. Instead, 3I appears to be shedding more micrometeoroids, defined as submillimeter-scale and larger. This, too, is not average yet not bizarre. Comet Encke also emits most of its solids in the form of larger grains, not as microscopic motes. “Similarly large particles were earlier inferred in 2I/Borisov (Kim et al., 2020) and are common in weakly active comets and active asteroids. A possible explanation for the dominance of large particles is that smaller particles are more tightly bound by inter-particle forces and cannot be so readily detached”.
Again, fair warning for papers posted via arXiv. I will say, though, that nothing here is an extraordinary claim, demanding extraordinary evidence as they say. Conversely, Jewitt and Luu are well-regarded researchers with two bodies of work; they have a lot to lose by putting out junk.