We’ve gone a little while without ATLAS matters:
Astrophysics > Earth and Planetary Astrophysics arxiv.org/abs/2508.15768
[Submitted on 22 Aug 2025]
Eubanks, T. M. Bills, B. G. Hibberd, A. et al. 3I/ATLAS (C/2025 N1): Direct Spacecraft Exploration of a Possible Relic of Planetary Formation at “Cosmic Noon”
arXiv:2508.15469
[Submitted on 22 Aug 2025]
Lisse, C. M. Bach, Y. P. Bryan, S. et al. SPHEREx Discovery of Strong Water Ice Absorption and an Extended Carbon Dioxide Coma in 3I/ATLAS
More arXiv papers on our interstellar friend (all the usual caveats apply). I have been noting the SPHEREx mission (Spectro-Photometric Ices and Epoch of Reionization Explorer) on this blog in general; now we see why SPHEREx is worthy and contributing. Viewing in the near-and mid-infrared, the space telescope can see molecular lines that are difficult or futile from ground telescopes. Here, the mission sees both water and hypervolatiles (components which boil before water) at 3I/ATLAS. If this had been attempted from the ground (not an airplane or balloon), the water and carbon dioxide spectral lines would be too close to each other, resulting in ambiguous data. Well, SOFIA has been grounded and dismantled, and apparently there’s no balloon flight this summer that can point to ATLAS. Either way, the sorting of comet chemicals makes 3I more like normal, Solar System comets, which start with their hypervolatiles in the outer reaches (as one would expect) before the water content can warm up enough.
Eubanks et al. is a bit more convoluted, bit more speculative. Based on the low observations of organics, dust, etc. from 3I, it appears that the comet’s home System was an older, “fresher” star system. This older population of stars, predating our Sun, had less heavy elements like silicon and sulfur that can form complex molecules. Appears. Since we are just now measuring nontrivial compositions at ATLAS, I personally feel it’s premature to reach this far, pedagogically.