Blogworthy two ways:
Astrophysics > Earth and Planetary Astrophysics arxiv.org/abs/2507.13409
[Submitted on 17 Jul 2025]
Chandler, C. O. Bernardinelli, P. H. Jurić, M. et al, NSF-DOE Vera C. Rubin Observatory Observations of Interstellar Comet 3I/ATLAS (C/2025 N1)
The Rubin Observatory is so good at sky surveying, it precovered object 3I/ATLAS. Without even trying, the small body was caught in images dating back (before official discovery, July 1) from June 21. It just hadn’t been recognized; once word got out, program staff combed the saved shots from that area of sky. Sure enough, Rubin had taken images there, and got the comet.
And what do we know from that precovery? First off, having those extra days extends the observing arc. With several more days of tracking, we can solve for 3I’s orbit that much better. Second, activity (a faint emission, causing a coma) was already detectable back then- when the object was near Jupiter’s orbit and nowhere near the Sun. Tracking the onset of activity, and its progression, tells us of the volatiles present in 3I (including, apparently, supervolatiles, which can emit despite the cooler temperatures there).
The fact that Rubin caught 3I/ATLAS without even trying bodes well for future small-body search.