The ATLAS papers haven’t stopped- plenty are rushing to get observations in before the comet goes behind the Sun as seen from Earth next month:
Astrophysics > Earth and Planetary Astrophysics arxiv.org/abs/2509.07678
[Submitted on 9 Sep 2025]
Pérez-Couto, X. Torres, S. Villaver, E. et al. 3I/ATLAS: In Search of the Witnesses to Its Voyage
arxiv.org/abs/2509.08792
[Submitted on 10 Sep 2025]
Ye, Q. Kelley, M. S. P. Hsieh, H. H. et al. Prediscovery Activity of New Interstellar Object 3I/ATLAS: A Dynamically-Old Comet?
In both cases, a long observing arc (a few months’ span) is enabling. In the case of Pérez-Couto et al., a precise orbit determination can be used for a precise ‘pre-determination’- where did ATLAS come from, based on tracing its path back through interstellar space? The authors find that few stars match our current trajectory numbers; there isn’t really a ‘smoking gun’ solution for ATLAS’ home system, or even a flyby to deflect that trajectory. Interestingly enough, the authors find that a home system in the Milky Way’s thin disc is more likely, contradicting prior papers.
In the case of Ye et al., a precise orbit determination allowed them to go back and find ATLAS in archived images- what we call “precovery”. Not a dim object, ATLAS could be found (now that we know what to look for) in archived ZTF (Zwicky Transient Facility) images going back a year ago! Seeing what the year-ago ATLAS looked like, we can now constrain what the activity level and warm-up phenomena were like. We can now constrain the supervolatile activity (loss of volatiles that boil off before water does) while 3I was in the outer Solar System, and colder.