Mustn’t let our interstellar guest slip away unnoticed:
Astrophysics > Earth and Planetary Astrophysics arxiv.org/abs/2602.21586
Hartman, J. D. Bakos, G. Á. Jordan, A. et al. HATPI Pre-Perihelion Time-series Photometry of the Interstellar Comet 3I/ATLAS
[Submitted on 25 Feb 2026]
Standard Disclaimer: The arXiv preprint site is, well… a preprint site. All papers on it are, at best, prior drafts of papers about to be officially and pedagogically released (in peer-reviewed science journals). At worst, a few papers posted on arXiv are unfit to be seen anywhere else.
Okay, preliminaries aside. The HATPI telescope array caught interstellar object 3I/ATLAS without even trying. The array consists of multiple small (really- centimeters aperture) “telescopes” to cover the sky. Officially, the quarry is sky transients: variable stars, supernovae, gamma-ray bursts and other such bumps in the night, and only occasionally a bright asteroid. And yet, ATLAS qualifies. At first, the comet was a bit dim for HATPI, and researchers had to postprocess the images (already knowing what to look for) to bring it out. Eventually, ATLAS neared the Sun, warmed, and brightened, by releasing more gases and dust. It has now passed perihelion, is receding into the outer Solar System, and cooling. All the way, HATPI has (by pure chance) logged its brightness. That history of brightening and dimming (its “lightcurve”) tells us of its ice/gas makeup. Hartman et al. tell us of the HATPI lightcurve, which by the way is not a perfect match to the results of other groups. Science moves forward when we resolve these differences.