2025/07/29 by Adina D. Feinstein, John W. Noonan, Feinstein, Adina D. +3 · 5 voices · 9 citations
Physics and Astronomy · #astro-ph.EP #astro-ph.GA
paper · pdf · doi:10.48550/arxiv.2507.21967
3I/ATLAS is the third macroscopic interstellar object detected traversing the Solar System. Since its initial discovery on UT 01 July 2025, hundreds of hours on a range of observational facilities have been dedicated to measure the physical properties of this object. These observations have provided astrometry to refine the orbital solution, photometry to measure the color, a rotation period and secular light curve, and spectroscopy to characterize the composition of the coma. Here, we report precovery photometry of 3I/ATLAS as observed with NASA's Transiting Exoplanet Survey Satellite (TESS). 3I/ATLAS was observed nearly continuously by TESS from UT 07 May 2025 to 02 June 2025. We use the shift-stack method to create deep stack images to recover the object. These composite images reveal that 3I/ATLAS has an average TESS magnitude of T_\textrmmag = 20.83 ± 0.05, 19.28 ± 0.05 and an absolute visual magnitude of HV = 13.72 ± 0.35; 12.52 ± 0.35, the latter being consistent with magnitudes reported in July 2025. When coupled with recent HST images deriving a nucleus size of R<2.8 km (H>15.4), our measurements suggest that 3I/ATLAS may have been active out at ∼ 6 au. Additionally, we extract a ∼ 20 day light curve and find no statistically significant evidence of a nucleus rotation period. Nevertheless, the data presented here are some of the earliest precovery images of 3I/ATLAS and may be used in conjunction with future observations to constrain the properties of our third interstellar interloper.