Precovery Observations of 3I/ATLAS from TESS Suggests Possible Distant Activity

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_mag=19.6±0.1 and an absolute visual magnitude of HV=12.5±0.3, consistent with magnitudes reported in July 2025, suggesting that 3I/ATLAS may have been active out at ∼6.4 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.

Adina D. Feinstein, John W. Noonan, Darryl Z. Seligman

Comments: 10 pages, 7 figures, submitted to AAS Journals. Data behind the figures can be found here:this https URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2507.21967 [astro-ph.EP] (or arXiv:2507.21967v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.21967
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Submission history
From: Adina Feinstein
[v1] Tue, 29 Jul 2025 16:16:07 UTC (3,936 KB)
https://arxiv.org/abs/2507.21967
Astrobiology,