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This content will become publicly available on September 11, 2026

Title: Precovery Observations of 3I/ATLAS from TESS Suggest Possible Distant Activity
Abstract 3I/ATLAS is the third macroscopic interstellar object detected traversing the solar system. Since its initial discovery on UT 2025 July 1, hundreds of hours on a range of observational facilities have been dedicated to measuring 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 2025 May 7 to 2025 June 2. We use the shift-stack method to create deepstack images to recover the object. These composite images reveal that 3I/ATLAS has an average TESS magnitude ofTmag = 20.83 ± 0.05, 19.28 ± 0.05 and an absolute visual magnitude ofHV = 13.72 ± 0.35;12.52 ± 0.35, the latter being consistent with magnitudes reported in 2025 July. When coupled with recent Hubble Space Telescope images deriving a nucleus size ofR< 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.  more » « less
Award ID(s):
2303553
PAR ID:
10646047
Author(s) / Creator(s):
; ;
Publisher / Repository:
AAS Journals
Date Published:
Journal Name:
The Astrophysical Journal Letters
Volume:
991
Issue:
1
ISSN:
2041-8205
Page Range / eLocation ID:
L2
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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