English

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

Earth and Planetary Astrophysics 2025-08-27 v3 Astrophysics of Galaxies

Abstract

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 Tmag=20.83±0.05,19.28±0.05T_\textrm{mag} = 20.83 \pm 0.05, 19.28 \pm 0.05 and an absolute visual magnitude of HV=13.72±0.35;12.52±0.35H_V = 13.72 \pm 0.35; 12.52 \pm 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\sim 6 au. Additionally, we extract a 20\sim 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.

Keywords

Cite

@article{arxiv.2507.21967,
  title  = {Precovery Observations of 3I/ATLAS from TESS Suggests Possible Distant Activity},
  author = {Adina D. Feinstein and John W. Noonan and Darryl Z. Seligman},
  journal= {arXiv preprint arXiv:2507.21967},
  year   = {2025}
}

Comments

16 pages, 12 figures. Accepted at AAS Journals (August 19, 2025). Data behind the figures can be found here: https://github.com/afeinstein20/atlas-tess and https://zenodo.org/records/16943786