A Search for Coma in TESS Observations of Interstellar Comet 3I/ATLAS

The Transiting Exoplanet Survey Satellite observed the interstellar comet 3I/ATLAS in 2025 May–June. Using this extensive data set, we coadded more than 9000 images, in two groups, to look for extended coma that would unambiguously reveal cometary activity. The radial profiles in both coadded groups are comparable to inactive objects, indicating that no extended coma was detected. However, the brightness of 3I in these observations, in light of results from Hubble Space Telescope observations, suggests that there is coma in the central point-spread function. This means that if activity was sustained for any significant length of time, the dust in the coma must have been ejected at very low velocities (<10 m s −1 ).