Pre-discovery TESS Observations of Interstellar Object 3I/ATLAS
Jorge Martinez-Palomera (1,2), Amy Tuson (1,2), Christina Hedges (1,2), Jessie Dotson (3), Thomas Barclay (2), and Brian Powell (2) ((1) University of Maryland, Baltimore County, (2) NASA Goddard Space Flight Center, (3) NASA Ames Research Center)

TL;DR
This paper reports pre-discovery TESS observations of interstellar object 3I/ATLAS, revealing its brightness increase and faint activity as it approaches the inner Solar System, demonstrating TESS's utility for Solar System studies.
Contribution
First detection of 3I/ATLAS in TESS data prior to its discovery, showcasing TESS's potential for interstellar object observation and long-term activity analysis.
Findings
3I/ATLAS was detected in TESS data 55 days before discovery.
Brightness increased from magnitude 20.9 to 19.57 as it approached the Sun.
Faint activity consistent with other observations was observed.
Abstract
3I/ATLAS, also known as C2025 N1 (ATLAS), is the third known macroscopic interstellar object to pass through our Solar System. We report serendipitous Transiting Exoplanet Survey Satellite (TESS) observations of 3I/ATLAS taken between 2025-05-07 and 2025-06-02, 55 days prior to the discovery date (2025-07-01). We retrieve the TESS pixel data, perform a robust background correction and use a data-driven approach to compute the objects position on the TESS detectors. We find a consistent offset between the targets observed and predicted positions which is dominated by uncertainty in the TESS World Coordinate System (WCS) rather than ephemeris errors. 3I/ATLAS is too faint to be detected in the individual 200 second TESS integrations, so we stack images to improve detectability. We perform aperture and Pixel Response Function (PRF) photometry on the stacked images to create two light…
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Taxonomy
TopicsAstronomy and Astrophysical Research · Astrophysics and Star Formation Studies · Gamma-ray bursts and supernovae
