3I/ATLAS is not an alien spacecraft: SETI technosignature search comes up empty
Science

3I/ATLAS is not an alien spacecraft: SETI technosignature search comes up empty

Tianjiangshuo·

3I/ATLAS is not an alien spacecraft: SETI technosignature search comes up empty

Summary: On June 4, 2026, a SETI team published results from Allen Telescope Array observations of interstellar comet 3I/ATLAS. No narrowband radio signals matching an artificial transmitter were detected across multiple bands, reinforcing the natural-origin interpretation. The technosignature hunt follows May observations by Tianwen-1 from Mars orbit and the late-May archival discovery at the Vera C. Rubin Observatory.

Allen Telescope Array at the Hat Creek Radio Observatory in Northern California (Wikimedia Commons, brewbooks, CC BY-SA 2.0)

3I/ATLAS, discovered in July 2025, is the third known interstellar object, following 1I/ʻOumuamua (2017) and 2I/Borisov (2019). With a hyperbolic orbit and eccentricity of about 6.14, it likely originated outside the Solar System billions of years ago. Its larger size and active dust coma have fueled speculation about an artificial origin since discovery. The SETI Institute team used the Allen Telescope Array at the Hat Creek Radio Observatory in Northern California to scan multiple narrowband radio frequencies commonly associated with artificial transmitters, finding no persistent, periodic, or band-matched signals above the natural background.

3I/ATLAS made a close pass by Mars at about 0.194 astronomical units in October 2025, offering a unique vantage point for spacecraft in Mars orbit. China's Tianwen-1 orbiter used its High-resolution Imaging Camera (HIRIC) to image 3I/ATLAS multiple times during the flyby — the first Mars-orbit observations of an interstellar object's dust activity, published in The Astrophysical Journal Letters (ApJL) in May. Separately, astronomers reviewing archival data from the Vera C. Rubin Observatory found that 3I/ATLAS had been captured on images as early as June 21 to July 2, 2025 — more than a week before its official discovery.

From archival precovery to Mars-orbit dust imaging to dedicated technosignature searches, the 3I/ATLAS observational campaign has unfolded in three distinct stages this year. While a null result from SETI does not entirely foreclose "alien spacecraft" speculation, it adds another independent line of evidence supporting the natural-origin interpretation.

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