Search for Alien Technology on Interstellar Comet 3I/ATLAS Yields No Detection
Radio astronomers using the Allen Telescope Array found no technosignatures — artificial radio signals — from interstellar comet 3I/ATLAS, while separate optical spectroscopy studies have detailed its complex natural coma chemistry. 3I/ATLAS, discovered in July 2025, is only the third known interstellar object to enter our solar system, following 'Oumuamua and Borisov. The null SETI result, published in The Astronomical Journal, still provides valuable methodology practice and places firm upper limits on any radio transmitter power near the comet, while the spectroscopic findings reinforce its identity as a natural icy body from another solar system.
When interstellar comet 3I/ATLAS was first detected on July 1, 2025, by the ATLAS survey telescope in Chile, its high speed of roughly 137,000 miles per hour and interstellar origin prompted both planetary scientists and SETI researchers to study it closely. A team led by Sofia Sheikh of the SETI Institute used the Allen Telescope Array in Northern California to collect more than seven hours of radio observations, searching for narrowband signals that cannot be produced by natural phenomena. Starting from nearly 74 million candidate signals, the team filtered out human interference and satellite artifacts, ultimately reducing the pool to about 200 signals — all of which were explained as terrestrial or satellite in origin. The study places upper limits on any radio transmitter associated with 3I/ATLAS at roughly 10–110 watts, approximately the power of a household appliance. Separately, optical spectroscopy conducted between December 2025 and January 2026 — published as a preprint on arXiv and accepted in The Astrophysical Journal Letters — revealed a chemically rich coma containing CN, C₂, C₃, CH, and gaseous metals including iron and nickel, with outgassing patterns showing a pronounced perihelion asymmetry consistent with subsurface activation or compositional heterogeneity. Telescope imagery confirms the comet's classic appearance, with a bright nucleus surrounded by a diffuse coma. Together, the radio and optical studies strongly reinforce the conclusion that 3I/ATLAS is a natural comet, while also advancing methodologies for identifying any future interstellar object that might genuinely be artificial.
Limitations & open questions
The spectroscopic preprint (Source 3) notes a significant residual in the [O I] λ6300 emission line that cannot be fully explained by known oxygen-bearing parent molecules, and acknowledges systematic uncertainties in photodissociation yields — an open question about 3I/ATLAS's full chemical inventory that the news coverage does not address.
How coverage differed
Scientific American and Space.com covered the SETI null-result story with nearly identical framing, both emphasizing the value of the negative finding for future searches; Space.com provided more technical detail on signal filtering methodology, while Scientific American focused more on the broader scientific philosophy of studying natural interstellar objects.
What different sources said
- arXiv astro-phCenter
Post-perihelion Coma Composition of the Interstellar Comet 3I/ATLAS from Optical Spectroscopy
- Space.comCenter
Interstellar comet 3I/ATLAS is not an alien spacecraft: SETI hunt for 'technosignatures' comes up empty
- Scientific AmericanCenter
Search for alien technology on interstellar Comet 3I/ATLAS comes up empty
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