Breakthrough Listen Observations Of 3I/ATLAS With The Green Bank Telescope at 1-12 GHz

3I/ATLAS (also designated C/2025 N1 (ATLAS) and, formerly, A11pl3Z) is the third interstellar object (ISO), following 1I/‘Oumuamua and 2I/Borisov, to be discovered during a passage through the Solar System. The Asteroid Terrestrial-impact Last Alert System (ATLAS) reported its discovery on 2025 July 1 (S. Deen et al. 2025).

Unlike 1I/‘Oumuamua, 3I/ATLAS exhibits mostly typical cometary characteristics (S. Deen et al. 2025), including a coma and an unelongated nucleus. There is currently no evidence to suggest that ISOs are anything other than natural astrophysical objects. However, given the small number of such objects known (only three to date), and the plausibility of interstellar probes as a technosignature (e.g, R. A. Freitas & F. Valdes 1985), thorough study is warranted (see J. R. A. Davenport et al. 2025).

Putative nonanthropogenic interstellar probes are likely to communicate via narrowband radio signals for transmission efficiency and for the low extinction of such signals across interstellar space; all of humanity’s spacecraft, including the now-interstellar craft Voyager 1 and Voyager 2, communicate via such signals.

The Breakthrough Listen (BL) program observed 3I/ATLAS using the 100-m Robert C. Byrd Green Bank Telescope (GBT) on UT 2025 December 18, ∼1 day before the ISO’s closest approach to Earth. Similar technosignature searches have recently been undertaken by S. Z. Sheikh et al. (2025) and D. J. Pisano et al. (2025) over different frequency ranges and with different sensitivities. Like those searches, we find no credible detections of narrowband radio technosignatures originating from 3I/ATLAS.

Ben Jacobson-Bell, Steve Croft, Ellie White, Andrew P. V. Siemion, Matthew Lebofsky, David H. E. MacMahon

Comments: 3 pages, 1 figure, submitted to RNAAS
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2512.19763 [astro-ph.IM] (or arXiv:2512.19763v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2512.19763
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Submission history
From: Ben Jacobson-Bell
[v1] Sat, 20 Dec 2025 17:52:30 UTC (237 KB)
https://arxiv.org/abs/2512.19763

Astrobiology, Astrochemistry,