The SETI Institute’s Allen Telescope Array is a 42-element radio interferometer located at the Hat Creek Radio Astronomy Observatory in Hat Creek, California. Astronomers have been searching for artificial radio transmissions from the interstellar object 3I/ATLAS but have only detected man-made interference.
This image from the Subaru Telescope features the interstellar comet 3I/ATLAS and is provided by the National Astronomical Observatory of Japan.
3I/ATLAS is the third confirmed object to enter our solar system from another star system, following 1I/’Oumuamua and 2I/Borisov.
While evidence strongly suggests that 3I/ATLAS is a natural object, interstellar visitors also serve as intriguing technosignature targets, as artificial objects could indicate detectable extraterrestrial technology and potentially provide the first proof of extraterrestrial life.
“On July 1, 2025, 3I/ATLAS, initially classified as C/2025 N1 (ATLAS), was discovered by the Asteroid-Earth Impact Final Alert System (ATLAS) in Rio Hurtado, Chile,” stated Dr. Sofia Sheikh from the SETI Institute and her colleagues.
“Numerous telescopes globally are tracking the orbit of 3I/ATLAS, revealing significant cometary activity through continued monitoring.”
“If this object is indeed a comet, as anticipated based on initial characterizations, it should contain volatiles and develop a prominent tail after passing perihelion.”
“Initial observations indicated that the object appeared red and developed a coma due to its luminescence as it neared the Sun.”
“Despite reaching perihelion on October 29, 2025, observations from Earth were notably affected from September to early November due to its proximity to the Sun.”
“There remains much to learn about this interstellar visitor, so the ability to observe it during its approach represents a significant scientific advantage.”
5.29 Output waterfall plot from a 3I/ATLAS observation, showing no signals exceeding the SNR ratio threshold. This signal exhibited unblanked frequencies, an acceptable drift rate, and appears to be truly narrowband. Nevertheless, the SNR of the signal is similar both on-beam and off-beam, suggesting local interference sources within the provided quota for fixed satellite services (Earth-to-space). Image credit: Sheikh et al., doi: 10.3847/1538-3881/ae6651.
During this observation campaign, astronomers spent over seven hours analyzing 3I/ATLAS using the Allen Telescope Array, targeting frequencies from 1 to 9 GHz.
Approximately 74 million narrowband signals were identified. After excluding interference and filtering out signals matching the object’s motion, around 200 signals remained for further analysis.
This reinforces the notion that the observed signals primarily derive from Earth’s surface technology or its orbiting satellites.
Despite no technosignatures being found, this investigation established new constraints indicating that 3I/ATLAS is a natural object.
This observation sets an upper limit on the radio transmitters’ power on or near 3I/ATLAS, filtering out signals stronger than around 10 to 110 watts (similar to household appliances) across the detected frequencies.
“The findings from 3I/ATLAS demonstrate the feasibility of detecting signals with current technology,” remarked Dr. Valeria García López, an astronomer at Furman University and director of the Breakthrough Listening Initiative.
“This underlines the importance of searching for technosignatures, even in objects where we might not anticipate any signals.”
The team’s research will be published in Astronomy Magazine.
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Sophia Z. Sheikh et al. 2026. “Retrieval of Radiotechnical Signatures from Interstellar Object 3I/ATLAS Using the Allen Telescope Array.” A.J. 172, 1; doi: 10.3847/1538-3881/ae6651
Source: www.sci.news
