When Comet 3I/ATLAS entered our solar system last year—only the third known interstellar object to do so—astronomers took notice. And so did scientists searching for extraterrestrial intelligence, who were curious whether this particular interloper may have been linked to aliens.
When astronomers first discovered 3I/ATLAS in July 2025, the icy body was traveling at an impressive speed of about 137,000 miles per hour. Researchers later discovered that it is “bursting with methanol” and its coma—the vapor envelope that forms as the icy object nears the sun—is full of frozen carbon dioxide. Both observations provide astronomers with clues about the comet’s cosmic origin. All signs suggested the interstellar object was natural, but some astronomers took the opportunity to look for so-called "technosignatures," particularly radio signals that could be produced by an artificial thing.
“Eventually, our own Voyager spacecraft will be extraterrestrial artifacts in other stellar systems,” said Sofia Sheikh, a research scientist at the SETI Institute, in a statement, referring to the twin interstellar probes that NASA launched in 1977. “Given that, it is important that we understand the natural distribution of interstellar objects so that we will be able to identify any anomalies that could one day be signs of an artificial interstellar object.”
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To help rule out the possibility that 3I/ATLAS contained some kind of alien technology, Sheikh and colleagues tracked the comet with a radio telescope, the Allen Telescope Array (ATA), and looked for narrowband radio signals—“the kind that can only come from technology,” Sheikh says. “After analyzing several hours of data across the full frequency range of the ATA,” Sheikh and the team did not see any signals, or technosignatures, associated with 3I/ATLAS, she says.
Sheikh wasn’t surprised by the results. “All of the evidence that the global scientific community had found before, during, and after our observations indicated that 3I/ATLAS was an icy rock from another solar system—extremely cool from a planetary science perspective, but not in any way a technological artifact,” she says.
That doesn’t mean the study wasn’t valuable. For one, null results—in this case, findings that are not unusual or revelatory—are still useful. And, as Sheikh says, it’s good practice for the next interstellar object.
“By better understanding natural objects like 3I/ATLAS and practicing our methodologies on real-world events, we are better prepared to observe and analyze other interstellar objects, including potentially artificial objects, in the future,” she says.
The new study published on Wednesday in the Astronomical Journal.
