In the summer of 2025, the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope in Chile found the third deep-space object known to pass through our solar system. Since it was the third documented interstellar object and was discovered by the ATLAS system, scientists designated it 3I/ATLAS. With uncertain origins and a trajectory that would bring it close enough to Earth to pass between the Sun and Mars, 3I/ATLAS offered a rare but brief opportunity for researchers to study what lies beyond the solar system.
While most astronomers’ interest in 3I/ATLAS focused on its physical and chemical features, some scientists raised concerns that it could represent evidence of advanced alien technology, also known as a technosignature. Under this hypothesis, 3I/ATLAS would be the most prominent extraterrestrial technosignature ever observed. Compared to the other interstellar objects, like ‘Oumuamua, that were a few hundred meters or around a thousand feet long, high-end estimates for the length of 3I/ATLAS are in the kilometers or miles range. It’s also moving along the approximate plane in which the solar system’s planets orbit, a fact some thought was unlikely to be a coincidence. And it didn’t exhibit the glowing tail expected from natural objects flying through the solar system, at least not at first.
Ultimately, the consensus was that 3I/ATLAS is not an alien probe or mothership sent to study or destroy Earth. There’s no reason scientists should expect interstellar objects to be any particular size, since 3I/ATLAS is only the third of its kind on record, and 3 items are insufficient for statistical comparison. In addition, ATLAS’s view aligns with the orbits of the planets in the solar system, so it isn’t surprising that it found an object within that plane. And with more observations, 3I/ATLAS eventually showed signs of a typical glowing tail. Therefore, the most likely scenario is that it’s some kind of space debris, either originally free-floating or from another star system, that was sent flying towards the solar system by an unknown event millions of years ago.
Regardless, 3I/ATLAS still presents a case study for how scientists might one day spot an actual alien technosignature flying through the solar system. A team of scientists in China recently tested whether they could detect unusual radio signals coming from it using the Five-hundred-meter Aperture Spherical Telescope (FAST). While other radio telescopes had already observed 3I/ATLAS, FAST is one of the most powerful, so these researchers tried different methods to see whether they would observe any potentially artificial signals.
The team used data that FAST collected when it was pointed at 3I/ATLAS in 2025. At that time, the telescope measured radio waves from 3I/ATLAS in the 1.05 to 1.45 gigahertz range at intervals of about 49 microseconds. They divided the radio wave measurements into time segments to see whether any unusual signals or patterns recurred, and they repeated this for time periods from 0.7 seconds to 1,000 seconds.
The researchers claimed that, given FAST’s sensitivity and how they processed its data, they could detect any artificial radio signal within their target frequency range from devices using 0.15 watts or more. They found no evidence of artificial signals in the FAST data, further supporting the widely accepted claim that 3I/ATLAS is an unusual piece of space debris, not the vanguard of an alien armada.
The team concluded that their tests showed FAST could detect technosignatures in space. However, they recommended that future scientists run longer searches and extend the range of signal periods down to the microsecond scale. Eventually, 3I/ATLAS’s trajectory will take it out of the solar system, and perhaps, in a few million years, teams of alien scientists could use it to test their own capacity to find technosignatures.
