In the summer of 2025, the Asteroid Terrestrial-impact Last Alert System (ATLAS), a survey telescope in Chile, discovered 3I/ATLAS, only the third known interstellar object to pass through our solar system. Its uncertain origin and trajectory, which brought it through the region between the Sun and Mars, gave scientists a rare but brief opportunity to study material from beyond the solar system.
Why 3I/ATLAS attracted speculation
Most astronomers focused on 3I/ATLAS’s physical and chemical properties. However, some scientists raised the possibility that it could display evidence of advanced alien technology, also known as a technosignature. Under that hypothesis, 3I/ATLAS would be the most prominent extraterrestrial technosignature ever observed.
Compared with ‘Oumuamua, the first known interstellar object, which was several hundred meters long—about 1,000 feet—3I/ATLAS had an upper size estimate in the kilometer, or mile, range. Some observers also noted that its path was roughly aligned with the plane in which the solar system’s planets orbit. At first, it did not show the glowing tail expected from a natural object passing through the solar system.
The eventual scientific consensus was that 3I/ATLAS was not an alien probe or mothership sent to study or destroy Earth. Scientists have no reason to expect interstellar objects to have a particular size, and three recorded objects are not enough to support meaningful statistical comparisons. In addition, ATLAS’s field of view is aligned with the planetary orbits, so it is not surprising that the system discovered an object moving through that region.
Further observations eventually revealed the typical glowing tail associated with a comet. The most likely explanation is therefore that 3I/ATLAS is a piece of space debris—either material that was originally floating freely or debris from another star system—that was sent toward our solar system by an unknown event millions of years ago.
Searching for artificial radio signals
Even though 3I/ATLAS is probably natural, it provides a useful case study for how scientists might search for technosignatures from an actual alien object in the future. A team of Chinese scientists recently used the Five-hundred-meter Aperture Spherical Telescope (FAST) to look for unusual radio signals from the object.
Other radio telescopes had already observed 3I/ATLAS, but FAST is one of the world’s most powerful radio telescopes. The researchers therefore applied several methods to determine whether any detected signal could have been produced by technology rather than natural processes.
The team analyzed data collected while FAST was pointed at 3I/ATLAS in 2025. The telescope recorded radio waves between 1.05 and 1.45 gigahertz at intervals of about 49 microseconds. The researchers divided the measurements into time segments and searched for unusual signals or recurring patterns over periods ranging from 0.7 seconds to 1,000 seconds.
According to the researchers, FAST’s sensitivity and data-processing methods allow it to detect artificial radio signals within the target frequency range from devices transmitting at 0.15 watts or more. The analysis found no evidence of an artificial signal in the FAST data, further supporting the widely accepted conclusion that 3I/ATLAS is rare space debris rather than the vanguard of an alien fleet.
Lessons for future technosignature searches
The research team concluded that the tests demonstrated FAST’s ability to search for technosignatures in the universe. However, the scientists recommended that future observations run for longer periods and examine a broader range of signal durations, including timescales down to microseconds.
3I/ATLAS will eventually leave the solar system. Millions of years from now, perhaps an alien scientific team could use the object—or another interstellar visitor—to test its own ability to detect technosignatures.
Source: sciworthy.com
