Interstellar comet 3I/ATLAS is not an alien spacecraft, astronomers confirm. “In the end, there were no surprises.”

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Space fans hoping that the intruder from beyond the solar system known as Comet 3I/ATLAS is actually an alien spacecraft may be disappointed by new research that could close the book on that speculation once and for all.

Astronomers have used Green Bank Telescopeemployed in Breakthrough Listen astronomy project to hunt for extraterrestrial signals 3I/ATLAS for measurable signs of technology from extraterrestrial civilizations or “technosignatures.”

Although this hunt came up empty, the fact that 3I/ATLAS is only the third known object found in the Solar System after entering from interstellar space (the others being 1I/’Oumuamuaseen in 2017 and 2I/Borisovdetected in 2019) means it is still an object of great fascination, albeit a natural one.

“We would all have been excited to find technical signatures coming from 3I/ATLAS, but they’re just not there,” lead researcher Benjamin Jacobson-Bell of the University of California, Berkeley, told Space.com. “Finding no signal was the result we expected, given the significant evidence that 3I/ATLAS is a comet with only natural features.

“The evidence was against 3I/ATLAS being such a probe, but we would be remiss not to check.”

Jacobson-Bell explained that scientists have even discussed doing this exact type of exploration using probes of their own. An example of this is The innovative Starshot initiativea concept that aims to launch thousands of extremely light probes to Alpha Centaurithe closest star system to our sun.

“There are compelling reasons to believe that a space-faring species would send probes to other star systems as a way to learn more about their stellar neighborhood,” added Jacobson-Bell.

It is broadcast on radio 3I/ATLAS

The team behind this research theorized that if we find them, the brightest extraterrestrial technosignatures are likely to be narrowband radio signals because they require relatively little energy to produce and travel well over long distances.

“Breakthrough Listen searches for life beyond Earth in a variety of ways. The Green Bank Telescope is a 100-meter-wide radio antenna located in an area federally regulated to be free of most radio interference,” Jacobson-Bell said. “Its sensitivity allows us to verify the absence of transmitters down to 0.1 watts, the strongest evidence against the technology of any 3I/ATLAS observation to date.”

For comparison, modern cell phones typically emit radio waves at the level of about 1 watt.

“This means that if there were transmitters on 3I/ATLAS up to ten times weaker than a cell phone, we would have found them,” Jacobson-Bell continued.

“Humans produce a lot of narrowband radio signals, including for communication with our own spacecraft,” Jacobson-Bell said. “However, by modeling our search strategy on human technological output, we end up detecting a lot of man-made signals! So we run any detections through filters to distinguish likely man-made interference from possible extraterrestrial signals.”

The Green Bank telescope covers a very wide range of radio frequencies, meaning it’s unlikely the team missed signals just because they were looking in the wrong part of the the electromagnetic spectrum.

“We found nine ‘events,’ which is our term for signals that pass certain filters in our search strategy, but upon closer inspection, we could easily assign them to all nine known radio transmitters here on Earth,” Jacobson-Bell said. It’s very common to find and then throw false alarms like this.

“Previous work has shown that 3I/ATLAS looks like a comet and behaves like a comet, and our observations show that, like a comet, 3I/ATLAS is not a source of technological signals. In the end, there were no surprises.”

As Jacobson-Bell pointed out, this can be slightly disappointing, but it doesn’t mean that 3I/ATLAS isn’t still extremely scientifically significant.

“There is considerable excitement surrounding 3I/ATLAS as it is only the third discovery of an interstellar object in our solar system,” he continued. “Sending spacecraft to other star systems could be very informative, so it’s tempting to imagine that some interstellar objects could be intentional probes.”

Jacobson-Bell believes that discoveries of interstellar objects are likely to become much more common with the recent completion of Vera C. Rubin Observatory begins its 10-year Legacy Survey of Space and Time (LSST).

“While each individual interstellar object is currently an anomaly, future surveys will gather such a population of interstellar objects that we will begin to be able to tell which are typical and which are actually anomalous,” he said. “Some of these objects will merit further observation – could their anomalies be due to technology?”

This new research and its findings on 3I/ATLAS thus pave the way to answering this question.

“We hope that our search will help dispel the idea that this object is artificial, but we also hope that public interest in interstellar objects remains strong – they are very interesting, whether they are spacecraft or comets, and it is quite possible that one day one of them will indeed transmit technological signals,” concluded Jacobson-Bell. “If we don’t look, we’ll never know.”

The team’s research is available as a peer-reviewed paper on the repository website arXiv.