Astronomers have detected the first radio signal from interstellar comet 3I/ATLAS as it reaches the midpoint of its journey through the solar system. While some had speculated this could confirm the comet’s alleged alien origins, the discovery instead disproves those claims.
3I/ATLAS is the third confirmed interstellar object (ISO) to pass through our solar neighbourhood. Discovered in early July, it was observed travelling toward the Sun at over 130,000 mph (210,000 km/h). Evidence suggests the comet was ejected from a distant star system up to seven billion years ago, making it one of the oldest known visitors of its kind.
Since its discovery, a small group of scientists—most notably Harvard astrophysicist Avi Loeb—has promoted the unfounded theory that 3I/ATLAS could be an alien spacecraft disguised as a comet. The speculation echoes debates surrounding the earlier interstellar visitor ‘Oumuamua, which Loeb similarly proposed might be an extraterrestrial probe.
Recently, astronomers using South Africa’s MeerKAT radio telescope detected radio emissions from 3I/ATLAS. Proponents of the alien hypothesis expected this might indicate an artificial signal, especially as the detection coincided with the comet’s perihelion on October 29. However, analysis revealed that the emissions were not technological. Instead, they were produced by hydroxyl radicals (OH molecules) in the comet’s coma—molecules formed when sunlight breaks down water vapour. This natural process fully explains the signal, reinforcing 3I/ATLAS’s cometary origin.
The presence of hydroxyl radicals is a hallmark of outgassing, a process in which solar radiation causes frozen water within a comet to vaporise. This phenomenon was vividly observed by NASA in October, when researchers documented intense water jets erupting from 3I/ATLAS, likening the event to a “fire hose.” As the comet neared the Sun, solar radiation further decomposed the released water, generating the radio signature detected by MeerKAT.
In an update posted to his blog—followed by over 100,000 readers—Loeb acknowledged the detection of hydroxyl radicals but stopped short of commenting on whether it confirmed natural cometary activity.
Additional radio signals were observed on October 24, shortly after 3I/ATLAS re-emerged from behind the Sun during perihelion. This solar flyby was accompanied by a brief brightening event and a temporary color shift. Although early reports suggested the comet had lost its tail, subsequent observations disproved that claim.
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3I/ATLAS has displayed several unusual features, including a highly irradiated surface, elevated carbon dioxide levels, and an atypical anti-tail. While these have fuelled online speculation, astronomers agree that all can be explained through natural physical processes, confirming that the comet is not artificial.
Further debunking conspiracy theories, astronomers recently identified an “almost interstellar object” that passed near Earth on November 11. Initially rumoured to be a probe linked to 3I/ATLAS, the object—officially designated C/2025 V1 (Borisov)—was confirmed to be an ordinary solar system comet.
Finally, Loeb’s earlier claims that 3I/ATLAS experienced non-gravitational acceleration due to a possible explosion were contradicted by new data. Observations show no evidence of such events, reaffirming that 3I/ATLAS is a natural interstellar comet, not an alien craft.
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