The First Radio Signal From Comet 3I/Atlas Ends the Debate About Its Nature

More evidence has emerged to support the natural origin of comet 3I/Atlas. After several weeks of conspiracy theories, social media debates, and speculation on popular podcasts such as Joe Rogan’s, this interstellar object is still a comet. The most recent confirmation came from an observatory in South Africa that detected the first radio signal from 3I/Atlas.

But how? A radio signal? That would have to confirm the object is technlogical in nature, wouldn’t it? The thing is, this isn’t a radio signal like a transmission emitted by a spacecraft. It’s instead a radio frequency pattern detected by MeerKAT, a radio telescope composed of 64 antennas—each with a diameter of 13.5 meters—operated by the South African Radio Astronomy Observatory. And what did it detect? “OH absorption was detected on the 1665 MHz and 1667 MHz lines,” according to the researchers.

What MeerKAT specifically detected were lines of radio absorption by hydroxyl radicals, that is, OH molecules, a pattern that would be consistent with typical comet activity. The lines appear as absorption because 3I/Atlas was very close to the sun and the observing geometry favors absorption over emission. This is the phenomenon explained in WIRED a few days ago when the controversy about non-gravitational acceleration arose: When comets reach their closest point to the sun, they sublimate ice into space and receive a greater amount of radiation. This also causes them to alter their trajectory.

The hydroxyl radical (OH) can absorb or emit radiation at specific frequencies (such as the 1665 and 1667 MHz lines) due to transitions in its energy levels. These OH spectral lines have been detected in nebulae, comets, and star-forming regions. OH helps astronomers map the star- and water-born regions of the universe because it can “glow” brightly at radio frequencies under certain conditions.

Is There Still Hope That It’s More Than a Comet?

The detection was possible on October 24, five days before 3I/Atlas reached its closest point to the sun. MeerKAT attempted to detect radio signals earlier, on September 20 and 28, although it was unsuccessful. “Five weeks ago, I encouraged radio observatories like MeerKAT to search for radio emission from 3I/ATLAS given that the arrival direction of 3I/ATLAS coincided to within 9 degrees with the arrival direction of the Wow! Signal detected in 1977 at a frequency of 1.4204556 gigahertz,” astrophysicist Avi Loeb wrote in a Medium post. “In response, I was assured that 3I/ATLAS will be monitored by radio observatories like MeerKAT.”

Loeb acknowledged that “no radio detection of 3I/ATLAS has been reported so far, other than the OH absorption signal.” Of course, continued monitoring of the object would need to be conducted to determine whether the OH production is constant or intermittent, along with factors such as the extent and structure of the tail, to reach more solid conclusions about its nature.

Loeb has been has been among the most vocal advocates the of hypothesis that 3I/Atlas has a technological origin. (And he has already invited Kim Kardashian to join his research team.). The MeerKAT findings have not dampened his drive to probe the comet’s nature. “On March 16, 2026, 3I/ATLAS is expected to pass within 53 million kilometers from Jupiter. At that time, the Juno spacecraft will use its dipole antenna to search for a radio signal from 3I/ATLAS at low frequencies ranging from 50 hertz to 40 megahertz,” he wrote.

Will the MeerKAT detection be enough to put an end to conspiracy theories about 3I/Atlas? Likely not, and at least the debates have heightened the general public’s awareness of and interest in astrophysics. In the meantime, you can live the trajectory of comet 3I/Atlas here. And don’t forget to mark December 19 on the calendar—that’s when the interstellar guest will reach its closest point to Earth.

This story first appeared on WIRED en Español and has been translated from Spanish.