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.