There is more evidence appeared to confirm the natural origin of comet 3I/Atlas. After weeks of conspiracy theories, social media debates, and speculation on popular podcasts like Joe Rogan’s, this interstellar object is still a comet. The latest confirmation comes from an observatory in South Africa, which recorded the first radio signal from 3I/Atlas.
But how? Radio signal? This would have to confirm that the object is technological in nature, right? The thing is, it’s not a radio signal like a transmission from a spacecraft. Instead, it is a radio frequency pattern detected by MeerKAT, a radio telescope made up of 64 antennas – each 13.5 meters in diameter – operated by the South African Radio Astronomy Observatory. And what did he detect? “OH absorption detected on the 1665 MHz and 1667 MHz lines” According to researchers.
MeerKAT specifically detected radio absorption lines of hydroxyl radicals, or OH molecules, which would be consistent with typical comet activity. The lines appear to be absorption because 3I/Atlas was very close to the Sun and the observing geometry favors absorption over emission. This is a phenomenon explained at WIRED a few days ago when the non-gravitational acceleration controversy 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 change their trajectory.
The hydroxyl radical (OH) can absorb or emit radiation at specific frequencies (such as the 1665 and 1667 MHz lines) due to changes in energy levels. These OH spectral lines have been detected in nebulae, comets and star-forming regions. OH helps astronomers map areas of the universe made of stars and water because it can “shine” brightly at radio frequencies under certain conditions.
Is there still hope that this is more than a comet?
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, but was unsuccessful. “Five weeks ago, I encouraged radio observatories like MeerKAT to search for radio emissions from 3I/ATLAS, given that 3I/ATLAS’s arrival direction aligned with 3I/ATLAS’s arrival direction to within 9 degrees Wow! Signal detected in 1977 at a frequency of 1.4204556 gigahertz,” wrote astrophysicist Avi Loeb on Medium post. “In response, I was assured that 3I/ATLAS would be monitored by radio observatories such as MeerKAT.”
Loeb admitted that “no radio detection of 3I/ATLAS other than the OH absorption signal has been reported to date.” Of course, it would be necessary to continuously monitor the facility to determine whether OH production is continuous or intermittent, and to take into account factors such as the extent and structure of the tail to draw more resilient conclusions about its nature.
Loeb was one of the most vocal supporters of the hypothesis that 3I/Atlas had a technological origin. (And he he has already invited Kim Kardashian join his research team.). MeerKAT’s discoveries did not dampen his zeal to study the nature of the comet. “3I/ATLAS is expected to fly within 53 million kilometers of Jupiter on March 16, 2026. During this time, Juno will use its dipole antenna to search for a radio signal from 3I/ATLAS at low frequencies in the range of 50 hertz to 40 megahertz,” he wrote.
Will the discovery of MeerKAT be enough to put an end to 3I/Atlas conspiracy theories? Probably not, or at least the debates have increased public awareness and interest in astrophysics. In the meantime, you can follow the trajectory of Comet 3I/Atlas live here. And don’t forget to mark December 19 on your calendar – that’s when the interstellar visitor will be closest to Earth.
This story first appeared WIRED in Spanish and was translated from Spanish.