Other evidence has emerged to support the natural origin of comet 3I/Atlas. After several weeks of conspiracy theories, debates on social media 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 which detected the first radio signal from 3I/Atlas.
But how? A radio signal? This should confirm that the object is technological in nature, right? The fact is that it is not a radio signal like a transmission from a spacecraft. Rather, it is a radio frequency pattern detected by MeerKAT, a radio telescope made up 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 radio absorption lines by hydroxyl radicals, i.e. OH molecules, a pattern that would be consistent with typical comet activity. The lines appear as an absorption because 3I/Atlas was very close to the sun and the observation geometry favors absorption over emission. This is the phenomenon explained in WIRED a few days ago, when the controversy over non-gravitational acceleration erupted: when comets reach their closest point to the sun, they sublimate the ice in 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 transitions in its energy levels. These OH spectral lines have been detected in nebulae, comets and star forming regions. OH helps astronomers map the stellar and watery 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, but was unsuccessful. “Five weeks ago, I encouraged radio observatories like MeerKAT to search for radio emissions from 3I/ATLAS given that the direction of arrival of 3I/ATLAS coincided within 9 degrees with the direction of arrival of the Wow! signal detected in 1977 at a frequency of 1.4204556 gigahertz,” astrophysicist Avi Loeb wrote in an article on Medium. “In response, I was assured that 3I/ATLAS would be monitored by radio observatories like MeerKAT.”
Loeb acknowledged that “no radio detections of 3I/ATLAS have been reported so far, other than the OH absorption signal.” Of course, continuous monitoring of the object should be carried out to determine whether OH production is constant or intermittent, as well as factors such as the extent and structure of the tail, in order to reach more robust conclusions about its nature.
Loeb has been one of the strongest advocates of the hypothesis that 3I/Atlas has a technological origin. (And he’s already invited Kim Kardashian to join his research team.). MeerKAT’s discoveries have not dampened its drive to probe the nature of the comet. “On March 16, 2026, 3I/ATLAS is expected to pass within 53 million kilometers of 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 detection of MeerKAT be enough to put an end to the conspiracy theories around 3I/Atlas? Probably not, and at least the debates have increased general public awareness and interest in astrophysics. In the meantime, you can experience 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 was translated from Spanish.
