The first radio signal from comet 3I/Atlas ended the debate about its nature

There is more evidence To support the natural origin of comet 3I/Atlas emerged. After weeks of conspiracy theories, social media debates and speculation from popular podcasters like Joe Rogan, this interstellar object is still a comet. The latest confirmation comes from an observatory in South Africa that detected the first radio signal from 3I/Atlas.

But how? Radio signal? That should confirm that the object is technical in nature, shouldn’t it? The thing is, it’s not a radio signal like a transmission emitted by a spacecraft. This is a radio frequency pattern detected by MeerKAT, a radio telescope consisting of 64 antennas – each 13.5 meters in diameter – operated by the South African Radio Astronomy Observatory. And what did he recognize? According to the researchers, “OH absorption was detected in the 1665 MHz and 1667 MHz lines.”

What MeerKAT specifically detected were radio absorption lines by hydroxyl radicals, namely OH molecules, a pattern consistent with typical comet activity. The lines appear as absorption because 3I/Atlas was very close to the Sun and the observed geometry favors absorption over emission. It’s a phenomenon described a few days ago on WIRED when discussing non-gravitational acceleration: when comets reach their closest point to the Sun, they blast ice into space and receive more radiation. This also causes them to change course.

The hydroxyl radical (OH) can absorb or emit radiation at certain frequencies (such as the 1665 and 1667 MHz lines) due to changes 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 regions of the universe because it can “glow” intensely at radio frequencies under certain conditions.

Is there still hope for something more than a comet?

The discovery was made possible on October 24, five days before 3I/Atlas reached its closest point to the Sun. MeerKAT had previously tried to detect radio signals on September 20 and 28, but was unsuccessful. “Five weeks ago, I encouraged radio observatories like MeerKAT to look for radio emissions from 3I/ATLAS, noting that the direction of arrival of 3I/ATLAS coincided with the direction of arrival of the Wow signal at 9 degrees! In response, I was assured that 3I/ATLAS would be monitored by radio observatories like MeerKAT.

Loeb acknowledged that “no 3I/ATLAS radio detections other than the OH absorption signal have been reported so far.” Of course, continued monitoring of the object needs to be done to determine whether OH production is constant or intermittent, along with factors such as the extent and structure of the tail, to draw firmer conclusions about its nature.

Loeb has been one of the staunchest defenders of the hypothesis that 3I/Atlas has a technological origin. (And he’s already invited Kim Kardashian to join his research team.) MeerKAT’s findings haven’t dampened his motivation to explore the comet’s nature. “3I/ATLAS is expected to pass within 53 million km of Jupiter on March 16, 2026. At that time, the Juno spacecraft will use its dipole antenna to search for a radio signal from 3I/ATLAS at frequencies as low as 50 Hz to 40 MHz,” he wrote.

Is the MeerKAT detection enough to end the conspiracy theories about 3I/Atlas? Probably not, and at least the debate has increased the public’s awareness and interest in astrophysics. In the meantime, you can view the 3I/Atlas comet track here. And don’t forget to mark December 19th on your calendar—that’s when the interstellar visitor will make its closest approach to Earth.

This story for the first time in wired Spanish en and translated from Spanish.