Unexplained radio signals detected from 3I/Atlas near the Sun — what scientists know so far

Another mysterious discovery has been observed about 3I/ATLAS. From the fascinating interstellar object in our solar system, scientists have recently detected radio signals using MeerKAT, a radio telescope at the South African Radio Astronomy Observatory. 

The 3I/ATLAS behaves differently from normal comets, which is intriguing scientists and researchers to study the space rock. Its approach to perihelion, then changing colors, non-gravitational acceleration, “no visible signs” of cometary tail, and now the first-ever radio signals have surprised them even more. 

According to Harvard scientist Avi Loeb’s writings on his blog, MeerKAT found radio absorption lines. They are basically faint dips in radio waves that happen when molecules in space absorb specific frequencies. These lines were caused by hydroxyl radicals (OH molecules). They detected two such lines at 1.665 GHz and 1.667 GHz. 

MeerKAT observed 3I/ATLAS on October 24, 2025, just a few days after it passed very close to the Sun. Earlier attempts (in September 2025) didn’t find anything. So this October detection is the first confirmed radio signal from 3I/ATLAS.

Scientists are studying the first-ever radio signal from 3I/ATLAS 

Thanks to MeerKat, this detection was possible. The radio telescope was able to detect the signals from the interstellar object when it was 3.76 degrees away from the Sun, almost seven times the Sun’s width. This was observed on October 24, 2025. And after that, the 3I/ATLAS appeared at its closest point, perihelion, on October 30, 2025.

The two radio signals reveal small shifts known as Doppler velocity shifts of approximately -15.6 km/s. This was the first successful detection of OH absorption from 3I/ATLAS. Avi Loeb wrote about the concept in his writings,

“The two lines revealed absorption at Doppler velocity shifts of -15.59 (+/-0.16) and -15.65(+/-0.17) kilometers per second, respectively. The full-width-at-half-maximum of the absorption lines were 0.88(+/-0.37) and 1.26(+/-0.40) kilometers per second, respectively.”

When MeerKAT observed it on October 24, the object’s motion was mostly sideways compared to the telescope’s line of sight. Because of this, the Doppler shift (the change in frequency due to motion) depended on how much of its 98 km/s total speed (30 km/s from Earth’s motion + 68 km/s from 3I/ATLAS itself) was directed toward or away from MeerKAT. Since the angle between its motion and MeerKAT’s view was 9.2°, only a small part of that speed caused the frequency shift that scientists measured.

According to the reports, researchers have already made a plan to detect more radio signals from 3I/ATLAS. On March 16, 2026, 3I/ATLAS will pass 53 million km from Jupiter, and NASA’s Juno spacecraft will try to listen for more radio signals from it at lower frequencies.

Loeb wrote, 

“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.”

The interstellar object (3I/ATLAS) discovered in 2025 is creating links to the Wow! Signal (a strange radio signal found in 1977 by astronomer Jerry Ehman).

Loeb believes that 3I/ATLAS came from almost the same direction in space as the Wow! Signal. 

“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,” Avi Loeb mentioned. 

He said the chance of that being random is only 0.6%, so the two may be connected.