Scientists detect radio signal from comet 3I/ATLAS
Scientists detected a radio signal from the interstellar comet 3I/ATLAS using the MeerKAT radio telescope in South Africa around its perihelion on October 29, 2025. The detected signal was caused by hydroxyl radicals (OH molecules) in the comet’s coma, which are produced naturally when sunlight breaks down water vapor outgassed from the comet. This outgassing process is a sign of cometary activity, confirming the object as an active comet, not an asteroid.
The radio emissions had frequencies around 1665 and 1667 MHz, known as the “water hole” range, which is significant in radio astronomy. The signal was unusual because instead of emission lines, it showed narrow-band absorption lines—something never seen in comets before—but this is still likely a natural phenomenon related to water molecules in the comet’s environment.
This discovery debunks earlier speculations about artificial or alien signals and highlights the comet’s active behavior during its close approach to the Sun. The comet 3I/ATLAS was observed to have intense water jets erupting like a “fire hose,” and the radio signal corresponds to these water-related chemical processes.
3I/ATLAS is notable as the third confirmed interstellar object to pass through our solar system, traveling at very high speed and originating from outside our solar neighborhood, possibly ejected from a distant star system billions of years ago. It will make its closest approach to Earth on December 19, 2025, at about 270 million kilometers, with no collision risk. Ongoing global monitoring and spectral analysis of 3I/ATLAS continue to provide valuable insights into interstellar comet activity and composition.
