3I/ATLAS Comet Unveils Unprecedented Radio Signal: Experts Are Baffled

Astronomers using South Africa’s MeerKAT telescope detected a narrow-band signal at 1665 and 1667 MHz from interstellar comet 3I/ATLAS on October 24, 2025. Found in the so-called ‘water-hole’ range, the unprecedented absorption signature marks the first time a comet-like object has produced such a radio signal. (Credit: Atlastellar Instagram Account Photo)

On 24 October 2025, South Africa's MeerKAT radio telescope detected a signal that has left astronomers stunned. The interstellar comet 3I/ATLAS produced a narrow-band hydroxyl absorption at 1665 and 1667 MHz, a range known as the 'water hole.' This quiet region of the spectrum has long been considered significant in the search for extraterrestrial intelligence. Yet no comet-like object has ever produced such a signature before.

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