Hydroxyl Detection by MeerKAT Confirms Natural Origin of Interstellar Comet 3I/ATLAS

The South African MeerKAT radio telescope has provided definitive evidence confirming the natural genesis of the interstellar visitor designated C/2025 N1 (ATLAS), known widely as comet 3I/ATLAS. This crucial observation centers on the unambiguous detection of hydroxyl (OH) absorption lines, registered at the 1665 MHz and 1667 MHz radio frequencies, which are characteristic signatures of active cometary outgassing.

The object first entered observational range on July 1, 2025, cataloged by the ATLAS survey instrument in Chile. Its trajectory immediately suggested an interstellar provenance, marking it as the third such object identified after 1I/’Oumuamua in 2017 and 2I/Borisov in 2019. The presence of these hydroxyl radicals signifies the fundamental process of sublimation, where the comet’s icy core transforms directly into gas as it nears the Sun. The specific radio signatures were observed by MeerKAT on October 24, 2025, just five days before the comet reached perihelion. Earlier scans conducted on September 20 and 28, 2025, proved inconclusive, likely because the comet had not yet achieved sufficient solar proximity to generate a strong signal.

Astrophysicist Avi Loeb, who had previously examined alternative hypotheses regarding 3I/ATLAS’s nature, acknowledged the significance of the hydroxyl detection. His current focus shifts to continuous monitoring to ascertain if the rate of OH production remains consistent or shows intermittent fluctuations. This ongoing inquiry is vital for mapping the internal structure and volatile composition of these visitors from beyond the solar system's established boundaries. Interstellar comets offer a unique comparative window into the chemical makeup of other stellar nurseries, as their volatile inventories can differ markedly from objects formed within our own solar nebula.

The celestial body is projected to reach its closest passage to Earth on December 19, 2025, at a distance of approximately 1.8 astronomical units, or about 270 million kilometers. This upcoming alignment presents an extraordinary opportunity for observers worldwide to witness this transient visitor from another star system. The clarity of the data now obtained allows the scientific community to concentrate its collective attention on the next phase of discovery, moving forward with shared insight into comparative cosmic chemistry.