MeerKAT radio observations on October 24 detected hydroxyl (OH) absorption lines from interstellar object 3I/ATLAS, indicating water is being broken down by sunlight. These radio results, together with earlier ultraviolet OH detections from Swift and infrared data from JWST (which found mostly CO₂ ice and ~4% water), support the interpretation that 3I/ATLAS is an active interstellar comet rather than an exotic artifact. Researchers note an unexpectedly high water-loss rate at ~3 AU, and another close approach near Jupiter on March 16, 2026 offers more opportunities for study.
MeerKAT Detects Water Signature from Interstellar Visitor 3I/ATLAS — Evidence Favors Cometary Origin
MeerKAT radio observations on October 24 detected hydroxyl (OH) absorption lines from interstellar object 3I/ATLAS, indicating water is being broken down by sunlight. These radio results, together with earlier ultraviolet OH detections from Swift and infrared data from JWST (which found mostly CO₂ ice and ~4% water), support the interpretation that 3I/ATLAS is an active interstellar comet rather than an exotic artifact. Researchers note an unexpectedly high water-loss rate at ~3 AU, and another close approach near Jupiter on March 16, 2026 offers more opportunities for study.
11:54 PM, 11/11/2025Science
MeerKAT finds hydroxyl absorption from interstellar object 3I/ATLAS
On October 24, astronomers using South Africa’s MeerKAT radio telescope detected radio absorption lines from hydroxyl radicals (OH) associated with the interstellar object 3I/ATLAS. Hydroxyl is a known photodissociation product of water: when sunlight breaks water molecules apart, OH is produced and can be seen in radio and ultraviolet observations. The detection followed two earlier, unsuccessful radio attempts in September.
The team described the observation as radio absorption by OH; Harvard astronomer Avi Loeb called it the "first radio detection of 3I/ATLAS" in a blog post. While Loeb has at times floated unconventional explanations for the object’s origin, the new radio and prior ultraviolet results are consistent with the simpler interpretation that 3I/ATLAS is an interstellar comet releasing water as it nears the Sun.
Previous measurements provide a mixed picture: infrared spectra from NASA’s James Webb Space Telescope indicated the object is dominated by carbon dioxide ice, with water contributing roughly four percent of its mass, while ultraviolet spectra from NASA’s Neil Gehrels Swift Observatory had already revealed OH gas. Together, the UV and new radio detections strengthen the case that water — even if a minor constituent by mass — is actively being released and broken down by sunlight.
“When we detect water — or even its faint ultraviolet echo, OH — from an interstellar comet, we’re reading a note from another planetary system,” Auburn University physicist Dennis Bodewits told the BBC. “It tells us that the ingredients for life’s chemistry are not unique to our own.”
The team also reported a substantial water-loss rate despite 3I/ATLAS being at roughly three astronomical units from the Sun, a distance where typical Solar System comets are usually much less active. That elevated activity could reflect differences in composition or surface properties compared with familiar comets from our own system.
Observers will have additional chances to study the object before it exits the Solar System. According to Loeb, on March 16, 2026, 3I/ATLAS is expected to pass within about 53 million kilometers of Jupiter. At that time, NASA’s Juno spacecraft could attempt to search for low-frequency radio emission from the object using its dipole antenna in the 50 Hz to 40 MHz range.
Why this matters
Detecting water or its chemical byproducts in an interstellar object gives astronomers a direct probe of the volatile inventory of another planetary system. Continued multiwavelength observations (radio, ultraviolet, infrared and optical) will help refine estimates of composition, activity levels, and how interstellar small bodies compare with comets formed around the Sun.