Interstellar Comet 3I/ATLAS found releasing water in space far from the Sun, NASA, ESA confirm

Water Found on Interstellar Comet 3I/ATLAS, ESA and NASA Confirm (Image: NASA)

A frozen traveller from another star system has surprised astronomers. Scientists have detected signs of water on comet 3I/ATLAS, only the third known interstellar object to visit our solar system.

How was the comet observed near Mars?

The European Space Agency’s ExoMars Trace Gas Orbiter (TGO) and Mars Express turned their instruments towards 3I/ATLAS as it made its closest approach to Mars on October 3. The comet passed within 18.6 million miles (30 million kilometres) of the planet. While Mars Express could not spot the faint object, ExoMars TGO managed to capture a sequence of images showing it racing through space at nearly 130,000 miles per hour (210,000 kilometres per hour).

ExoMars TGO image of comet 3I/ATLAS (Image: ESA)

How did scientists confirm water on 3I/ATLAS?

Researchers from Auburn University, using NASA’s Neil Gehrels Swift Observatory, detected the ultraviolet signature of hydroxyl—a byproduct of water vapour. The study, led by Zexi Xing, confirmed that the comet carries traces of water. Observations revealed a sharp rise in hydroxyl emissions between July and mid-August, from 2.2 × 10³⁰ to 4.2 × 10³⁰ molecules, meaning the comet releases about 40 kilograms of water every second.

Scientists estimate that nearly 8% of the comet’s surface, about 7.8 square kilometres, is actively venting vapour. Most comets show only three to five per cent activity.  This dramatic outburst indicates that 3I/ATLAS must be an ice-dominated surface or embedded with dust particles which continually release water once they've escaped the nucleus.

Why is this finding significant?

What makes this finding unusual is that 3I/ATLAS was shedding water while three times farther from the Sun than Earth. At that distance, temperatures are too cold for normal sublimation. Researchers believe tiny ice grains ejected into space are warmed by faint sunlight, releasing vapour—a rare behaviour among comets.

This finding provides researchers with an interesting glimpse of the potential for life's building blocks to journey between stars. Comets such as 3I/ATLAS may serve as conveyors, transporting lowly water and organic compounds between star systems, potentially dispersing the materials necessary for life.

The comet's chemistry further contributes to its mystique. Unlike other known comets, 3I/ATLAS is rich in water but low in cyanogen, suggesting it may have formed near a young, metal-poor star.

As lead researcher Zexi Xing said, “Each interstellar comet that has come by so far has been a surprise. ‘Oumuamua was dry, Borisov was carbon monoxide-rich, and now ATLAS is shedding water where we didn’t expect it.”

The research, reported by thebrighterside, highlights how interstellar visitors like 3I/ATLAS continue to challenge what scientists know about planet and comet formation around distant stars.