Interstellar comet 3I/ATLAS has 13 times more deuterium than a famous Solar System comet, hinting at its 7-billion-year-old origins before Sun was born

Interstellar object 3I/ATLAS is a fascinating interstellar comet that traveled into our Solar System from beyond its boundaries. First reported on July 1, 2025, by the ATLAS survey telescope in Chile, it became the third confirmed interstellar object discovered passing through our cosmic neighborhood. Scientists have now found out that the exosolar system that formed 3I/ATLAS may have assembled it more than 7 billion years before our Sun ignited into life – possibly even before 3I/ATLAS's own star erupted, according to Science Alert.

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What did the scientists find out about Interstellar object 3I/ATLAS?

According to a new study published in the journal Nature Astronomy, scientists analyzed the gases released by interstellar comet 3I/ATLAS. The research team, led by scientists from NASA's Solar System Exploration Division, used the James Webb Space Telescope to study the comet in late December 2025, when it was about 2.5 times farther from the Sun than Earth. At this distance, heat from the Sun causes the comet's frozen chemicals to turn into gas, making its atmosphere, known as a coma, grow larger.


The scientists focused on the comet's deuterium (a heavier form of hydrogen)-to-hydrogen (D/H) ratio and measured its amount compared with regular hydrogen can help scientists understand where and how an object formed.

They specifically studied this ratio in methane, one of the gases released by the comet. This helped them investigate the chemical makeup of the frozen material from which 3I/ATLAS formed. The findings were unusual as the 3i/atlas comet contained far more heavy methane than any known object in our Solar System.

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Its deuterium-to-hydrogen ratio was also 13 times higher than that of comet 67P/Churyumov-Gerasimenko, the only other comet in our Solar System with a confirmed measurement of this kind. That measurement was made by the European Space Agency's Rosetta spacecraft.

"The elevated D/H ratio for methane in 3I/ATLAS is consistent with the hypothesis that its ices formed in a cold, low-metallicity interstellar or protostellar environment under a high cosmic ray irradiation rate," the researchers explain.

Why is interstellar comet 3i/atlas so precious?

According to the Journal, the 3i/atlas is a pristine sample ejected from the hidden depths of an ancient cosmic nursery, possibly around one of the Milky Way's oldest stars, and delivered directly to our doorstep by the caprices of gravity. By studying the gases released by 3I/ATLAS, astronomers were able to investigate how and where the comet may have formed.

The chemical signatures suggest that the comet may have been exposed to high levels of radiation. Scientists also believe it could have formed inside a prestellar core — a dense, extremely cold cloud of gas and dust that represents the earliest stage of star formation. These clouds are protected from much of the starlight around them and can preserve frozen material for billions of years.

Another important clue comes from the comet's low carbon-13 content. This suggests that 3I/ATLAS could have formed in the early universe, before several generations of stars had released heavier elements into space through nuclear reactions and supernova explosions.

The comet poses no threat to Earth and 3I/ATLAS reached its closest approach to the Sun around Oct. 30, at a distance of 1.4 au (about 130 million miles or 210 million km) — just inside the orbit of Mars. The comet’s name comes from its status as the third confirmed interstellar comet, meaning it originated outside the solar system, and the telescope that first spotted it, the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System).