‘Interstellar messenger’ 3I/ATLAS could be nearly as old as the universe itself, James Webb telescope observations reveal
Interstellar comet 3I/ATLAS is up to 12 billion years old and unlike anything found in our solar system, new James Webb Space Telescope (JWST) suggest.
Comet 3I/ATLAS became a celestial celebrity last year after the interstellar visitor was discovered while racing down our cosmic neighborhood. Soon after, online speculation suggested that the space rock could be a alien spaceship. However, most astronomers are convinced that 3I/ATLAS is a comet from a unknown star system.
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The researchers already knew, thanks to the speed and trajectory of the comet, that it was potentially the the oldest comet ever seen. Previous estimates put the comet’s age at between 3 and 11 billion years. The new findings further clarified the age and origin of the comet by examining isotopic measurements taken by JWST when the comet flew past Earth in December 2025.
“They show that the isotopic composition of 3I/ATLAS is very different from that of comets in the Solar System and suggest that it probably formed 10 to 12 billion years ago.” Romain Maggioloa researcher at the Royal Belgian Institute for Space Aeronomy who was not involved in the study, told Live Science in an email. “In other words, 3I/ATLAS formed in a stellar environment different from ours, not only elsewhere in space, but also at a much earlier time in the history of the Milky Way.”
Comet 3I/ATLAS is only the third interstellar object ever recorded in our solar system. The space rock, which Hubble Space Telescope Observations suggested is between 1,400 feet (440 meters) and 3.5 miles (5.6 kilometers) wide, zoomed through our solar system at about 137,000 mph (221,000 km/h) last year before launching around the sun.
After reaching its closest point to our star, known as perihelion, on October 29, 2025, the comet then made its turn. closest approach to Earth on December 19, when it was about 168 million miles (270 million kilometers) from our planet. JWST made the observations that were analyzed in the new study a few days later, on December 22.
A relic of the ancient universe
Comets heat up as they get closer to stars, causing the ice on their surfaces to sublimate into gas. By studying the composition of this gas, researchers can begin to understand what they are made of and the conditions under which they formed.
The authors of the new preprint examined the ratio of isotopesor versions of elementsin material degassed by 3I/ATLAS. They found that the comet’s water is more enriched in deuterium, a heavier isotope of hydrogen, than any comet previously studied, while its ratio of carbon isotopes also exceeded levels normally seen in our solar system.
The results offer clues to the conditions under which ancient planetary systems forged the comet during the early years of the Milky Way.
“If 3I/ATLAS is indeed as old as this study suggests, the large amounts of volatile molecules it contains indicate that rich prebiotic chemistry could have already occurred in star-forming regions very early in the history of our Galaxy,” Maggiolo said.
The results also indicate that the comet formed in a cold environment of around 30 kelvins (minus 406 degrees Fahrenheit or minus 243 degrees Celsius), likely in a dense, well-protected protoplanetary disk, according to the study.
Although the study is still in the pre-publication stage, Maggiolo, who has studied comet 3I/ATLAS as part of his own research, did not have any major concerns about it. The new measurements help researchers “better understand this interstellar messenger,” he said.
Josep Trigo-Rodríguezprincipal investigator of the Asteroids, Comets and Meteorites Research Group at the Institute of Space Sciences (CSIC/IEEC) in Spain, who has already identified eruption of “ice volcanoes” on comet 3I/ATLASdescribed the new findings as a good compilation of scientific results, using different techniques from recognized experts.
“This manuscript shows that interstellar comets are unique bodies capable of sampling distant regions of our Milky Way galaxy,” Trigo-Rodríguez said in an email to Live Science.
Chances are, researchers will never know which star system gave rise to comet 3I/ATLAS. The comet has probably been traveling through space for billions of years and has come a very long way during this time. at Maggiolo own research found evidence that the object is extremely irradiatedwith all that time spent in space exposing it to cosmic rays that could have fundamentally altered its chemical composition, making its origins more difficult to decipher.
“The isotopic composition of the materials degassed by 3I/ATLAS constitutes a crucial new piece of the puzzle,” Maggiolo said. “But the puzzle is far from finished!”
Finding these puzzle pieces is a race against time for astronomerswhile comet 3I/ATLAS is leaving the solar system. It is currently passing in front of Jupiter, where it should approach closest on Sunday March 15. The comet will approach about 54 million kilometers from the gas giant, much closer than it has been to Earth.
The interstellar traveler will then continue its journey away from us, crossing the orbit of Saturn in July, the orbit of Uranus in April 2027 and the orbit of Neptune in March 2028. You can track the comet using NASA’s sensor. Eyes on the solar system simulation of the comet’s trajectory.
