SOLAR SYSTEM — A study published in the journal Nature in 2025 indicated that interstellar comet 3I/ATLAS formed in an extremely cold environment near stars in their birth stages. Researchers utilized isotopic data from the James Webb Space Telescope and the ALMA observatory in Chile to reach this conclusion. 3I/ATLAS is the third interstellar object observed by humans and was discovered in July 2024, passing the Sun and Earth in 2024.

Martin Cordiner, a researcher at NASA's Goddard Space Flight Center and lead author of the study, stated, "maybe it's the oldest object to have been observed in our solar system." The isotopic evidence indicated 3I/ATLAS formed in an environment with a temperature of minus 243 degrees Celsius. The comet contains 10 times more deuterium, a type of hydrogen found in heavy water, than comets originating in the solar system.

Cordiner explained, "That high abundance of heavy water can only really happen, according to our understanding of astrochemistry, in a very cold environment." The study also suggested a lack of chemical enrichment on 3I/ATLAS, which indicates its formation occurred close to nascent stars. Darryl Seligman, an astronomer at Michigan State University not involved in the research, noted, "Until these measurements we could only really dream about getting this kind of information for an interstellar object."

NASA dismissed the possibility of an alien origin for 3I/ATLAS. The Search for Extraterrestrial Intelligence Institute also stated it found no evidence of extraterrestrial technology on the comet. Peter Veres, an astronomer involved in identifying 3I/ATLAS at the International Astronomical Union's Minor Planet Center, said, "The comet is now leaving the solar system and will never return, so future observations will become increasingly difficult."

Past observations of interstellar objects 1I/'Oumuamua in 2017 and 2I/Borisov in 2019 did not yield isotopic evidence because they were not bright enough. A NASA image released in November 2025 showed 3I/ATLAS approximately 180 million miles from Earth. Images from two Mars orbiters in October 2025 showed the comet about 18,641,135 miles from Mars. An image from September 2025 displayed the tail of 3I/ATLAS. On July 21, 2025, when the Hubble Space Telescope captured an image of 3I/ATLAS provided by NASA and the European Space Agency, the comet was 277 million miles from Earth. Cordiner indicated, "This is just the beginning of an exciting new field, we've got a lot more to learn about these things and what they can tell us about our galaxy."