Ancient interstellar comet may be oldest object ever observed in solar system

An interstellar comet that passed through the solar system may be around 12 billion years old, making it potentially the oldest object ever encountered by scientists, according to new observations from the James Webb Space Telescope (JWST).

Researchers studying comet 3I/ATLAS found unusual chemical signatures suggesting the object formed during the early history of the Milky Way, billions of years before the Sun and the solar system came into existence, The Guardian writes.

The comet, first detected on July 1, 2025, was quickly identified as an interstellar visitor because of its high speed and trajectory, indicating it originated beyond the solar system.

Scientists found that 3I/ATLAS releases significantly more carbon dioxide than water, unlike most comets formed within the solar system. Further analysis by JWST revealed exceptionally high levels of deuterium, a heavier form of hydrogen, and unusually low amounts of carbon-13, a heavier isotope of carbon.

According to NASA, the water ice in 3I/ATLAS contains roughly 30 times more deuterium than has been observed in any known solar system comet.

"This implies that 3I/ATLAS may have originated in a very cold system much earlier in the history of our galaxy," NASA said in a statement. "During its formation, the material that became incorporated into 3I/ATLAS was likely exposed to plenty of radiation, but not any long-term warmth that would have reprocessed its 'heavy water' ice, with deuterium, into the type of H2O ice we are familiar with on Earth."

Scientists also examined the comet's carbon composition. The object contains only trace amounts of carbon-13 relative to carbon-12, a finding that points to an extremely ancient origin.

"Almost all the carbon in the Milky Way is produced by stars more massive than the Sun. When those stars die, the carbon they produce through nuclear fusion is returned to the cosmos, to be incorporated in the next generation of stars and planets," said Jonti Horner, an astrophysicist at the University of Southern Queensland who was not involved in the research.

"But there's a twist," Horner explained. "As stars create carbon in their interiors, they also act to convert carbon-12 (the most common isotope) into carbon-13, through a process called 'hot bottom burning'. As time goes by, the fraction of all carbon in the galaxy that is carbon-13 is increasing."

Based on the isotope ratios, researchers estimate the comet formed about 12 billion years ago.

"To contain such a low abundance of carbon-13, 3I/ATLAS must have formed at a time when there was less carbon-13 compared to carbon-12 — roughly 12 billion years ago, during the earliest stages of our galaxy's history," Horner said.

Scientists say the discovery could help them better understand the chemical conditions that existed in the early Milky Way and provide clues about the ingredients needed for life elsewhere in the universe.

"For us as scientists, finding these rare isotopes is fascinating, but the bigger picture here is looking at the possibilities of prebiotic chemistry elsewhere in the galaxy," said Stefanie Milam of NASA's Goddard Space Flight Center, a co-author of the study. "So far, we know of only one place in the vast cosmos where chemical ingredients led to life — our solar system, our Earth. Analysis of these interstellar objects is a major step towards learning how common, or uncommon, the conditions for the evolution of life are in the universe."

Lead author Martin Cordiner said the comet offers a rare glimpse into a period of cosmic history that predates the formation of the Sun.

"This was a unique opportunity to study an ancient object from the distant galaxy, probably pre-dating our Sun and solar system," Cordiner said. "On the one hand, we get direct insight into that distant time and place, and on the other, we learn something about how unusual our own solar system may be."

By Aghakazim Guliyev