Scientists have found that the interstellar comet 3I/ATLAS, only the third known object from outside the solar system to pass through it, is an exceptionally ancient visitor that likely formed 10 to 12 billion years ago in a primordial planetary system. Researchers said its chemical composition is unlike anything previously observed in the solar system, offering fresh insights into the conditions in which it was formed.
The comet, measuring about 2.6 km in diameter, is believed to be the oldest-known object to travel through the solar system. The findings, published in the journal Nature, are based on observations made using the James Webb Space Telescope, Reuters reported.
Lead author Martin Cordiner, a planetary scientist and astrochemist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said the comet probably formed in an environment far colder than the one that produced Earth and the rest of the solar system around 4.5 billion years ago. Researchers estimate its birthplace had temperatures of about minus-243 degrees Celsius before the object was ejected from its home planetary system and began its long journey through space.
"We have never before seen an object like 3I/ATLAS," Cordiner said.
Unique chemical signature reveals ancient origins
Researchers analysed the ratios of different isotopes of hydrogen and carbon in 3I/ATLAS to understand the environment in which it formed. Hydrogen isotopes revealed clues about the temperature and radiation levels of its birthplace, while carbon isotope ratios helped identify the nature of the interstellar gas cloud from which the comet and its planetary system emerged.
The comet's water contains about 30 times more deuterium, a hydrogen isotope, than comets found in the solar system. Its carbon isotope ratios also differ from those observed in solar system objects, interstellar clouds and planet-forming discs around nearby young stars.
"Our James Webb Space Telescope observations tell us that the planet-forming environment of 3I/ATLAS's host system was distinct from our own solar system. It was likely colder, and less metal rich, while being more heavily irradiated by UV and cosmic rays," Cordiner said.
Despite its ancient and distant origin, researchers found the comet is rich in organic molecules containing carbon, hydrogen, nitrogen, oxygen and sulfur.
"This shows that despite a cold and distant origin, the volatile elements for life as we know it were abundant in this distant planet-forming disk," Cordiner said.
The carbon composition suggests the comet formed up to 12 billion years ago during a period of intense star formation, when the universe was only about 13% of its current age.
Journey through the solar system continues
Scientists believe 3I/ATLAS most likely originated in the Milky Way, although they cannot rule out the possibility that it came from another galaxy.
"I had anticipated that intergalactic distances were too vast, but in fact it could take as little as a billion years for a fast interstellar object to get here from our nearest galactic neighbors, the Magellanic Clouds," Cordiner said.
Researchers said the comet may have been expelled from its planetary system through gravitational interactions with planets, although a collision is also considered a possible explanation.
The only other known interstellar objects observed passing through the solar system are the comets 1I/'Oumuamua, detected in 2017, and 2I/Borisov, discovered in 2019.
3I/ATLAS is currently approaching Saturn's orbit and is expected to travel beyond Pluto's orbit in 2029 before leaving the outer boundary of the solar system around 2035.
Researchers also dismissed suggestions that the object could be an alien spacecraft.
"While good scientists always remain open to updating their understanding, we take great care to weigh the evidence for each hypothesis," Cordiner said. "In this case, the evidence was clear from a very early stage that we were looking at a comet-like object, and over time that interpretation has been confirmed by subsequent observations."
