Interstellar Comet 3I/ATLAS Might Be the Oldest Object Ever Seen in Our Solar System, a Study Suggests

Based on the composition of gases spewed by the icy space rock, researchers estimate that our guest might be up to 12 billion years old—about three times the age of the solar system

Michele Debczak | Correspondent

June 24, 2026 3:55 p.m.

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Our latest known interstellar visitor, comet 3I/ATLAS, is currently making its way out of the solar system, after passing by the sun late last year. Scientists have been racing to study the rare guest with the glimpses they’ve gotten via ground- and space-based telescopes.

Now, a team has determined that the comet may have formed as far back as 12 billion years ago, making it about three times the age of our solar system and nearly as old as the universe. The findings were published in the journal Nature on June 22.

3I/ATLAS might be “the oldest object to have been observed in our solar system,” says study co-author Martin Cordiner, an astrochemist at NASA’s Goddard Space Flight Center, to the Agence France-Presse’s Daniel Lawler.

The famous comet was discovered in July 2025 when a NASA-funded telescope in Chile, part of the Asteroid Terrestrial-impact Last Alert System (ATLAS), spotted it zooming at about 137,000 miles per hour. Its speed and trajectory hinted that the object came from far beyond our sun’s domain, making it our third known interstellar visitor after 1I/‘Oumuamua in 2017 and 2I/Borisov in 2019.

But 3I/ATLAS has stood out among its interstellar peers as the biggest, with an icy core estimated to be between 1,400 feet and 3.5 miles wide, and the brightest. Its brightness made it a great target for telescopes, Cordiner tells Science’s Hannah Richter.

Cordiner and his colleagues used the James Webb Space Telescope and the Atacama Large Millimeter/submillimeter Array telescope in Chile to stare at the comet last December as it spewed gases due to the sun’s heat.

Based on the gases’ ratio of two forms of carbon, the researchers estimate that the icy space rock is about 10 billion to 12 billion years old, meaning it was born just a few billion years after the Big Bang. That age hints it formed during a time called “cosmic noon,” when the pace of star formation peaked.

The data also revealed that 3I/ATLAS contains around 30 times the amount of deuterium, a form of hydrogen that is “heavy” because it contains a neutron, as solar system comets, hinting that our guest came from an extremely frigid place. The discovery echoes work published in April that suggests 3I/ATLAS may have been born before the host star of its home planetary system formed. The researchers behind the new study suspect the comet took shape in an environment that was at or below -405 degrees Fahrenheit, making it one of the coldest objects ever seen in the solar system.

Scientists are excited about the findings and what they represent.

“Until these measurements, we could only really dream about” getting this kind of data on an interstellar object, Darryl Seligman, an astrophysicist at Michigan State University who was not involved in the study, tells the AFP. Although 3I/ATLAS’s age is still just an estimate, he notes, it’s “a safe bet that it’s older than anything that formed in the solar system.”

The biggest opportunity with the interstellar comet, however, is getting a snapshot of chemistry elsewhere in the universe and seeing whether it could possibly lead to life, says study co-author Stefanie Milam, an astrochemist at NASA Goddard, in a statement.

“So far, we know of only one place in the vast cosmos where chemical ingredients led to life—our solar system, our Earth,” she says. “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.”

Michele Debczak | Read More

Michele Debczak is a writer and editor based in Brooklyn, New York. She appears in seasons four through six of History Channel’s “The Food That Built America,” and her work has been featured in Mental Floss, IndieWire, Eater and Vice.