Scientists reveal new clues about the origin of the interstellar comet 3I ATLAS
It traveled billions of years from a cold, lonely corner of the galaxy. By the time it reached our solar system, it was already older than the Sun.
The comet that passed by us from another star last year likely originated in a cold, isolated corner of the galaxy that had not yet formed its own solar system, astronomers reported Thursday (April 24, 2026).
The comet 3I/ATLAS is only the third confirmed interstellar visitor and possibly the oldest. Scientists estimate it could be up to 11 billion years old, more than twice the age of the Sun.
The oldest known interstellar comet
A team led by the University of Michigan used the ALMA observatory in Chile's Atacama Desert to examine the comet last fall.
The wandering but harmless icy ball was discovered last summer, giving NASA and the European Space Agency enough time to point several space telescopes at it as it flew past Mars in October and made its closest approach to Earth in December.
It is now well beyond Jupiter, on its way to leaving our solar system for good, and remains visible only to specialists.
Deuterium, the key to its cold origin
In the study, published in Nature Astronomy, scientists claim to have detected extraordinarily high amounts of deuterium—or heavy hydrogen—in the comet's water. That suggests the comet originated in a considerably cooler place—even before the star of that solar system formed—than our own cosmic environment, explained Teresa Paneque-Carreno of the University of Michigan.
While our Sun may have been surrounded by other newly formed stars during its gestation, she noted, this comet's birth star might have been more isolated, resulting in less heating and cooler conditions.
Size, Speed, and Fate of 3I/ATLAS
The exact location of the comet's origin remains unknown.Observations from the Hubble Space Telescope place the size of its nucleus between 440 meters and 5.6 kilometers. It is receding at 220,000 kilometers per hour. Connecting all these “pieces of the puzzle can give us an idea of ??what planetary formation conditions were like in those early times,” Paneque-Carreno said in an email. 'Oumuamua and Borisov: The Other Stellar Travelers The first known interstellar object to venture into our celestial neighborhood—'Oumuamua—was discovered by a telescope in Hawaii in 2017. It was followed by comet 2I/Borisov in 2019, named after the Crimean amateur astronomer who first spotted it. FEW (AP, University of Michigan, Nature Astronomy)