Interstellar comet nearly as old as universe

A new study suggests that interstellar comet 3I/ATLAS may be among the oldest objects ever detected—potentially around 12 billion years old. That would make it far more ancient than our own solar system, which formed roughly 4.5 billion years ago, and nearly as old as the universe itself.

Spotted in 2025, 3I/ATLAS is the third interstellar visitor astronomers have identified passing through our solar system. It follows 1I/ʻOumuamua, discovered in 2017, and 2I/Borisov, which showed up two years later. Each object originated somewhere else entirely—rocks ejected from their home systems by gravitational interactions and sent wandering through interstellar space.

Researchers have used both the James Webb Space Telescope and the ground-based Atacama Large Millimeter/submillimeter Array in Chile to study gas streaming off the comet as sunlight vaporizes its icy interior. Chemical isotopes locked in that gas act as a kind of fingerprint, preserving information about where and when the object originally formed.

Carbon Isotopes Point to Extreme Age

A paper in Nature—first posted as a preprint in March—used carbon isotope ratios to estimate the comet’s age. The results pushed the timeline back significantly from earlier estimates.

At around 12 billion years, the object would have formed when the universe was barely two billion years old. The cosmos itself is approximately 13.8 billion years old, meaning 3I/ATLAS has been drifting through space for nearly the entire history of everything. Its birth predates our sun by more than seven billion years.

Deuterium Levels Hint at a Colder Home

The analysis also found that 3I/ATLAS carries unusually high concentrations of deuterium, a heavy form of hydrogen that contains one neutron in addition to its proton. Raised deuterium levels in cometary material typically indicate formation in very cold environments—colder than anything found in our own solar system’s comet reservoirs.

That detail aligns with other recent findings suggesting the region where 3I/ATLAS originated was far chillier than the space around our young sun. The comet’s composition doesn’t match local space rocks in several respects, and scientists are beginning to wonder whether our neighborhood might be the outlier.

Cyrielle Opitom, an astronomer at the University of Edinburgh and a co-author of the paper, said the results fit into a growing picture. Our solar system’s comets have been the only ones available to study for centuries, and they may not represent what’s normal elsewhere in the galaxy. The universe, it seems, might be stranger than we assumed.