A comet tearing through the inner solar system at roughly 58 kilometers per second formed between 10 and 12 billion years ago, according to isotopic measurements published this year. That would make the object, designated 3I/ATLAS, more than twice as old as the Sun and everything orbiting it. NASA has confirmed the comet is interstellar, only the third such visitor ever identified. The age estimate itself comes not from the agency but from independent research teams whose findings place the comet’s origins in an era when the Milky Way was still forging its earliest generations of stars.
For planetary scientists, the implications are striking. 3I/ATLAS is a frozen time capsule carrying chemical fingerprints from billions of years before Earth existed, and it is close enough, for a few months, to study with the best telescopes humanity has.
Discovery and confirmation
The NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey first flagged the object, and the discovery was reported to the International Astronomical Union’s Minor Planet Center on July 1, 2025. Within days, NASA’s Planetary Defense Coordination Office published a formal notice classifying 3I/ATLAS as interstellar. The classification rests on the comet’s hyperbolic trajectory, a path so open and fast that it could not have originated around the Sun. Its excess velocity relative to our star, about 58 km/s, rules out any gravitationally bound orbit in the solar system.
On July 21, 2025, the Hubble Space Telescope captured a direct image of the comet, revealing a diffuse coma of gas and dust surrounding a small, still-unresolved nucleus. That image, along with follow-up observations from ground-based facilities, gave astronomers their first detailed look at the object’s brightness, dust production rate, and outgassing behavior.
3I/ATLAS follows 1I/’Oumuamua, detected in 2017, and 2I/Borisov, spotted in 2019. But it differs from both predecessors in important ways. ‘Oumuamua showed no visible coma and was likely a rocky or icy fragment with minimal outgassing. Borisov looked much more like a conventional comet but was already on its way out of the solar system by the time telescopes caught up. 3I/ATLAS, by contrast, was detected early enough in its inbound arc to allow months of observation as it approached perihelion, giving researchers a longer window to collect spectra and monitor how its surface responds to solar heating.
Two paths to an ancient age
Two independent lines of analysis converge on the conclusion that 3I/ATLAS is extraordinarily old, though they arrive there by different routes.
The first is kinematic. A study published in The Astrophysical Journal Letters traced the comet’s velocity backward through statistical models of stellar encounters in the Milky Way’s disk. The result was a probable age window of roughly 3 to 11 billion years. At the low end, the comet would be younger than our own solar system. At the high end, it would predate the Sun by more than six billion years.
The second approach is chemical. A preprint circulated in early 2026 examined carbon isotopic ratios in the gases streaming off 3I/ATLAS and interpreted them through Galactic chemical evolution (GCE) models, which track how the relative abundances of isotopes in the Milky Way have shifted over cosmic time. That analysis placed the comet’s formation at roughly 10 to 12 billion years ago, deep in the galaxy’s youth. A separate peer-reviewed paper in Nature Astronomy analyzed the deuterium-to-hydrogen ratio in the comet’s water vapor and reached broadly compatible conclusions, finding the isotopic signature consistent with material that predates the solar system by billions of years.
The overlap between the kinematic upper bound and the isotopic midpoint, both clustering near 11 billion years, is what gives the headline figure its weight. But overlap between two uncertain measurements does not erase the uncertainty in either one. The kinematic range spans eight billion years. The GCE models depend on assumptions about nucleosynthesis rates, stellar density, and galactic mixing that are themselves subjects of active research. And the carbon-isotope preprint has not yet completed formal peer review.
What NASA has and has not said
A point of clarity matters here. NASA has confirmed that 3I/ATLAS is interstellar. The agency’s public communications describe the discovery, the observational campaign, and the comet’s trajectory. No official NASA statement or press release has directly endorsed the 11-billion-year age estimate. That figure originates from independent research teams whose work is published or in preprint form. NASA’s confirmation of the comet’s origin beyond the solar system is robust. The specific formation date is a scientific inference, not an agency certification.
As of June 2026, no detailed carbon or oxygen isotopic data from NASA instruments have been released through official channels. Long-term trajectory predictions, including whether a future spacecraft mission could intercept the comet before it exits the inner solar system, have not appeared in agency planning documents. And no NASA-affiliated researchers have issued public statements interpreting what the comet’s age means for models of early planet formation.
What the chemistry reveals about planet formation
Spectroscopic observations from ground-based telescopes have detected water vapor, carbon-bearing molecules, and dust in the comet’s coma. Broadly, that inventory resembles what astronomers see in comets native to our own solar system, objects like 67P/Churyumov-Gerasimenko, which the European Space Agency’s Rosetta mission studied up close.
That similarity is itself a finding. If a comet born around a star 10 or 11 billion years ago carries roughly the same volatile species as one that formed alongside the Sun 4.6 billion years ago, it suggests that the basic recipe for icy planetesimals, water ice mixed with carbon compounds and silicate dust, is not unique to our corner of the galaxy or our epoch. Planet-forming disks separated by billions of years and potentially very different stellar environments may still produce comparable building blocks.
But the details could diverge in ways that matter. Subtle differences in isotopic ratios, the relative abundances of heavy versus light versions of elements like carbon, nitrogen, and oxygen, encode information about the nuclear reactions inside the stars that seeded the comet’s birth cloud. Pinning down those ratios with higher precision is the next major observational goal, and it is one reason astronomers are pushing for additional telescope time before 3I/ATLAS recedes from view.
Open questions and what comes next
Even basic physical properties of the comet remain loosely constrained. Estimates of its nucleus size depend on assumptions about albedo and activity level; small changes in either parameter shift the inferred diameter significantly. Rotation rate, internal structure, and surface composition are essentially unknown. Those gaps matter because they feed directly into models of how a small icy body could survive for billions of years in interstellar space, exposed to cosmic rays and micrometeoroid bombardment, without being ground down to nothing.
Several questions will shape the next phase of research. Can the James Webb Space Telescope or large ground-based observatories capture higher-resolution spectra before the comet fades? Will refined GCE models, incorporating new data from stellar surveys like Gaia, shift the expected isotopic ratios for early epochs and with them the inferred age? And is there any realistic trajectory for a flyby mission, or will 3I/ATLAS, like its predecessors, slip away before spacecraft technology can catch up?
For now, the most accurate summary is also the most striking. 3I/ATLAS is an ancient interstellar comet, almost certainly billions of years older than the Sun, carrying chemistry from a chapter of galactic history that no solar system object can access. It is passing through our neighborhood briefly, offering a narrow window to study material from a time when the Milky Way was young. Whether its formation date ultimately settles closer to 8 billion years ago or 12 billion, the comet has already expanded what astronomers know about the raw ingredients that drifted between stars long before our own planet took shape.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
