Interstellar Object 3I/ATLAS: 3I/ATLAS may have come from a star system older than our sun, James Webb Telescope observations suggest

The interstellar visitor 3I/ATLAS is providing astronomers with a rare glimpse of material from outside our own Solar System. New observations from the James Webb Space Telescope have revealed rather unusual chemical signatures and tiny dusty ice grains around the object. The implication is that 3I/ATLAS may have formed in an ancient stellar nursery, many billions of years before our Sun came into being. Its trajectory could tell us something about how planets and their building blocks formed around other stars.

Could 3I/ATLAS be more than 7 billion years old?

A paper in Nature Astronomy looked at the gases being released by 3I/ATLAS using Webb's infrared instruments. The comet was observed in December 2025 when it was some 2.5 AU out from the Sun (i.e. 2.5 times farther from the Sun than Earth) and en route through the asteroid belt between Mars and Jupiter.


As the sun warmed the comet the frozen chemicals started to sublimate and form a coma. The scientists looked at the D/H ratio in the methane. Deuterium is a heavier isotope of hydrogen and the ratio of the two can tell you something about where and how an object formed.



The team found that 3I/ATLAS has by far the most heavy methane of any body in our solar system. Its measured ratio was 13 times higher than that of comet 67P/Churyumov-Gerasimenko, the only other local comet with a secure measurement of this signature. The researchers say the elevated ratio is consistent with ice forming in a very cold environment with low metal content and high exposure to cosmic rays.

One possibility is that the comet formed inside a region of gas and dust before a star was born. At temperatures around -263 degrees Celsius gases can freeze onto dust grains. These conditions can help preserve chemical signatures for long periods. Its low carbon-13 content also points towards an ancient origin. The researchers suggest that 3I/ATLAS may have come from a period when the universe had not yet been enriched by many generations of stars.

What Did Webb Discover Inside Its Icy Dust

A separate study led by Southwest Research Institute examined the comet’s water-ice grains. The team used Webb observations collected between August 2025 and April 2026.

Water ice normally leaves several identifiable patterns in infrared light. However, 3I/ATLAS showed a strong absorption feature near 3 microns, while two weaker features near 1.5 and 2.0 microns were barely visible or missing.

Researchers found that tiny grains about one micron or smaller made of water ice mixed with dust could explain the unusual pattern.

Dr. Silvia Protopapa, lead author of the study, said: “The grains of 3I/ATLAS are about the same size as those in our own comets. What seems to set them apart is how much dust is mixed into the ice.”

The grain properties appeared to change as the comet moved away from the Sun. Scientists have not yet determined whether this happened due to changing solar heating or because erosion exposed fresh material.

Why Does This Interstellar Visitor Matter

The findings suggest that some icy building blocks around other stars may share physical properties with objects in our own Solar System. Researchers say further Webb observations will help determine whether 3I/ATLAS is typical of interstellar visitors or an unusual example. For now, this object remains a rare opportunity to study material formed in another planetary system. Its chemical fingerprints may preserve a record of conditions from a time long before Earth and the Sun came into existence.

Information has been taken from:

Protopapa, S., et al. (2026). “JWST Reveals Refractory-rich Water Ice in Interstellar Comet 3I/ATLAS: Evidence for a Continuum of Grain Properties across Protoplanetary Disks.” The Astrophysical Journal Letters, 1011, L11. DOI: 10.3847/2041-8213/aea60d.