3I/Atlas
Astronomers say interstellar comet 3I/ATLAS is carrying chemicals and dust shaped by another star’s environment, based on new readings from space telescopes. NASA

Astronomers studying 3I/ATLAS, the third confirmed interstellar object ever recorded, say new data reveal that the comet carries material forged around a different star, offering an unprecedented peek into the chemical makeup of planetary systems beyond our own.

Discovered on 1 July 2025 by the ATLAS (Asteroid Terrestrial‑impact Last Alert System) survey telescope in Chile, 3I/ATLAS has a hyperbolic trajectory, confirming it is merely passing through the Solar System, never to return.

Scientists describe it as an icy body surrounded by a glowing cloud of gas and dust (a coma), typical of comets, yet its chemical signature is anything but typical.

Unusual Gas Composition

Infrared observations from the James Webb Space Telescope (JWST) show that the coma of 3I/ATLAS is dominated by carbon dioxide, with other volatile compounds such as water (H₂O), carbon monoxide (CO), OCS, water ice and dust also present, according to an article published on arXiv.

Measurements show that 3I/ATLAS has an unusually high amount of carbon dioxide compared with water, much more than what we usually see in comets from our Solar System.

Even more surprising, when scientists examined the comet's gases at its closest approach to the Sun, they found a lot of nickel but very little iron. This kind of nickel-to-iron ratio hasn't been seen in any other comet we know of.

Scientists think the weird mix of gases in 3I/ATLAS may be due to its having drifted through deep space for billions of years.

Out there, it's constantly hit by intense cosmic radiation. Over time, that radiation can change the chemicals on the comet's surface—for example, turning carbon monoxide into carbon dioxide—and leave behind a tough, weathered outer layer full of altered organic material.

In other words, what we're seeing now might not be the comet's original makeup when it formed around another star.

Its surface has likely been 'cooked' and reshaped by the harsh conditions of interstellar space, so it may no longer be the untouched, early-universe sample scientists were hoping for.

A Window into Distant Planetary Systems

Because 3I/ATLAS likely formed in a star system completely different from ours, its irregular chemical composition offers scientists a rare chance to compare how planetary formation and evolution may differ across the galaxy.

As one NASA summary puts it, this comet carries material 'forged around another star.'

The presence of abundant CO₂, water‑ice, reactive metals and dust suggests that the building blocks of planets—or at least small bodies—in other systems may vary considerably depending on local conditions in their protoplanetary disks, including temperature gradients, radiation exposure and chemical environment.

In effect, 3I/ATLAS serves as a kind of time capsule—possibly from a system far older than ours —carrying clues about how planetary systems form under different cosmic conditions.

No Threat — Just Spectacular Science

For those wondering whether such a visitor poses any danger to Earth: it does not. According to the space agencies tracking it, 3I/ATLAS will not come closer than about 270 million kilometres (around 1.8 astronomical units) from Earth.

Its trajectory will carry it out of the Solar System again, leaving only the wealth of data gathered to tell its story.

Why This Matters — And What Comes Next

The extraordinary compositions observed, especially the extreme CO₂ enrichment and the nickel‑over‑iron dominance, challenge existing models of comet formation and evolution.

Scientists are now rethinking how long‑residence interstellar objects might evolve chemically under cosmic ray processing, rather than preserving pristine material from their birth.

As 3I/ATLAS recedes toward interstellar space, astronomers are calling on global observatories and citizen‑scientist networks to continue tracking and analysing its fading tail.

Researchers involved in upcoming missions, such as the Comet Interceptor, say the data from this encounter will be invaluable for preparing for future interstellar visitors and, maybe, even a direct rendezvous one day.