By BlueShift | 2026-06-26

Interstellar comet 3I/ATLAS caused a global sensation when it was first observed close to a year ago by NASA's ATLAS survey telescope in Río Hurtado, Chile, as it raced through our Solar System at speeds that reached up to 150,000 mph.

Propelled by its interstellar momentum, the comet hurtled into the inner Solar System from deep space, passing through the asteroid belt between Mars and Jupiter, where it reached its closest point to our Sun last October 29.

The comet -- given the 3I designation as it is just the third confirmed interstellar object ever to pass through our Solar System -- then whizzed past Venus before passing behind the Sun in December and heading back into deep space.

As the interstellar visitor passed the Sun, the heat vaporized its ancient ice, giving it an unusually bright, glowing coma and very short tail.

The comet's appearance has been similarly illuminating, offering astronomers a rare opportunity to study such an object and giving NASA's ATLAS (asteroid terrestrial-impact last alert system) network one of its most impressive findings.

(The network's five telescopes, which together achieve full coverage of global skies, are positioned in Hawaii, South Africa and Spain, as well as in Chile.)

In a study published June 22 in the journal Nature, a team of astronomers reveal that 3I/ATLAS could be up to 12 billion years old -- close to three times older than our Solar System, which likely formed around 4.5 billion years ago.

"When interpreted with respect to models for Galactic chemical evolution, the carbon isotopic composition implies that 3I/ATLAS may have accreted as long ago as 12 billion years, following a period of intense, early star formation."

"3I/ATLAS thus represents a preserved fragment of an ancient planetary system," according to the study's abstract.

It is possible that the comet is "the oldest object to have been observed in our Solar System," the study's lead author Martin Cordiner of NASA's Goddard Space Flight Center told AFP.

But there may be alternate explanations for the comet's unusual chemical composition, which might not definitively prove its age, he said.

'Vast unimaginable trajectories'

The new research published in the Nature journal is based on isotopic measurements of 3I/ATLAS, which reveal an elemental composition unlike any Solar System body, according to the study's abstract.

It is based on the comet's ratio of chemical elements called isotopes detected by the James Webb Space Telescope and the ALMA observatory in Chile.

"Interstellar objects provide the only directly observable samples of icy planetesimals formed around other stars," per the study's abstract.

The comet can "therefore provide insight into the diversity of physical and chemical conditions occurring during exoplanet formation," it said.

Compared to comets in our Solar System, 3I/ATLAS has 10 times more deuterium, a type of hydrogen commonly seen in heavy water, per the study.

"That high abundance of heavy water can only really happen, according to our understanding of astrochemistry, in a very cold environment," Cordiner said.

This means the comet is also likely among the coldest objects ever seen in our Solar System, with the isotopic evidence suggesting it formed in an environment that was minus 243 degrees Celsius.

Exactly where this comet came from within the Milky Way remains a mystery.

But these interstellar objects are thought to form in a similar way to the comets in our Solar System -- flung out during the violent formation of a new planet.

As it follows an unbound, hyperbolic trajectory, 3I/ATLAS is just passing through our Solar System, and when it leaves, it will never return. Per the 3I/ATLAS tracker's mission control dashboard, it is 65% of the way through this journey.

Untethered to any star, 3I/ATLAS likely spent billions of years on "vast unimaginable trajectories around our galaxy," Cordiner said.

A rare opportunity

The scientists also detected a strange lack of chemical enrichment on the comet, which suggests it formed relatively close to stars being born.

It could even be a "relic" from an era called "cosmic noon" when many stars were forming around 10 billion years ago, Cordiner said.

The previous interstellar objects -- 1I/'Oumuamua, spotted in 2017, followed by 2I/Borisov in 2019 -- were not bright enough to gather isotopic evidence.

Several astronomers who have studied 3I/ATLAS, but were not involved in the new research, hailed the "unprecedented" results.

"Until these measurements we could only really dream about" getting this kind of information for an interstellar object, Darryl Seligman of Michigan State University told AFP.

He cautioned that the comet's age remained uncertain, adding it was "a safe bet that it's older than anything that formed in the Solar System."

Astronomer Peter Veres, who was involved in identifying the comet at the International Astronomical Union's Minor Planet Center, called the research "exciting."

"The comet is now leaving the Solar System and will never return, so future observations will become increasingly difficult," he told AFP.

However astronomers expect to spot many more interstellar objects in the coming years, particularly via the new Vera C. Rubin Observatory in Chile.

"This is just the beginning of an exciting new field, we've got a lot more to learn about these things -- and what they can tell us about our galaxy," Cordiner said.