Interstellar comet defies expectations with unprecedented chemistry

Friday 05 September 2025 - 16:00

By: Dakir Madiha

Interstellar comet defies expectations with unprecedented chemistry

The interstellar comet 3I/ATLAS, the third confirmed visitor from beyond our solar system, has astonished scientists with its unusually high levels of carbon dioxide and unexpected activity as it approaches the Sun. Multiple NASA missions and international observatories are closely studying its composition ahead of its closest solar encounter next month.

A groundbreaking carbon dioxide discovery

On August 6, NASA’s James Webb Space Telescope (JWST) captured detailed observations of 3I/ATLAS, revealing the most carbon dioxide-rich coma ever recorded in a comet. According to Martin Cordiner of NASA’s Goddard Space Flight Center, the CO2-to-water ratio measured at 8-to-1 is the highest ever observed, surpassing typical values by six standard deviations.

“This extraordinary CO2-to-water ratio suggests the comet either formed near the carbon dioxide ice line of its parent protoplanetary disk or contains ice layers exposed to higher radiation levels than solar system comets,” explained Cordiner.

In addition to detecting carbon dioxide, JWST identified water, carbon monoxide, carbonyl sulfide, and dust in the comet's coma. The carbon monoxide-to-water ratio, however, appeared more typical at 1.4. ESA astronomer Marco Micheli noted the technical challenges of capturing the comet, emphasizing the precision required.

A growing tail signals increased activity

On August 27, the Gemini South Telescope in Chile captured the most detailed images yet of 3I/ATLAS, showing a dramatically expanded coma and tail. The tail now spans about 1/120th of a degree in the sky, pointing away from the Sun.

“This level of activity suggests the comet is becoming more dynamic as it moves deeper into the inner solar system,” reported NOIRLab, the National Science Foundation’s observatory operator.

Led by astronomer Karen Meech of the University of Hawaii, the observations also involved students who participated in real-time data collection. Meech highlighted the scientific goals, stating, “We aimed to study the comet’s colors to understand the composition and size of its dust particles, as well as capture spectra for direct chemical analysis.”

Mysterious metallic signatures

Adding to its uniqueness, the European Southern Observatory’s Very Large Telescope detected significant nickel vapor emissions from the comet but found no traces of iron. Astronomer Thomas Puzia, whose team analyzed the data, described this as unprecedented: “This opens the door to an entirely new realm of comet chemistry we’ve never encountered before.”

The absence of iron alongside nickel suggests unknown chemical processes shaped by the comet’s interstellar journey over billions of years.

Racing toward perihelion

Discovered on July 1 by the NASA-funded ATLAS survey in Chile, 3I/ATLAS is currently traveling at approximately 210,000 kilometers per hour. The comet will reach its closest approach to the Sun, at a distance of 1.4 astronomical units, on October 29. It poses no threat to Earth, with its closest approach maintaining a safe distance of 269 million kilometers in December.

As only the third confirmed interstellar object after 'Oumuamua in 2017 and 2I/Borisov in 2019, 3I/ATLAS offers scientists a unique chance to study material formed around a distant star. Its hyperbolic trajectory will eventually return it to interstellar space, making current observations a once-in-a-lifetime opportunity.

Though its visibility from Earth will diminish during perihelion due to the Sun’s glare, the comet is expected to reappear in November for further observations.