Interstellar comet 3I/ATLAS exhibits a unique chemical signature distinct from comets in our solar system and is believed to have formed 10 to 12 billion years ago, predating the Sun, according to two studies published in the journal Nature.
Hubble captured this image of 3I/ATLAS on July 21, 2025. At that time, the comet was 446 million kilometers (277 million miles) from Earth. Image credits: NASA/ESA/David Jewitt, UCLA/Joseph DePasquale, STScI.
Discovered in July 2025, 3I/ATLAS represents the third confirmed interstellar object to traverse the inner solar system.
Despite extensive observations, the precise age, origin, and trajectory of 3I/ATLAS remain elusive.
Its speed suggests an age estimate ranging from 3 billion to 10 billion years.
Analyzing isotope ratios offers insights into the environmental conditions during the formation of 3I/ATLAS.
“This was a once-in-a-lifetime opportunity to investigate an ancient celestial object, possibly older than our Sun or the solar system itself,” stated Dr. Martin Cordiner, an astronomer at NASA’s Goddard Space Flight Center.
“We gain direct insights into distant epochs and locales, while also appreciating the uniqueness of our solar system.”
As 3I/ATLAS started its journey away from the Sun in December 2025, Cordiner and his team utilized NASA/ESA/CSA’s James Webb Space Telescope to gather detailed measurements of its chemical composition.
Webb’s NIRSpec (near-infrared spectrometer) revealed exceptionally high levels of deuterium, approximately 30 times greater than that found in solar system comets.
This suggests that 3I/ATLAS may have originated during an earlier era in Milky Way history, likely in a frigid star system.
During its formation, the materials within 3I/ATLAS were likely subjected to substantial radiation, yet not warm enough to transform heavy water ice into the familiar form of water ice found on Earth.
Additionally, NIRSpec identified only minimal amounts of carbon-13 relative to lighter carbon-12, indicating an ancient origin for 3I/ATLAS.
In contrast, higher carbon-13 levels are found in planetary systems around the Sun that formed more recently, a mere 4.5 billion years ago.
Researchers propose that 3I/ATLAS formed between 10 and 12 billion years ago, at the “cosmic noon” of the universe’s history, a period marked by peak star formation.
Its youthful formation might have occurred within a relatively cool, dense cloud.
The high concentration of heavy water suggests that 3I/ATLAS spent its formative years in a deeply frozen state.
This infographic illustrates the differences in heavy carbon to deuterium ratios between solar system comets and interstellar comet 3I/ATLAS. Image credit: NASA / ESA / CSA / M. Cordiner / L. Hustak, STScI.
In a related study, astronomer Cyriel Opitum from the University of Edinburgh and colleagues conducted observations of interstellar visitors using the UV-Visual Echelle Spectrometer (UVES) at ESO’s Very Large Telescope from December 6 to 26, 2025.
Their findings complement Webb’s results by analyzing the chemical forms of carbon and nitrogen in 3I/ATLAS.
“While the discovery of these rare isotopes is exciting for us as scientists, the broader purpose is to explore the potential for prebiotic chemistry in other parts of the galaxy,” noted Dr. Stephanie Milam, also of NASA’s Goddard Space Flight Center.
“Currently, Earth is the only known location in the vast universe where chemical components have led to life.”
“Studying these interstellar objects is a significant step toward understanding how common or rare the conditions for life’s evolution are in the universe.”
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M. Cordiner et al. Isotopic evidence for the cold and distant origin of 3I/ATLAS. Nature published online June 22, 2026. doi: 10.1038/s41586-026-10771-6
C. Opitom et al. 2026. High isotopic ratio of nitrogen and carbon in interstellar comet 3I/ATLAS. Nature in press. arXiv: 2603.07187
Source: www.sci.news