Interstellar comet 3I/ATLAS exhibits a unique chemical signature, distinguishing it from comets in our solar system, and may have originated 10 to 12 billion years ago—predating the Sun itself—according to two studies published in the journal Nature.
Hubble captured this stunning image of 3I/ATLAS on July 21, 2025. At this time, the comet was located 446 million kilometers (277 million miles) from Earth. Image credits: NASA/ESA/David Jewitt, UCLA/Joseph DePasquale, STScI.
Discovered in July 2025, 3I/ATLAS is the third known interstellar object to enter the inner solar system.
Despite extensive observations, the precise age, origin, and trajectory of 3I/ATLAS remain uncertain.
Estimates based on its speed suggest an age ranging from 3 billion to 10 billion years old.
Analyzing isotope ratios offers insights into the physical and chemical conditions present during the formation of 3I/ATLAS.
“This presents a rare opportunity to study an ancient celestial body, possibly older than the Sun or our Solar System,” said Dr. Martin Cordiner, an astronomer at NASA’s Goddard Space Flight Center.
“On one hand, we gain direct insight into distant epochs and locations; on the other, we learn more about the unique nature of our solar system.”
As 3I/ATLAS moved away from the Sun in December 2025, Cordiner and colleagues utilized the NASA/ESA/CSA James Webb Space Telescope to acquire detailed measurements of its chemical makeup.
Webb’s NIRSpec (Near Infrared Spectrometer) revealed exceptionally high deuterium levels—approximately 30 times greater than those found in solar system comets.
This indicates that 3I/ATLAS may have originated in the earlier phases of the Milky Way, within a very cold star system.
During its formation, the material inside the comet was likely subjected to substantial radiation exposure, but not warm enough for an extended duration to transform its heavy water ice into the type of ice familiar on Earth.
Moreover, NIRSpec detected only minute amounts of carbon-13 compared to the lighter carbon-12, reinforcing the notion of 3I/ATLAS’s ancient origin.
In contrast, planetary systems formed around the Sun, about 4.5 billion years ago, show higher levels of carbon-13.
The authors estimate that 3I/ATLAS formed approximately 10 to 12 billion years ago during the “cosmic noon” of the universe—when star formation peaked.
In its early days, the system may have been enveloped in a relatively cool, dense cloud.
The elevated levels of heavy water indicate that 3I/ATLAS spent its formative years in a state of deep freeze.
This infographic illustrates the stark differences in heavy carbon to deuterium ratios between solar system comets and the 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 utilizing the UV-Visual Echelle Spectrometer (UVES) of ESO’s Very Large Telescope from December 6 to 26, 2025.
Their findings complement those from Webb by analyzing the chemical forms of carbon and nitrogen present in 3I/ATLAS.
“While the discovery of these rare isotopes intrigues us as scientists, the broader significance lies in exploring the potential for prebiotic chemistry elsewhere in the galaxy,” noted Dr. Stephanie Milam, also from NASA’s Goddard Space Flight Center.
“Currently, we only know one location in the vast universe where chemical components have led to life: our solar system and Earth.”
“Examining these interstellar objects is a pivotal step toward understanding how common or rare conditions for life’s evolution may be across 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 ratios of nitrogen and carbon in interstellar comet 3I/ATLAS. Nature, in press. arXiv: 2603.07187
Source: www.sci.news
