Comet 3I/Atlas: A Window into the Cosmic Noon - Latest Data Revealed by NASA

The James Webb Space Telescope has recently captured detailed measurements of the interstellar comet 3I/ATLAS, providing clues about its ancient and distant origins. Observations conducted in December 2025, while the comet was moving away from the Sun, revealed a chemical composition with carbon and deuterium (heavy hydrogen) ratios that differ significantly from those found in comets of our stellar system, leaving researchers puzzled.

These unexpected data, published on June 22 in the journal Nature, have allowed astronomers to reconstruct the formation environment of 3I/ATLAS. The comet, the third confirmed interstellar comet (named after the NASA-funded ATLAS telescope that first spotted it), represents a unique opportunity to study an object not originating from our Solar System.

"This has been a unique opportunity to study an ancient object from a distant galaxy, likely predating our Sun and Solar System," stated astrochemist Martin Cordiner from NASA's Goddard Space Flight Center and lead author of the study. "On one hand, we gain a direct view of that distant time and place, and on the other, we learn something about how unusual our Solar System might be."

The NASA team reveals new information about comet 3I/Atlas. The research team, with permission to stop observing Webb, used the NIRSpec (Near-Infrared Spectrograph) instrument to analyze the comet. The results showed exceptionally high levels of deuterium, about 30 times higher than those observed in Solar System comets. This implies that 3I/ATLAS may have formed in a very cold system, much earlier in our galaxy's history.

During its formation, the material incorporated into 3I/ATLAS was likely exposed to a significant amount of radiation, but not prolonged heat that would have reprocessed its "heavy water" (with deuterium) into the type of H2O ice we are familiar with on Earth. Additionally, NIRSpec detected only traces of carbon-13 compared to the lighter carbon-12. This element also indicates a very ancient origin for 3I/ATLAS, as stellar systems enrich in carbon-13 over time, as generations of stars are born and die in the galaxy. This is why in our system, around our Sun, which formed relatively recently (4.5 billion years ago), higher levels of carbon-13 are found.

Researchers estimate that 3I/ATLAS may have formed between 10 and 12 billion years ago, during the "cosmic noon" of the universe, a period of peak activity in star formation. Its young origin system was likely embedded in a relatively cold and dense cloud, with the abundance of heavy water confirming its deeply frozen state during its formative years. Further study conducted with the Very Large Telescope of the European Southern Observatory, led by astronomer Cyrielle Opitom from the University of Edinburgh, integrated Webb’s data with an analysis of carbon and nitrogen varieties, in the form of cyanide, from 3I/ATLAS.

"For us scientists, finding these rare isotopes is fascinating, but the bigger picture here is the opportunity to explore the possibilities of prebiotic chemistry elsewhere in the galaxy," commented Stefanie Milam of NASA Goddard and co-author of the study. "So far, we know of only one place in the vast cosmos where chemical ingredients have led to life - our Solar System, our Earth. Analyzing these interstellar objects is an important step in understanding how common, or uncommon, the conditions for the evolution of life are in the universe."

The James Webb Space Telescope, the world's premier scientific space observatory, continues its mission to explore the mysteries of our Solar System, distant worlds, and the origins of our universe.