Scientists have uncovered extraordinary new details about 3I/ATLAS, a rare interstellar comet that entered the Solar System from another star system, providing scientists with a unique opportunity to study material formed billions of years before the Sun and planets came into existence.
According to NASA, researchers used the James Webb Space Telescope to investigate the comet after it made its closest approach to the Sun in December 2025.
As the comet moved away from the Sun, its ancient ice began to vaporize, forming a bright gas cloud around it. This process made it possible for astronomers to analyze its chemical composition in unprecedented detail.
The findings, published on June 22 in the journal Nature, revealed chemical characteristics unlike those found in any known comet originating within the Solar System.
Chemical Analysis Using Webb's NIRSpec
Scientists examined the object using Webb's Near-Infrared Spectrograph (NIRSpec), which enabled them to measure key chemical ratios, including carbon isotopes and deuterium, a heavier form of hydrogen often referred to as "heavy hydrogen."
One of the study's most surprising discoveries was the exceptionally high abundance of deuterium. Researchers found that 3I/ATLAS contains about 30 times as much deuterium as comets in the Solar System. This unusually high concentration suggests the comet formed in an extremely cold environment early in the galaxy's history.
Scientists believe the material that eventually became part of the comet was exposed to significant levels of radiation during its formation.
However, it remained frozen for billions of years. It avoided the prolonged warming that typically alters heavy water ice into the form commonly found on Earth and elsewhere in the Solar System.
Carbon Isotope Ratios
The James Webb observations also revealed unusually low levels of carbon-13 compared to carbon-12. Researchers say this ratio provides another important clue about the comet's age.
Over time, successive generations of stars enrich galaxies with carbon-13 through stellar evolution and supernova explosions. Since the Solar System formed relatively recently, around 4.5 billion years ago, it contains higher levels of carbon-13. The low carbon-13 content observed in 3I/ATLAS indicates that the comet likely originated much earlier in the Milky Way's history.
About 3I/ATLAS
The comet is named for being the third confirmed interstellar comet ever discovered. At the same time, "ATLAS" refers to the NASA-funded Asteroid Terrestrial-impact Last Alert System telescope that first detected it.
The research was led by astrochemist Martin Cordiner of NASA's Goddard Space Flight Centre. Cordiner described the comet as a rare scientific treasure that offers direct insight into a distant region of the galaxy and a period that predates the formation of the Sun and the Solar System.
According to him, studying the object helps scientists understand not only how other planetary systems formed but also how unusual or typical our own Solar System may be.
The Research Process
To examine the comet, Cordiner and his team collaborated with astronomers from multiple disciplines. The researchers received special approval to interrupt previously scheduled observations on the James Webb Space Telescope so they could study 3I/ATLAS during its passage through the Solar System.
Origins and Age of the Comet
Based on the comet's chemical makeup, the team estimates that 3I/ATLAS formed between 10 billion and 12 billion years ago. This would place its origin during the universe's "Cosmic Noon," a period when star formation across galaxies was occurring at its highest rate.
Scientists believe the comet originated within a cold, dense molecular cloud in a distant stellar system. The large quantity of heavy water preserved within the object suggests it spent its early history in an extremely frozen state before eventually being ejected into interstellar space.
Researchers say the discovery provides one of the clearest opportunities yet to study ancient material from beyond the Solar System. The findings could improve our understanding of how stars, planets, and planetary systems evolved throughout the galaxy's history and offer a rare glimpse into conditions that existed billions of years before Earth formed.
