3I/ATLAS is an interstellar comet—the third confirmed object known to have originated beyond our solar system—and it offers a rare chance to study material from another planetary system. Early JWST observations show an unusually high carbon dioxide-to-water ratio, which may reflect the comet's origin or its high incoming speed that helped preserve volatile ices. Additional JWST and ground-based observations are planned as the comet moves away from the Sun. Many amateur astronomers may still be able to spot it with small telescopes.
Meet 3I/ATLAS: The Interstellar Comet Astronomers Are Racing to Study
3I/ATLAS is an interstellar comet—the third confirmed object known to have originated beyond our solar system—and it offers a rare chance to study material from another planetary system. Early JWST observations show an unusually high carbon dioxide-to-water ratio, which may reflect the comet's origin or its high incoming speed that helped preserve volatile ices. Additional JWST and ground-based observations are planned as the comet moves away from the Sun. Many amateur astronomers may still be able to spot it with small telescopes.
11:13 AM, 11/13/2025Science
3I/ATLAS: A Rare Visitor From Beyond Our Solar System
A comet that formed in another star system, designated 3I/ATLAS, is giving astronomers an uncommon opportunity to examine material that began its journey billions of years ago. The "I" in its name denotes an interstellar object, and the "3" marks it as the third confirmed interstellar visitor observed from Earth after 1I/ʻOumuamua and 2I/Borisov.
Discovered in 2024 by the ATLAS Survey, a worldwide network of telescopes that scans the sky for potentially hazardous asteroids and comets, 3I/ATLAS has brightened since July as it approached the Sun. Now that it has passed perihelion and is reemerging from the Sun's glare, astronomers have a fresh window to study its composition and activity.
Surprising Chemistry Detected by JWST
Soon after discovery, the James Webb Space Telescope (JWST) observed the comet and detected an unusually high ratio of carbon dioxide (CO2) to water vapor compared with typical solar-system comets. That result could reflect either the environment where 3I/ATLAS formed or how the object has evolved since ejection from its home system.
Qicheng Zhang, a postdoctoral fellow at Lowell Observatory, explained that a high CO2-to-water ratio "could be an indication of where it formed, or simply the composition of the planetary system it came from."
Another plausible explanation involves the comet's very high incoming speed. Because 3I/ATLAS raced into the inner solar system much faster than most local comets, it may have retained more volatile ices such as frozen CO2 (dry ice) that slower comets typically lose as they warm. In short, both origin and dynamical history could shape the observed chemistry.
Ongoing Observations and What to Expect
Follow-up JWST observations are planned for December, and telescopes around the world will continue to monitor how the comet's outgassing—its release of gas and dust—changes as it recedes from the Sun. These data will help scientists compare 3I/ATLAS with comets formed in our solar system and search for clues about the environments where other planetary systems form.
Researchers emphasize caution about sensational theories. While online speculation has sometimes invoked exotic explanations, scientists say there is nothing so far that requires invoking technology or non-natural causes. As Zhang put it, astronomers remain far from exhausting natural explanations.
Can You See It?
Fortunately for skywatchers, the comet is currently bright enough that many amateur astronomers can attempt a sighting with small telescopes. Observers planning to look should check up-to-date sky charts and local conditions for the best viewing windows.
Why this matters: Studying 3I/ATLAS lets scientists test whether the chemistry and formation processes that produced comets in our solar system are common elsewhere in the galaxy—or whether other systems yield markedly different kinds of icy bodies.