JWST Detection of a Carbon-dioxide-dominated Gas Coma Surrounding Interstellar Object 3I/ATLAS
Year: 2025
Type: article
Abstract: 3I/ATLAS is the third confirmed interstellar object to visit our solar system and only the second to display a clear coma. Infrared spectroscopy with the James Webb Space Telescope (JWST) provides the opportunity to measure its coma composition and determine the primary activity drivers. We report the first results from our JWST NIRSpec campaign for 3I/ATLAS, at an inbound heliocentric distance of r H = 3.32 au. The spectral images (spanning 0.6–5.3 μ m) reveal a CO 2 -dominated coma, with enhanced outgassing in the sunward direction and the presence of H 2 O, CO, water ice, dust, and a tentative detection of OCS. The coma CO 2 /H 2 O mixing ratio of 7.6 ± 0.3 is among the highest ever observed in a comet, and is 4.5 σ above the trend as a function of r H for long-period and Jupiter-family comets (excluding the outlier C/2016 R2). Our observations are compatible with an intrinsically CO 2 -rich nucleus, which may indicate that 3I/ATLAS contains ices exposed to higher levels of radiation than solar system comets or that it formed close to the CO 2 ice line in its parent protoplanetary disk. A relatively low coma H 2 O gas abundance may also be implied, for example, due to inhibited heat penetration into the nucleus, which could suppress the H 2 O sublimation rate relative to CO 2 and CO.
Institutions: Goddard Space Flight Center, Catholic University of America, American University, University of Maryland, College Park, Auburn University, Physikalisch-Meteorologisches Observatorium Davos, Jet Propulsion Laboratory, European Space Agency, Royal Observatory, University of Edinburgh, Queen's University Belfast, Northern Arizona University, Armagh Observatory & Planetarium
Language: English
Topic: Astro and Planetary Science
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,400
OpenAlex ID: W4414531245