Coma Physics of an Interstellar Object: JWST Spatial-Spectral Mapping of 3I/ATLAS
Nathan X. Roth, Martin A. Cordiner, Stefanie N. Milam, Geronimo L. Villanueva, Steven B. Charnley, Nicolas Biver, Dominique Bockelee-Morvan, Dennis Bodewits, Steven J. Bromley, Jacques Crovisier, Maria N. Drozdovskaya, Sara Faggi, Davide Farnocchia, Kenji Furuya

TL;DR
This study used JWST to map molecular emissions from interstellar object 3I/ATLAS, revealing volatile distributions, anisotropic coma properties, and insights into its nucleus composition and thermal processes.
Contribution
First spatial-spectral mapping of multiple volatiles in an interstellar object’s coma, showing volatile segregation and coma heating mechanisms.
Findings
CO was the most abundant molecule in 3I/ATLAS.
Spatial distributions of molecules were highly anisotropic for apolar species.
H2O ortho-to-para ratio was flat and slightly below equilibrium.
Abstract
We report a survey of molecular emission from cometary volatiles using the James Webb Space Telescope (JWST) toward interstellar object 3I/ATLAS carried out on UT 2025 December 22 and 23 at a heliocentric distance () of au. These measurements of CO, CO, HO, CHOH, and CH sampled molecular chemistry in 3I/ATLAS as it receded from its encounter with our Sun and entered the vicinity of the HO ice line -- the region between = au where the temperature becomes too low for HO to vigorously sublime and CO and CO begin to control the overall activity. CO was the most abundant molecule, followed by HO and CO, whose molecular abundances with respect to CO were and (, respectively. This work presents spatial-spectral maps of column density and rotational temperature as a function of distance from the…
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