Coma Physics of an Interstellar Object: JWST Spatial–Spectral Mapping of 3I/ATLAS
14 affiliations
- 1American University
- 2NASA Goddard Space Flight Center
- 3The Catholic University of America
- 4Sorbonne Université
- 5Auburn University
- 6Physikalisch-Meteorologisches Observatorium Davos und Weltstrahlungszentrum (PMOD/WRC)
- 7Universität Bern
- 8California Institute of Technology
- 9Pioneering Research Institute
- 10University of Maryland
- 11ESA NEO Coordination Centre
- 12University of Edinburgh
- 13Queen’s University Belfast
- 14Northern Arizona University
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 ( r H ) of 2.37–2.41 au. These measurements of CO, CO 2 , H 2 O, CH 3 OH, and CH 4 sampled molecular chemistry in 3I/ATLAS as it receded from its encounter with our Sun and entered the vicinity of the H 2 O ice line—the region between r H = 2 and 3 au where the temperature becomes too low for H 2 O to vigorously sublime, and CO and CO 2 begin to control the overall activity. CO was the most abundant molecule, followed by H 2 O and CO 2 , whose molecular abundances with respect to CO were (40.5 ± 3.1)% and (41.6 ± 0.3)%, respectively. This work presents spatial–spectral maps of column density and rotational temperature as a function of distance from the nucleus for all detected species. The spatial distributions of both quantities were highly anisotropic for the apolar species in the coma of 3I/ATLAS, yet were more nearly symmetric for the polar molecules. These results demonstrate how volatiles were segregated in the nucleus ices of 3I/ATLAS and reveal heating and cooling mechanisms in its coma. Derived maps of the ortho-to-para ratio (OPR) for H 2 O were flat with increasing distance from the nucleus and consistent with a coma-averaged value OPR = 2.7 ± 0.2, slightly less than the expected equilibrium value of 3.
Related
- Mapping of interstellar ices with JWST in protostellar envelopes: Spatial variations of 13CO2, 12CO2, CO, OCN- and H2O ice
- An enriched methane D/H ratio in the interstellar object 3I/ATLAS
- Interstellar Object 3I/ATLAS Observed from Mars by China’s Tianwen-1 Spacecraft
- High water D/H ratio of the interstellar object 3I/ATLAS is consistent with a low-metallicity origin
- R(V) parameter of the dust extinction curve: Mapping based on hot stars and connections to diffuse interstellar bands
BibTeX
@article{roth2026coma,
title = {{Coma Physics of an Interstellar Object: JWST Spatial–Spectral Mapping of 3I/ATLAS}},
author = {Nathan X. Roth and Martin Cordiner and Stefanie N. Milam and Geronimo Luis Villanueva and Steven B. Charnley and N. Biver and Dominique Bockelée-Morvan and Dennis Bodewits and Steven Bromley and J. Crovisier and M. N. Drozdovskaya and Sara Faggi and Davide Farnocchia and Kenji Furuya and Michael S. P. Kelley and M. Micheli and John W. Noonan and Cyrielle Opitom and Megan E. Schwamb and Cristina A. Thomas},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = jun,
doi = {10.3847/2041-8213/ae7443},
url = {https://doi.org/10.3847/2041-8213/ae7443},
note = {CC BY},
}
RIS
TY - JOUR
TI - Coma Physics of an Interstellar Object: JWST Spatial–Spectral Mapping of 3I/ATLAS
AU - Nathan X. Roth
AU - Martin Cordiner
AU - Stefanie N. Milam
AU - Geronimo Luis Villanueva
AU - Steven B. Charnley
AU - N. Biver
AU - Dominique Bockelée-Morvan
AU - Dennis Bodewits
AU - Steven Bromley
AU - J. Crovisier
AU - M. N. Drozdovskaya
AU - Sara Faggi
AU - Davide Farnocchia
AU - Kenji Furuya
AU - Michael S. P. Kelley
AU - M. Micheli
AU - John W. Noonan
AU - Cyrielle Opitom
AU - Megan E. Schwamb
AU - Cristina A. Thomas
PY - 2026
DA - 2026/06/24
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/ae7443
UR - https://doi.org/10.3847/2041-8213/ae7443
AB - 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 ( r H ) of 2.37–2.41 au. These measurements of CO, CO 2 , H 2 O, CH 3 OH, and CH 4 sampled molecular chemistry in 3I/ATLAS as it receded from its encounter with our Sun and entered the vicinity of the H 2 O ice line—the region between r H = 2 and 3 au where the temperature becomes too low for H 2 O to vigorously sublime, and CO and CO 2 begin to control the overall activity. CO was the most abundant molecule, followed by H 2 O and CO 2 , whose molecular abundances with respect to CO were (40.5 ± 3.1)% and (41.6 ± 0.3)%, respectively. This work presents spatial–spectral maps of column density and rotational temperature as a function of distance from the nucleus for all detected species. The spatial distributions of both quantities were highly anisotropic for the apolar species in the coma of 3I/ATLAS, yet were more nearly symmetric for the polar molecules. These results demonstrate how volatiles were segregated in the nucleus ices of 3I/ATLAS and reveal heating and cooling mechanisms in its coma. Derived maps of the ortho-to-para ratio (OPR) for H 2 O were flat with increasing distance from the nucleus and consistent with a coma-averaged value OPR = 2.7 ± 0.2, slightly less than the expected equilibrium value of 3.
SN - 2041-8205
SN - 2041-8213
ER -