[astro-ph.EP] We report observations of comet 81P/Wild 2, target of the Stardust sample return mission, on UT 2023 March 20 and 24 at a heliocentric distance (rH) of 1.85 au using the NIRSpec and MIRI integral field unit spectrographs on board the James Webb Space Telescope (JWST).
This study is the first compositional comparison between JWST remote-sensing spectroscopy of a solar system object against terrestrial analysis of its returned samples. We securely detected molecular emission from H2O, CH4, C2H6, CH3OH, CO, CO2, 13CO2, OCS, HCN, and CN and find molecular abundances consistent within 2σ with those reported during previous perihelion passages.
The water ortho-to-para ratio was 2.76±0.05, and the 12CO2/13CO2 ratio was 85±4. Thermal emission from the nucleus and dust was detected and modeled, providing an effective nucleus radius of 1.77±0.04 km and a dust composition (relative mass fraction of the submicron grains) of ∼36% amorphous carbon, ∼25% amorphous Mg:Fe olivine, ∼23% Mg-rich crystalline olivine, and ∼15% amorphous Mg:Fe pyroxene.
The crystalline mass fraction of the sub-micron grains in the coma was 0.362±0.003. Comparison of the JWST-derived thermal model against the fine-grained materials in Stardust returned samples demonstrates complementarity between the missions, with each most sensitive to a different population of the coma dust grains.
Nathan X. Roth, Stefanie N. Milam, Diane H. Wooden, Charles E. Woodward, Dominique Bockelee-Morvan, Michael S. P. Kelley, Steven B. Charnley, Simon J. Clemett, Martin A. Cordiner, Perry A. Gerakines, David E. Harker, Els Peeters, Ella Sciamma-O’Brien, Geronimo L. Villanueva
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2608.02190 [astro-ph.EP] (or arXiv:2608.02190v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2608.02190
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Submission history
From: Nathan Roth [
[v1] Mon, 3 Aug 2026 13:14:08 UTC (5,995 KB)
https://arxiv.org/abs/2608.02190
Astrobiology, Astrogeology, Astrochemistry,
