[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. Recent work determined contributions of molecular emission from coma volatiles and thermal emission from the nucleus and coma dust grains to these spectra.
Subtracting the molecular and thermal emission models produces a residual spectrum with a clear resonance near 3.37 μm and multiple others spanning the 6−12 μm region. Analysis of these residuals provides strong evidence for the presence of polycyclic aromatic hydrocarbons (PAHs) in the coma of 81P/Wild 2.
The resulting PAH populations reflect material incorporated into the nucleus of 81P/Wild 2 that was inherited from the diffuse interstellar medium, the interstellar medium, and the protoplanetary disk. The PAHs sensed by JWST are compared to those detected in laboratory analyses of the Stardust mission returned samples.
PAH Origins. Interpretive Venn diagram of the three astrophysical environments represented by the best-fit PAH model for comet 81P: the protoplanetary disk (green ellipse), the diffuse interstellar medium (DISM, blue ellipse), and the interstellar medium (ISM, purple ellipse). Each PAH structure is framed in orange (neutral PAH) or blue (PAH cation). The protoplanetary disk region contains the very small Hn-PAHs, very small and small PAHs, and C10H +2 18 (uid=4396) that is in both subpopulations of Hn-PAHs and Me-PAHs—species unlikely to survive DISM or ISM conditions. The DISM region holds the dehydrogenated PAHs (DPAHs), including C70, that form by H-loss from larger PAHs and serve as intermediates en route to fullerenes and carbon nanograins. The ISM region holds the medium and large PAHs that survive harsh PDR conditions; PANHs (skeletal N) appear among them. The DISM ellipse overlaps both flanking regions, reflecting its role as the bridge between the protoplanetary disk and the harsher environs of the ISM (see Section 4.1). — [astro-ph.EP]
Nathan X. Roth, Stefanie N. Milam, Diane H. Wooden, Els Peeters, 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, Ella Sciamma-O’Brien, Geronimo L. Villanueva
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2609.34116 [astro-ph.EP](or arXiv:2609.34116v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.34116
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Submission history
From: Nathan Roth
[v1] Mon, 28 Sep 2026 01:54:37 UTC (8,456 KB)
https://arxiv.org/abs/2609.34116
Astrobiology, Astrochemistry,
