A JWST Study of Stardust. II. Polycyclic Aromatic Hydrocarbons in Comet 81P/Wild 2 and Implications for Primitive Solar System Carbon

JWST observed comet 81P/Wild 2, the target of the Stardust sample return mission, on UT 2023 March 20 and 24 at a heliocentric distance of 1.85 au using the NIRSpec and MIRI integral field unit spectrographs. The study is described as the first compositional comparison between JWST remote-sensing spectroscopy of a solar system object and terrestrial analysis of that object's returned samples.

Recent work determined the 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 other features spanning the 6–12 μm region.

Analysis of these residuals provides strong evidence for polycyclic aromatic hydrocarbons (PAHs) in the coma of 81P/Wild 2. The resulting PAH populations reflect material incorporated into the comet's nucleus that was inherited from the diffuse interstellar medium, the interstellar medium, and the protoplanetary disk. The PAHs sensed by JWST are then compared to those detected in laboratory analyses of the Stardust mission returned samples.