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Measuring the Polycyclic Aromatic Hydrocarbon Content of Comets with JWST: Comet 81P/Wild 2 and Links to Stardust

Presentation #400.01 in the session Comets: Coma (Oral Presentation)

Published onOct 23, 2023
Measuring the Polycyclic Aromatic Hydrocarbon Content of Comets with JWST: Comet 81P/Wild 2 and Links to Stardust

Comets are primitive remnants of solar system formation, cryogenically preserved in the outer solar system for the last 4.5 Gyr and retaining a record of the volatile and refractory material incorporated into their nuclei from the protosolar disk. Remote sensing of cometary atmospheres provides a window into the volatile and refractory species preserved in their nuclei from the cold protoplanetary disk midplane (the comet formation region).

Comet 81P/Wild 2 is a Jupiter-family comet and was the target of the Stardust sample return mission. The returned samples provided an unprecedented window into the composition of cometary refractory materials. They revealed a complex mixture of aromatic and aliphatic compounds similar to that found in interplanetary dust particles and meteorites, along with enrichments in deuterium and heavy nitrogen consistent with a primordial heritage. Conversely, the detection of crystalline silicates in the samples indicated significant radial mixing in the protoplanetary disk and a complex formation scenario for cometary nuclei. A favorable observing geometry several years following the Stardust encounter enabled ground-based characterization of H2O and several trace volatiles, but mid-infrared spectroscopy remained difficult.

The James Webb Space Telescope (JWST) observed comet 81P/Wild 2 on 2023 March 20 and 24 with the MIRI MRS and NIRSpec IFU instruments near rH = 1.8 au and D = 1.4 au, providing high resolution (R ~ 2,700) spectral imaging with continuous coverage from 2.9 – 28 μm.

We will discuss preliminary results from our JWST Cycle 1 GO program targeting 81P/Wild 2, providing a comprehensive volatile inventory and an analysis of solid-state features associated with coma dust. Strong molecular emission from a suite of volatiles has been identified, and we will provide molecular production rates, rotational temperatures, and isotopic ratios. The mid-infrared continuum presents a rich spectrum indicative of silicate dust grains in the coma.

Analysis of these data will enable characterization of the volatile and refractory components of the coma of 81P/Wild 2 with unprecedented sensitivity and spectral coverage, revealing material unaffected by sample capture and enabling the first comparison with the Stardust returned samples. These cometary spectra will be compared with those of extrasolar sources (e.g., the interstellar medium, evolved stars) to investigate the heritage of volatile and refractory material preserved in 81P/Wild 2 and to discern the extent to which cometary material is preserved from the interstellar medium vs. processed nebular material.

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