غبار المذنبات: نظرة من المدار ومن المختبر سريع

الملخص الأصلي

كما كتبه المؤلفون، بالإنجليزية arXiv:2608.02190v1

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 ($$r_H$$) 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 H$$_2$$O, CH$$_4$$, C$$_2$$H$$_6$$, CH$$_3$$OH, CO, CO$$_2$$, $$^{13}$$CO$$_2$$, OCS, HCN, and CN and find molecular abundances consistent within $$2\sigma$$ with those reported during previous perihelion passages. The water ortho-to-para ratio was $$2.76\pm0.05$$, and the $$^{12}$$CO$$_2$$/$$^{13}$$CO$$_2$$ ratio was $$85\pm4$$. Thermal emission from the nucleus and dust was detected and modeled, providing an effective nucleus radius of $$1.77\pm0.04$$ km and a dust composition (relative mass fraction of the submicron grains) of $$\sim36\%$$ amorphous carbon, $$\sim25\%$$ amorphous Mg:Fe olivine, $$\sim23\%$$ Mg-rich crystalline olivine, and $$\sim15\%$$ amorphous Mg:Fe pyroxene. The crystalline mass fraction of the sub-micron grains in the coma was $$0.362\pm0.003$$. 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.