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Arxiv: Near to Mid-Infrared Spectroscopy of (65803) Didymos as observed by JWST: Characterization Observations Supporting the Double Asteroid Redirection Test Published: 10/17/2023 2:37:03 PM Updated: 10/17/2023 2:37:03 PM

Paper abstract: The Didymos binary asteroid was the target of the Double Asteroid RedirectionTest (DART) mission, which intentionally impacted Dimorphos, the smaller memberof the binary system. We used the Near-Infrared Spectrograph (NIRSpec) andMid-Infrared Instrument (MIRI) instruments on JWST to measure the 0.6-5 \mumand 5-20 \mum spectra of Didymos approximately two months after the DARTimpact. These observations confirm that Didymos belongs to the S asteroid classand is most consistent with LL chondrite composition as was previouslydetermined from its 0.6-2.5-\mum reflectance spectrum. Measurements atwavelengths > 2.5 \mum show Didymos to have thermal properties typical foran S-complex asteroid of its size and to be lacking absorptions deeper than~2\% due to OH or H2O. Didymos' mid-infrared emissivity spectrum is withinthe range of what has been observed on S-complex asteroids observed withSpitzer Space Telescope and is most consistent with emission from small (< 25\mum) surface particles. We conclude that the observed reflectance andphysical properties make the Didymos system a good proxy for the type ofordinary chondrite asteroids that cross near-Earth space, and a goodrepresentative of likely future impactors.