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Arxiv: Detection of a 2.85 micrometer Feature on 5 Spinel-rich Asteroids from JWST Published: 5/20/2024 9:00:01 PM Updated: 5/20/2024 9:00:01 PM

Paper abstract: Ground-based observations of `Barbarian' L-type asteroids at 1 to 2.5-\mumindicate that their near-infrared spectra are dominated by the mineral spinel,which has been attributed to a high abundance of calcium-aluminum inclusions(CAIs) -- the first solids to condense out of the protoplanetary disk duringthe formation of the Solar System. However, the spectral properties of theseasteroids from 2.5 to 5-\mum, a wavelength region that covers signatures ofhydrated minerals, water, and organics, have not yet been explored. Here, wepresent 2 to 5-\mum reflectance spectra of five spinel-rich asteroidsobtained with the NIRSpec instrument on the James Webb Space Telescope. Allfive targets exhibit a ~ 2.85-\mum absorption feature with a band depthof 3-6\% that appears correlated in strength with that of the 2-\mum spinelabsorption feature. The shape and position of the 2.85-\mum feature are not agood match to the 2.7-\mum feature commonly seen in carbonaceous CMmeteorites or C-type asteroids. The closest spectral matches are to the Moonand Vesta, suggesting commonalities in aqueous alteration across silicatebodies, infall of hydrated material, and/or space weathering by solar wind Himplantation. Lab spectra of CO/CV chondrites, CAIs, as well as the mineralscronstedtite and spinel, also show a similar feature, providing clues into theorigin of the 2.85-\mum feature.