The Astrophysical Journal Letters (Jan 2024)

Detection of a 2.85 μm Feature on Five Spinel-rich Asteroids from JWST

  • Jonathan Gomez Barrientos,
  • Katherine de Kleer,
  • Bethany L. Ehlmann,
  • Francois L. H. Tissot,
  • Jessica Mueller

DOI
https://doi.org/10.3847/2041-8213/ad4647
Journal volume & issue
Vol. 967, no. 1
p. L11

Abstract

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Ground-based observations of “Barbarian” L-type asteroids at 1–2.5 μ m indicate 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 during the formation of the solar system. However, the spectral properties of these asteroids from 2.5–5 μ m, a wavelength region that covers signatures of hydrated minerals, water, and organics, have not yet been explored. Here, we present 2–5 μ m reflectance spectra of five spinel-rich asteroids obtained with the NIRSpec instrument on the James Webb Space Telescope. All five targets exhibit a ∼2.85 μ m absorption feature with a band depth of 3%–6% that appears correlated in strength with that of the 2 μ m spinel absorption feature. The shape and position of the 2.85 μ m feature are not a good match to the 2.7 μ m feature commonly seen in carbonaceous CM meteorites or C-type asteroids. The closest spectral matches are to the Moon and Vesta, suggesting commonalities in aqueous alteration across silicate bodies, infall of hydrated material, and/or space weathering by solar wind H implantation. Lab spectra of CO/CV chondrites, CAIs, as well as the minerals cronstedtite and spinel, also show a similar feature, providing clues into the origin of the 2.85 μ m feature.

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