Evidence for hydrated minerals in the VNIR spectra of G-class asteroids: A first look

Abstract

We present the initial results of our visible and near-infrared (VNIR) investigation into the spectral properties of the Tholen G-class asteroids to determine: 1) which spectral properties are common among the G-class, and 2) which surface minerals may be related to the spectral features present. Our study utilized both previously published and newly obtained spectra of five G-class asteroids. Our results indicate that four of these asteroids: (13) Egeria, (19) Fortuna, (84) Klio, and (130) Elektra, exhibit spectral features consistent with hydrated minerals in the VNIR (0.4–2.5-μm). The most notable absorption feature was located at 0.7-μm, which is related to the Fe2+ ➔ Fe3+ charge transfer transition in oxidized Fe-rich phyllosilicates. In addition, several of the asteroids also exhibit subtle absorption features located near 0.95-, 1.4-, 1.9-, and 2.3-μm, which may also be related to hydrated minerals. Only (1) Ceres' spectrum lacked features related to hydrated minerals in the VNIR. This may indicate that either (1) Ceres contains lower concentrations of hydrated minerals at its surface, or that (1) Ceres has an opaque surface component, which may obscure weak hydrated VNIR features.