Effects of Carbon as Part of Space Weathering on Low-Albedo Asteroids

In C-complex asteroid reflectance spectra, the UV dropoff is subdued compared to the spectra of CI and CM meteorite types. The spectral absorption features identified in the VNIR of these asteroids are reduced in strength compared to laboratory spectra of terrestrial samples and meteorites. Carbon, iron sulfide, magnetite and other materials have been proposed as the darkening agent(s). Meteorites show evidence that the likely darkening agent present is iron sulfides. We also expect carbon (as graphite) to contribute to the composition of the C-complex asteroids. We note differences in the spectral properties between asteroids and meteorites at wavelengths shorter than 400 nm for asteroids whose VNIR spectra appear the same at longer wavelengths and have shown that the UV spectra can show the effects of increased carbon in the surface material. Ground-based spectra sample part of this UV spectral region, and we use this wavelength intersection to probe for additional discerning evidence of space weathering. In particular, we have shown that the effects of lunar-like (creation of SMFe) space weathering seen in the S-complex asteroids is evident in the UV/blue spectral region before it is apparent in the VNIR; this is an effect of the presence of iron in olivines. Can space weathering be the root of the differences between C-complex asteroid and CI/CM meteorite reflectance spectra? Most CM2 carbonaceous chondrites have chondrules containing ~ 20 volume % olivines; no spectrum of the chondrule contents of CM2 meteorites has been obtained.