Darkening Agents Resulting from Space Weathering on Low-Albedo Asteroids

Abstract:

Differences in the reflectance spectral properties between C-complex asteroids and CM2 carbonaceous chondrite meteorites are observed at wavelengths shorter than 400 nm for asteroids whose VNIR spectra appear the same at longer wavelengths; we observe this from comparing a limited number of space-based UV reflectance spectra of C-complex asteroids with a limited number of UV laboratory reflectance spectra. Both spectral modeling and laboratory studies have demonstrated that the UV spectra can show the effects of increased carbon in the surface material. Ground-based telescopic spectra sample part of this UV spectral region, and we use this wavelength intersection to probe for additional discerning evidence of space weathering. We present spectra of 6 C-complex asteroids, some of which overlap with the space-based UV sample. The spectra were obtained with the MMT Observatory Blue Channel spectrograph (the same instrumentation we used to obtain and study the overlap between the UV and visible spectral region for S-complex asteroids). 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, however, we also expect graphitized carbon to contribute to the composition of the C-complex asteroids. We examine both options.