Mineralogy and petrography of C asteroid regolith: The Sutter's Mill CM meteorite
Résumé
Based upon our characterization of three separate stones by electron and X-raybeam analyses, computed X-ray microtomography, Raman microspectrometry, and visible-IR spectrometry, Sutter’s Mill is a unique regolith breccia consisting mainly of various CMlithologies. Most samples resemble existing available CM2 chondrites, consisting ofchondrules and calcium-aluminum-rich inclusion (CAI) set within phyllosilicate-dominatedmatrix (mainly serpentine), pyrrhotite, pentlandite, tochilinite, and variable amounts of Ca-Mg-Fe carbonates. Some lithologies have witnessed sufficient thermal metamorphism totransform phyllosilicates into fine-grained olivine, tochilinite into troilite, and destroycarbonates. One finely comminuted lithology contains xenolithic materials (enstatite, Fe-Crphosphides) suggesting impact of a reduced asteroid (E or M class) onto the main Sutter’sMill parent asteroid, which was probably a C class asteroid. One can use Sutter’s Mill tohelp predict what will be found on the surfaces of C class asteroids such as Ceres and thetarget asteroids of the OSIRIS-REx and Hayabusa 2 sample return missions (which willvisit predominantly primitive asteroids). C class asteroid regolith may well contain a mixtureof hydrated and thermally dehydrated indigenous materials as well as a significantadmixture of exogenous material would be essential to the successful interpretation ofmineralogical and bulk compositional data.