The Search for Truly "Regolithic" Howardites

The howardite meteorites are polymict breccias of eucrite (basaltic) and diogenite (orthopyroxenitic) material [1] that likely originate from the asteroid 4 Vesta [2]. The true regolithic nature of the suite is not well defined, with previous research suggesting correlations between Ni and solar wind noble gas contents, and minimal variation in Al2O3 content [3]. Through combined petrological, compositional and noble gas analyses, we aim to better understand howardite petrological diversity, regolith formation processes on the parent asteroid, and to establish what defines a truly "regolithic" howardite. Our petrological study of 30 polymict eucrites and howardites has identified regolithic features (e.g. melt clasts, chondrite fragments), used to develop a regolith grading scheme. Bulk major element com-positional data have been collected [4], and both trace-element and noble gas analyses are underway. We expect those howardites with regolithic petrological and chemical features to have high abundances of implanted solar wind noble gases.