Regoliths on Small Bodies in the Solar System

Asteroid (4) Vesta: I. The howardite-eucrite-diogenite (HED) clan of meteorites

“…Considering that howardites make up roughly half of all HED polymict breccias listed in the Meteoritical Bulletin Database, the abundance of regolithic howardites may be ∼15% of HED polymict breccias. This estimate is consistent with theoretical modeling of asteroidal regoliths that shows that a packet of fragmental debris on Vesta will spend less time exposed to the space environment than the equivalent debris on the Moon (Housen and Wilkening, 1982). Warren et al (2009) noted that the few regolithic howardites identified by them tended to have a narrower range in composition than shown by the suite as a whole.…”

Siderophile and other geochemical constraints on mixing relationships among HED-meteoritic breccias

“…In part, this range in opinion arises because definitions used for regolith breccia are inconsistent and context-dependent. Regolith is often defined broadly as, e.g., ''a (surface) layer or mantle of loose, rocky material of whatever origin" (Housen and Wilkening, 1982). Lucey et al (2006, p. 84) give a similar definition, and note that every lunar rock ever acquired (at least, every non-meteoritic lunar rock) is ''from the regolith"; and thus, one might assume, any lunar breccia sample should be a regolith breccia.…”

Geologic map of the northern hemisphere of Vesta based on Dawn Framing Camera (FC) images

“…Impact cratering is the dominant process on all of these bodies, with the resulting morphologies being variable: the surface might only display bowl-shaped craters with a wide range of degradation states (e.g., Ida) or be globally affected by complex topographic structures (e.g., Lutetia) (e.g., Thomas et al, 1999Thomas et al, , 2012. As a result of impact cratering, the surfaces of planetary bodies possess a pervasive regolith on the order of 10-100 m deep, approaching 1 km for large bodies (e.g., Hausen and Wilkening, 1982). This regolith is modified and redistributed by slope processes as shown by (i) several landforms that indicate mass wasting (see Sullivan et al, 2002 for a review) and (ii) albedo features, which suggest superficial downslope motion (e.g., Thomas et al, 2002).…”