Evidence of space weathering in regolith breccias I: Lunar regolith breccias

Abstract

We have analyzed a suite of lunar regolith breccias in order to assess how well space weathering products can be preserved through the lithification process and therefore whether or not it is appropriate to search for space weathering products in asteroidal regolith breccia meteorites. It was found that space weathering products, vapor/sputter deposited nanophase-iron-bearing rims in particular, are easily identified in even heavily shocked/compacted lunar regolith breccias. Such rims, if created on asteroids, should thus be preserved in asteroidal regolith breccia meteorites. Two additional rim types, glass rims and vesicular rims, identified in regolith breccias, are also described. These rims are common in lunar regolith breccias but rare to absent in lunar soils, which suggests that they are created in the breccia-forming process itself. While not "space weathering products" in the strictest sense, these additional rims give us insight into the regolith breccia formation process. The presence or absence of glass and/or vesicular rims in asteroidal regolith breccias will likewise tell us about environmental conditions on the surface of the asteroid body on which the breccia was created.