Evidence for Partial Differentiation of Carbonaceous Chondrite Planetesimals

Image credit: Aleon et al., 2020

Meteorites are categorized, in part, by differences in the degree of heating experienced by their parent bodies. Some meteorites record high degrees of heating that caused melting and differentiation of their parent bodies into layered structures with metallic cores and silicate mantles and crusts (similar to the Earth’s internal structure). On the other hand, some meteorites experienced only low degrees of heating that minimally changed their original physical-chemical nature, if at all. Many carbonaceous chondrites (CC) are of the latter types. Studying how internal heating affected meteorites and their parent bodies helps in understanding the variety of rocky bodies that were formed in the early solar system. New research led by Jérôme Aléon from the Museum National d’Histoire Naturelle (France) investigated a unique clast of trachybasaltic composition found as a xenolith in a primitive Renazzo-type carbonaceous chondrite (CR) meteorite. Based on its chemical and isotopic composition, the team determined that this clast was produced by very-low-degree partial melting of a different type of CC, a Vigarano-type (CV). The texture of this clast indicates formation within a melt ascending into a primitive chondritic crust at the onset of differentiation of the CV parent body. This study supports previous, controversial work that argued that the parent body of the CV chondrite meteorites could have been partially differentiated into a metallic core and a silicate mantle, while maintaining a relatively primitive chondritic crust. This would indicate that even “primitive” asteroids experienced dynamic internal evolution and could produce many different rock types on a single parent body. As a result, active sample-return missions, Hayabusa2 and OSIRIS-REx, to carbonaceous asteroids might return much more geologically diverse materials than originally thought. READ MORE