Asteroid differentiation: Melting and large-scale structure

The diversity of mineralogies and textures in the asteroidal meteorite collection promises a similarly diverse array of parent bodies and relatives as we continue exploring the asteroid belt. The presence of metamorphosed and igneous meteorites demonstrates that even some small bodies were heated significantly, permitting a variety of complexly interacting processes and heterogeneities within an individual planetesimal. In particular, chondritic meteorites could even originate from the same parent body as some highly differentiated meteorites. The histories and present-day features of the asteroids depend on their initial composition and the timing and duration of the accretion process. We first discuss the energy sources driving thermal modification of planetesimals and summarize the processes involved in differentiation as hydrous, metal, and silicate melting occurs. Then we outline the aftermath of differentiation as the body cools, and close with a discussion of magnetic, geophysical, and meteoritic evidence for differentiation in planetesimals.