Abstract
The differentiation of planetesimals from a loose aggregate of diverse solar nebula components into a compact and compositionally layered body consisting of core, mantle, and crust is one of the most fundamental processes in the early solar system. Differentiation involves the physical separation of metal and silicate through the segregation of dense metal melts towards the center, forming a core, and the upward migration of silicate melts, forming a crust. Direct evidence for these processes comes from differentiated meteorites as they include samples derived from the core, mantle, or crust of extensively melted bodies (McCoy et al., 2006; Mittlefehldt et al., 1998). For example, while magmatic iron meteorites formed by fractional crystallization inside a metal core (Scott, 1972; Scott and Wasson, 1975), eucrites and angrites are basaltic magmas that crystallized on or near the surface of differentiated bodies (Mittlefehldt er al., 1998). Dating such samples, therefore, makes it possible to determine the timescales of differentiation. This information is key for understanding the physical and chemical conditions of melting and melt segregation, the identification of the heat source(s) for melting, and constraining the timescales of planetesimal accretion. Obtaining such constraints is important not only for understanding the formation and evolution of planetesimals, but may also help to assess the fundamental question of why some planetesimals are differentiated while others — such as the parent bodies of chondritic meteorites — are not.
