Thermal evolution of planetesimals during accretion

Abstract

Although the mass distribution of planetesimals during the early stages of planetary formation has been discussed in various studies, this is not the case for their temperature distribution. Mass and temperature distributions are closely linked, since the ability of planetesimals to dissipate the heat produced by both radioactive decay and impacts is related to their size and hence mass. Here, we propose a simple model of the evolution of the joint mass-temperature distribution through a formalism that encompasses the classic statistical approach of Wetherill (1990). We compute the statistical distribution of planetesimals by using simple rules for aggregation. Although melting temperatures can be easily reached, the formation of molten planetary embryos requires that they be formed in only a few 100 kyr. Our aggregation model, which even ignores fragmentation during collision, predicts that planetesimals with radii less than approximately 20 km will not melt during their formation.