PLANETESIMAL FORMATION BY SUBLIMATION

This paper proposes a scenario for the formation of rocky plantesimals. In this scenario, the infall of an icy dust aggregate to the central star occurs because of gas drag in the protoplanetary nebula. The temperature of the aggregate rises and H2O ice sublimates within the snow line. The silicate cores in a dust grain are ejected, following which sublimation occurs. Because the infall velocity of a silicate grain is much less than that of the original aggregate, the silicate cores stagnate in the sublimation region. We calculate the evolution of the dust surface density distribution of the silicate cores. It is shown that the surface density is increased by a factor of 10 or more, which is sufficient to trigger gravitational instability in ∼600 yr after the formation of ∼10 cm sized aggregates.