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Thermal evolution of icy planetesimals in the solar nebula

The thermal histories and time evolutions of icy planetesimals are numerically solved with various parameters (the time of formation that corresponds to the ratio of 26Al/27Al, the size of the planetesimals and their initial temperature). We consider the formation of a rocky core due to the settling of rocks after the melting of ice. We also take into account two chemical reactions, aqueous alteration and a dehydration reaction, between rocks and water. Results of numerical simulations show that a key factor is the initial ratio of 26Al/27Al. Our results indicate that icy planetesimals, formed at 2.4 Myr after CAI formation, may not reach the melting temperature of ice, regardless of their sizes and initial temperature.