Thermal evolution of the planetary bodies accreted from icy and rocky planetesimals in the early solar system

Abstract

The presented work is an extensive attempt to understand the accretion, the early thermal evolution and core-mantle differentiation of the planetary bodies accreted from icy and rocky planetesimals in the early solar system. The rocky planetary bodies include the terrestrial planets Mercury and Mars. The icy bodies include the Trans-Neptunian objects (TNOs), the minor icy planets (e.g., Ceres, Pluto, Sedan, Eris, etc.) and the icy satellites of Jupiter, Saturn, Uranus and Neptune. We have developed comprehensive numerical simulation codes, probably for the first time, considering the processes of accretion, heating, melting, core-mantle differentiation, convection, etc., inside these bodies. The decay energy of the short-lived radionuclide 26Al along with the impact-induced heating during the accretion provided sufficient heat to melt and differentiate the interior of these planetary bodies. The results indicate that the early Mars experienced widespread heating and core-mantle differentiation owing to heating by 26Al if it accreted within the initial 1.5 million years of the formation of the solar system. The results of this study are found to be consistent with the isotopic records of Martian meteorites. The numerical simulations are also performed to explain presence of large iron-core of Mercury as suggested by the recent results of MESSENGER spacecraft. The results indicate that Mercury could be a survivor of the hit and run collision with a larger planet which stripped of its mantle resulting in the formation of large iron core at the center of size ~2,000 km. The models presented for Mars and Mercury can be used to understand the thermal evolution of planetary embryos of Earth and Venus along with Mercury-like exoplanets. The thermal evolution of icy planetary bodies is also studied to explain the presence of a rocky core that is surrounded by a water ocean and an icy crust as suggested by the results of Galileo and Cassini-Huygens missions. newline