Thermal evolution and sintering of chondritic planetesimals

Abstract

The major aim of this study is to assess the effects of sintering of initially porous material on the thermal evolution of planetesimals, and to constrain the values of basic parameters that determined the structure and evolution of the H chondrite parent body. A new code is presented for modeling the thermal evolution of ordinary chondrite parent bodies that initially are highly porous and undergo sintering by hot pressing as they are heated by decay of radioactive nuclei. The pressure and temperature stratification in the interior of the bodies is calculated by solving the equations of hydrostatic equilibrium and energy transport. The decrease of porosity of the granular material by hot pressing due to self-gravity is followed by solving a set of equations for the sintering of powder materials. For the heat conductivity of granular material we combine recently measured data for highly porous powder materials, relevant for the surface layers of planetesimals, with data for heat conductivity of chondrite material, relevant for the strongly sintered material in deeper layers. To demonstrate the capability of our new model, the thermal evolution of the H chondrite parent body was reconstructed. The model starts with a porous body that is later compacted first by 'cold pressing' at low temperatures and then by 'hot pressing' for temperatures above \approx 700 K, i.e., the threshold temperature for sintering of silicates. The thermal model was fitted to the well constrained cooling histories of the two H chondrites Kernouve (H6) and Richardton (H5).