Thermal evolution and sintering of chondritic planetesimals II. Improved treatment of the compaction process

Abstract

Reconstruction of the thermal history of individual meteorites which can be assigned to the same parent body allows to derive general characteristics of the parent body, which hold important clues on the planetary formation process. This requires to construct models for the heating of such bodies by short lived radioactives, in particular by 26Al, and its cooling by heat conduction, which then are compared with the cooling histories of the meteorites. The heat conductivity of the planetesimal material depends critically on the porosity of the chondritic material and changes by sintering of the material at elevated temperatures and pressures. Compaction of a granular material is a key process for the thermal history of the parent bodies of meteorites. The modelling of the compaction process is improved by applying concepts originally developed for hot isostatic pressing in metallurgical processes. It is extended to a binary mixture of matrix and chondrules, as observed in chondrites. By comparison with published data on sintering experiments it is shown that the algorithm allows a sufficiently accurate modelling of the compaction of silicate material. It is shown that the characteristic temperature at which sintering occurs is different for matrix or chondrule dominated precursor material. We apply the new method to model the thermal evolution of the parent body of the H chondrites and determine an improved optimized set of model parameters for this body.