  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).
