Abstract
Modelling the planetary heat transport of small bodies in the early
Solar System allows us to understand the geological context of meteorite
samples. Conductive cooling in planetesimals is controlled by thermal
conductivity, heat capacity, and density, which are functions of
temperature (T). We investigate if the incorporation of the T-dependence
of thermal properties and the introduction of a non-linear term to the
heat equation could result in different interpretations of the origin of
different classes of meteorites. We have developed a finite difference
code to perform numerical models of a conductively cooling planetesimal
with T-dependent properties and find that including T-dependence
produces considerable differences in thermal history, and in turn the
estimated timing and depth of meteorite genesis. We interrogate the
effects of varying the input parameters to this model and explore the
non-linear T-dependence of conductivity with simple linear functions.
Then we apply non-monotonic functions for conductivity, heat capacity
and density fitted to published experimental data. For a representative
calculation of a 250 km radius pallasite parent body, T-dependent
properties delay the onset of core crystallisation and dynamo activity
by ~40 Myr, approximately equivalent to increasing the
planetary radius by 10 %, and extend core crystallisation by
~3 Myr. This affects the range of planetesimal radii and
core sizes for the pallasite parent body that are compatible with
paleomagnetic evidence. This approach can also be used to model the
T-evolution of other differentiated minor planets and primitive
meteorite parent bodies and constrain the formation of associated
meteorite samples.