The Effect of Temperature-Dependent Properties on the Conductive Cooling of Planetesimals

Abstract:

Modelling the thermal evolution of planetesimals allows us to understand the geologic context of meteorite samples. The thermal evolution of these early-Solar System bodies is controlled by properties such as conductivity and volumetric heat capacity, 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 meteorite samples. We have developed a finite difference code to perform numerical simulations of a conductively cooling planetesimal with the inclusion of $T$-dependent conductivity, heat capacity and density and find that including temperature dependence produces considerable differences in thermal history, and in turn the timing and depth of formation of meteorite samples. For a representative calculation for a hypothetical 250 km radius pallasite parent body, $T$-dependent properties delay the onset of core crystallisation and the inferred period of dynamo activity by $\sim$40 Myr, approximately equivalent to increasing the planetary radius by 10\%, and extends it by $\sim$3 Myr. This affects the acceptable range of planetesimal radii and core sizes for the pallasite parent body that are compatible with paleomagnetic evidence, and cannot be reproduced by using mean constant values. In addition to the pallasite parent body or bodies, this approach also can be used to model the temperature evolution of other differentiated minor planets and primitive meteorite parent bodies and constrain the depth and timing of formation of associated meteorite samples.