Numerical heat transfer on highly porous aggregates and asteroid boulders

Kurzfassung

Based on its recent success, the Hayabusa2 mission (2014-2020) [1] has returned samples of C-type asteroid Ryugu (162173) to Earth, and the sample analysis is currently ongoing [2]. Remote sensing [3] and in-situ [4] data indicate an unexpectedly low thermal inertia for the majority of rocks on Ryugu [5], which has generally been attributed to a high intrinsic porosity. However, results obtained from returned samples indicate much lower porosities. The origin of this discrepancy is currently unknown and different causes, including a potential scale dependence of thermophysical properties, are being discussed [6]. While the general trend of lower thermal conductivity at high porosities seems intuitive, porosity estimates derived from thermal conductivity are currently based on an extrapolation of meteorite properties to large porosities. This is due to the fact that highly porous meteorite samples are lacking in our meteorite collections and it remains to be explored if the applied extrapolation method is physically sound. Furthermore, depending on the applied model, porosity estimates vary widely between 28% and 55% [5].