Thermal model of Mercury’s surface and subsurface: Impact of subsurface physical heterogeneities on the surface temperature

Abstract

The surface temperature of Mercury will be monitored by the IR radiometer on board the MPO orbiter of the BepiColombo mission. These results are expected to provide information about regolith thermal and thermo-optical properties at the surface, but also in the near subsurface. The presence of physical heterogeneities, resulting in discontinuities of the vertical profiles of subsurface physical parameters (like thermal conductivity, heat capacity, porosity, etc.) is expected to imprint its signature on the time evolution of surface temperature, in particular at twilight, when the temperature does rapidly vary, and during the night. It might as well affect the absolute level of surface temperature, on both dayside and nightside, due to possible horizontal variations of thermal inertia, because of topography and/or geographical variations of regolith textural properties. We have therefore developed a thermal model of Mercury’s regolith which includes radiative and conductive effects, and tests the effect of various subsurface inhomogeneities on the observed temperature curves. Such a model describes the diurnal variation of the surface temperature and of the temperature profile in the first meters below the surface. This model has been tested with respect to known measurements of Mercury’s surface temperature [Chase, S.C., Miner, Jr., E.D., Morrison, D. et al. Mariner 10 infrared radiometer results: temperatures and thermal properties of the surface of Mercury. Icarus 28, 655–578, 1976] and previous existing models [Hale, A.S., Hapke, B. A time-dependent model of radiative and conductive thermal energy transport in planetary regoliths with applications to the Moon and Mercury. Icarus 156, 318–334, 2002].