The thermal inertia of the surface of Mars

Abstract

ABSTRACT The thermal inertia of Mars is a physical property that controls the diurnal and seasonal cycles in surface temperature. It is defined as a function of the thermal conductivity, heat capacity, and density, all of which depend primarily on the physical structure of the surface layer. As such, thermal inertia provides information about the nature of the surface of Mars and the types of materials from which it is composed. Interpreting thermal inertia can be complicated by the variety of structures and material properties that result in the same thermal inertia value. In general, variations in the thermal conductivity have the greatest influence on the thermal inertia. Factors such as soil grain size, cementing or induration, rock abundance, the presence of bedrock, and surface heterogeneity all play an important role. The physical processes that effect the thermal conductivity are discussed to provide a framework from which thermal inertia of the Martian surface may be better understood. Over the years, thermal inertia has been derived from numerous Earth-based and spacecraft temperature observations of Mars. In particular, thermal inertia from Viking, Mars Global Surveyor (MGS), and Mars Odyssey data has been derived and mapped with increasing spatial resolution, in each case providing an improved understanding of the surface layer. In addition, local-scale observations from the Mars Exploration Rovers (MERs) have provided in situ thermal inertia ground truth of characteristic soils and rocks. Overall, the surface of Mars is dominated by soils to a depth of a few centimeters or more.