Specific Heat Capacity Measurements of Selected Meteorites for Planetary Surface Temperature Modeling

Specific heat capacity Cp(T) is an intrinsic regolith property controlling planetary surface temperatures along with the albedo, density, and thermal conductivity. Cp(T) depends on material composition and temperature. Generally, modelers assume a fixed specific heat capacity value, or a standard temperature dependence derived from lunar basalts, mainly because of limited composition-specific data at low temperatures relevant to planetary surfaces. In addition, Cp(T) only appears to vary by a small factor across various materials, in contrast with the bulk regolith thermal conductivity, which ranges over ~3-4 orders of magnitude as a function of the regolith physical state (grain size, cementation, sintering etc.). For these reasons, the impact of the basaltic assumption on modeled surface temperature is often considered unimportant although this assumption is not particularly well constrained. In this paper, we present specific heat capacity measurements and parameterizations from ~ 90 to ~ 290 K of 28 meteorites including those possibly originating from Mars, and Vesta, and covering a wide range of planetary surface compositions. Planetary surface temperatures calculated using composition-specific Cp(T) are within ± 2 K of model runs assuming a basaltic composition. This ± 2 K range approaches or exceeds typical instrumental noise or other sources of modeling uncertainties. These results suggest that a basaltic assumption for Cp(T) is generally adequate for the thermal characterization of a wide range of planetary surfaces, but possibly inadequate when looking at leveraging subtle trends to constrain subsurface layering, roughness, or seasonal/diurnal volatile transfer.