Thermal Inertia and Conductivity Measurements of Mars Analog Samples

Thermal inertia (I) is the intrinsic property of a material that describes how efficiently that material can store, conduct, and re-radiate heat. It
is given by: = sqrt() (1) where k is the bulk thermal conductivity (W/mK), ρ is the bulk density (g/cm3), and c is the specific heat (J/K); I has units of J/m2Ks1/2. At Mars atmospheric pressures (1-10 mbar), thermal inertia is dominated by the effects of thermal conductivity, which in turn is determined by the physical characteristics of near subsurface (upper few cm) geologic materials [1,2]. Examples of such physical properties include grain size (for unconsolidated sediment), degree of induration or cementation, vesicularity, porosity, or degree of fracturing. Many laboratory studies have related the physical properties of geologic particulates to their thermal properties [3-8]. However, methods have been inconsistent between laboratories and only a few studies have measured thermal properties in Mars-relevant pressures [e.g. 4]. Presley and Christensen conducted a number of studies [5-8] using a line-heat source apparatus in a Mars-like atmosphere and determined a quantitative relationship between unimodal and bimodal grain size samples and thermal properties. However, no thermal measurements at Mars pressures exist for solid samples, and quantitative relationships between thermal conductivity and rock porosity, mechanical strength [9], and density have not been determined for Mars conditions. This work aims to close the gaps in our understanding of thermal properties as they relate to physical characteristics of rocks and sediment on both Earth and Mars, while quantifying relationships between thermal properties on Earth and in Mars conditions for easier comparison of analog samples in the future.

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