Thermal Conductivity Measurements of Natural Eolian and Fluvial

Introduction: The particle size of surficial materials may provide important clues about the history of erosion, transport, and depositional processes that have acted to form the deposit. Particle size may also provide a valuable clue about the genesis of those deposits. On Mars, most of the surface is covered with at least a thin coating of various particulate materials that tend to obscure direct evidence of bedrock [e.g., 1-3]. Thus, one of the primary goals of Martian studies and exploration [e.g., 4-5] has been to understand the nature of the Martian surface materials and to decipher their relationships with bedrock geology. Global maps that present estimations of the thermal inertia of Martian surface materials have been created with surface temperature data gathered Variations in thermal inertia primarily are due to variations in the thermal conductivity [8] under Martian atmospheric conditions. Laboratory measurements have shown that for Martian atmospheric pressures the thermal conductivity of particulate materials has a strong dependence on the particle size [9-11]. In particular, the log of thermal conductivity exhibits a linear relationship to the log of the particle size at any given atmospheric pressure, at least up to 100 torr [12]. A combination of these concepts should allow a reasonable estimate of an effective particle size of the Martian surficial deposits. The most comprehensive study of the effects of particle size on thermal conductivity under Martian atmospheric conditions [12], however, used very narrow particle size ranges and spherical glass beads in order to establish an empirical relationship. Can this empirical relationship be applied to real surficial deposits, with non-spherical particle shapes and that consist of well-to poorly-sorted mixtures of particle sizes? Samples: Eight samples were collected from various eolian and fluvial environments in the Simpson Desert, Australia [13]. At each site, a Model 3440 portable surface moisture density gauge manufactured by Troxler Electronic Laboratories was used to measure the bulk density of the sample in situ, before collection, so that the bulk density could