Thermal Conductivity Studies of Sedimentary Materials from Central Australia and the Implications for Mars

Introduction: In the search for life on Mars, investigating fluvial deposits will be a high priority for future landers. Although there is abundant evidence that fluvial processes worked with great intensity in the past (e.g., outflow channels, valley networks, and modified impact craters), aeolian processes dominate under the current environmental conditions. In fact there is evidence that extensive aeolian deposits may have filled in valley networks [1] and even shallow depressions where water may have ponded [2]. Thus, quite often there may be a disparity between the geology identified by orbital data and the geology accessible to a lander. Determining where fluvial deposits occur on the surface is important for addressing NASA's goal to "follow the water." In order to do that, however, existing remote sensing data must be evaluated and a set of diagnostic criteria for recognizing fluvial deposits must be established. To that end, we are conducting a first order analysis of the thermal characteristics of fluvial and aeolian materials collected from central Australia. Thermal Inertia: One of the most fundamental characteristics needed to describe a sedimentary deposit is grain size. Indirectly, thermal infrared data from Viking IRTM, MGS TES, and Odyssey THEMIS can provide an estimate of the grain size of martian surface materials by measuring surface temperature variations [3,4]. Thermal inertia is a measure of how rapidly the surface responds to changes in thermal energy. It is controlled primarily by the thermal conductivity of the surface material, which is itself a function of bulk density, grain size, and grain size distribution. To date there has only been one comprehensive study of the thermal conductivity of particulate materials under martian atmospheric conditions where the importance of these various characteristics were explored [5]. While this study provided many important insights on how the physical characteristics of a particulate material influences the thermal conductivity, most of the measurements were performed on glass beads. Natural materials, however, are much more complicated. For example, angularity can affect the bulk density of a material. Water can also carry dissolved salts and suspended clay that can provide bonds between the sediment grains once deposited and desiccated, thus increasing the effective particle size. To explore the thermal behavior of natural sedimentary materials, we