Linking Thermal Properties of Terrestrial Sedimentary Environments to Mars

Despite nearly complete coverage of the Martian surface with thermal infrared datasets, uncertainty remains over a wide range of observed thermal trends. Combinations of grain sizes, packing geometry, cementation, volatile abundances, subsurface heterogeneity, and sub-pixel horizontal mixing lead to multiple scenarios that would produce a given thermal response at the surface. Sedimentary environments on Earth provide a useful natural laboratory for studying how the interplay of these traits control diurnal temperature curves and identifying the depositional contexts those traits appear in, which can be difficult to model or simulate indoors. However, thermophysical studies at Mars-analog sites are challenged by distinct controls present on Earth, such as soil moisture and atmospheric density. In this work, as part of a broader thermophysical analog study, we developed a model for determining thermal properties of in-place sediments on Earth from thermal imagery that considers those additional controls. The model uses Monte Carlo simulations to fit calibrated surface temperatures and identify the most probable dry thermal conductivity as well as any potential subsurface layering. The program iterates through a one-dimensional surface energy balance on the upper boundary of a soil column and calculates subsurface heat transfer with temperature-dependent parameters. The greatest sources of uncertainty stem from the complexity of how thermal conductivity scales with water abundance and from surface-atmosphere heat exchange, or sensible heat. Using data from a 72-hr campaign at a basaltic eolian site in the San Francisco Volcanic Field, we tested multiple models for how dry soil components and water contribute to thermal conductivity and multiple approaches to estimating sensible heat from field measurements. Field measurements include: upwelling and downwelling radiation, air temperature, relative humidity, wind speed, and soil moisture, all collected from a ground station, as well as UAV-derived surface geometries. By mitigating Earth-specific uncertainty and isolating the controls that are most relevant to Martian sediments, we can then validate those controls with in situ thermophysical probe measurements and ultimately improve interpretations of thermal data for the Martian surface.