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.

Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, contains a carbonate-bearing rock unit termed the margin fractured unit. Some of the carbonates in these rocks may have formed in a fluviolacustrine environment and therefore could preserve biosignatures of paleolake-inhabiting lifeforms. Here we evaluate whether these margin fractured unit carbonates formed as authigenic precipitates in a fluviolacustrine environment or via alteration of primary minerals by groundwater. We integrate thermal inertia measurements from the Thermal Emission Imaging System (THEMIS), spectral analyses from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), examination of stratigraphic relationships in Jezero crater using High Resolution Science Experiment (HiRISE) and Context Camera (CTX) images and digital elevation models. We also compare the Jezero crater results to observations from the Curiosity rover in Gale crater. We find that margin fractured bedrock with the deepest visible-to-near-infrared carbonate absorptions also has exceptionally high thermal inertia and thickness relative to other carbonate-bearing units in Jezero crater, consistent with enhanced cementation and crystallization by groundwater. Our results indicate that it is equally likely that carbonates in Jezero crater formed via alteration of primary minerals by alkaline groundwater rather than as authigenic precipitates in a fluviolacustrine environment. Jezero crater may have hosted ancient subsurface habitable environments related to these groundwaters, where life-sustaining redox energy was generated by water-rock interactions. The Mars 2020 Perseverance rover could encounter biosignatures preserved from this carbonate-forming environment, whether it was fluviolacustrine or in the subsurface.