Paul Morgan

Diurnal and seasonal variations in soil and surface temperature measured with the thermal probe and radiometer of NASA's InSight Mars mission are reported. At a representative depth of 10–20 cm, an average temperature of 217.5 K was found, varying by 5.3–6.7 K during a sol and by 13.3 K during the seasons. From the damping of the temperature variation with depth and the phase shift, a thermal diffusivity of (3.93 0.39) × /s was derived for the upper 10 cm from the diurnal temperature variation and of (3.63 0.53) × /s for the 40 cm depth range of the mole from the annual temperature variation. Using published thermal conductivity and inertia values together with the diffusivities, soil densities of 1,470 and 1,730 kg/ were derived for these depths. The temperatures allow the deliquescence of thin films of brine, the efflorescence of which may explain the cemented duricrust observed.

Temperature is of primary importance for many physical properties in the Martian soil. We measured diurnal and annual soil (and surface) temperature variations using the NASA InSight Mars mission’s HP3 radiometer and thermal probe. At the depth of the probe of 0.5 - 36 cm, an average temperature of 217.5K was found varying by 5.3 - 6.7 K during a sol and by 13.2K during the seasons. The damping of the surface temperature variations in the soil were used to derive a thermal diffusivity of 2.30±0.03×10−8 m2/s for the depth range of the diurnal wave - thermal skin depth 2.5±0.04 cm - and 3.74±0.61×10−8 m2/s for that of the annual wave, with a thermal skin depth of 84±10 cm. The temperatures measured are conducive to the deliquesence of thin films of brines in the soil. These are of astrobiological interest and may explain the formation of the observed cemented duricrust.

In this study, the Energy and Carbon Management Commission (ECMC), Colorado Geological Survey (CGS), and Teverra collaboratively completed a comprehensive review of Colorado’s geologic and geothermal history, a data review and resource assessment, a utilization and market analysis, and a corresponding environmental and regulatory evaluation of the geothermal opportunities in Colorado. Presented in this report are the results, conclusions, and recommendations of this work. Past geothermal studies (Appendix A) in Colorado highlighted that the state's geologic profile supports varied geothermal resources and displays high potential for development. Colorado is executing an inclusive strategy to take advantage of federal incentives and initiatives. Colorado has leveraged tens of millions of dollars in support of the emerging geothermal energy market through state incentives to further complement the growing momentum in the sector. Encouraged by outreach and engagement efforts of the Colorado Energy Office and other agencies, communities and utilities are joining the conversation about how geothermal energy can be a part of the clean energy transition.

In this study, the Energy and Carbon Management Commission (ECMC), Colorado Geological Survey (CGS), and Teverra collaboratively completed a comprehensive review of Colorado’s geologic and geothermal history, a data review and resource assessment, a utilization and market analysis, and a corresponding environmental and regulatory evaluation of the geothermal opportunities in Colorado. Presented in this report are the results, conclusions, and recommendations of this work. Past geothermal studies (Appendix A) in Colorado highlighted that the state’s geologic profile supports varied geothermal resources and displays high potential for development. Colorado is executing an inclusive strategy to take advantage of federal incentives and initiatives. Colorado has leveraged tens of millions of dollars in support of the emerging geothermal energy market through state incentives to further complement the growing momentum in the sector. Encouraged by outreach and engagement efforts of the Colorado Energy Office and other agencies, communities and utilities are joining the conversation about how geothermal energy can be a part of the clean energy transition.

The heat flow and physical properties package measured soil thermal conductivity at the landing site in the 0.03–0.37 m depth range. Six measurements spanning solar longitudes from 8.0° to 210.0° were made and atmospheric pressure at the site was simultaneously measured using InSight's Pressure Sensor. We find that soil thermal conductivity strongly correlates with atmospheric pressure. This trend is compatible with predictions of the pressure dependence of thermal conductivity for unconsolidated soils under martian atmospheric conditions, indicating that heat transport through the pore filling gas is a major contributor to the total heat transport. Therefore, any cementation or induration of the soil sampled by the experiments must be minimal and soil surrounding the mole at depths below the duricrust is likely unconsolidated. Thermal conductivity data presented here are the first direct evidence that the atmosphere interacts with the top most meter of material on Mars.

The heat flow and physical properties package measured soil thermal conductivity at the landing site in the 0.03 to 0.37 m depth range. Six measurements spanning solar longitudes from 8.0$^\circ$ to 210.0$^\circ$ were made and atmospheric pressure at the site was simultaneously measured using InSight’s Pressure Sensor. We find that soil thermal conductivity strongly correlates with atmospheric pressure. This trend is compatible with predictions of the pressure dependence of thermal conductivity for unconsolidated soils under martian atmospheric conditions, indicating that heat transport through the pore filling gas is a major contributor to the total heat transport. This implies that any cementation or induration of the soil sampled by the experiments must be minimal and that the soil surrounding the mole at depths below the duricrust is unconsolidated. Thermal conductivity data presented here are the first direct evidence that the atmosphere interacts with the top most meter of material on Mars.

The heat flow and physical properties package (HP³) of the InSight Mars mission is an instrument package designed to determine the martian planetary heat flow. To this end, the package was designed to emplace sensors into the martian subsurface and measure the thermal conductivity as well as the geothermal gradient in the 0–5 m depth range. After emplacing the probe to a tip depth of 0.37 m, a first reliable measurement of the average soil thermal conductivity in the 0.03–0.37 m depth range was performed. Using the HP³ mole as a modified line heat source, we determined a soil thermal conductivity of 0.039 ± 0.002 W m⁻¹ K⁻¹, consistent with the results of orbital and in‐situ thermal inertia estimates. This low thermal conductivity implies that 85%–95% of all particles are smaller than 104–173 μm and suggests that soil cementation is minimal, contrary to the considerable degree of cementation suggested by image data. Rather, cementing agents like salts could be distributed in the form of grain coatings instead. Soil densities compatible with the measurements are kg m⁻³, indicating soil porosities of %.