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The long-term geological evolution of a planet is dependent on the bulk concentration of the long-lived heat-producing element (HPE; 238 U, 235 U, 232 Th, and 40 K) and their distribution between the crust and the mantle. High enrichment of HPE in the crust depletes the mantle of heat production and lowers the mantle potential temperature. In contrast, crust with lower enrichment of HPE thermally insulates the mantle increasing the mantle potential temperature (e.g., O'Neill et al., 2005). The thermal state of a planet's mantle modulates its convection, which influences volcanism, crustal tectonics, and geomagnetism (e.g., Stevenson, 2007). These geological processes directly impact hydrospheric and atmospheric processes (e.g.,

Heat is primarily generated in planetary interiors by the decay of long‐lived heat producing elements (HPE). Planetary heat flow estimates can thus provide critical insights into the thermal state of a planet and the bulk distribution of the HPE. The lack of appreciable lithospheric deflection in the north polar region of Mars by the weight of the polar ice cap is suggestive of low heat flow. Here we model the deflection of the Martian lithosphere and show that the present‐day mantle heat flow cannot exceed 7 mW m−2 in the north polar region of Mars. Our mantle heat flow estimate is notably lower than the heat flow expected from a chondritic mantle suggesting the Martian mantle to be depleted in HPE. If our result is globally representative, lower levels of heat generation in the planet's mantle may have inhibited widespread late‐stage volcanism on Mars.

Long-lived hydrothermal systems are prime targets for astrobiological exploration on Mars. Unlike magmatic or impact settings, radiogenic hydrothermal systems can survive for >100 million years because of the Ga half-lives of key radioactive elements (e.g., U, Th, and K), but remain unknown on Mars. Here, we use geochemistry, gravity, topography data, and numerical models to find potential radiogenic hydrothermal systems on Mars. We show that the Eridania region, which once contained a vast inland sea, possibly exceeding the combined volume of all other Martian surface water, could have readily hosted a radiogenic hydrothermal system. Thus, radiogenic hydrothermalism in Eridania could have sustained clement conditions for life far longer than most other habitable sites on Mars. Water radiolysis by radiogenic heat could have produced H2, a key electron donor for microbial life. Furthermore, hydrothermal circulation may help explain the region’s high crustal magnetic field and gravity anomaly.

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