Magmatic pathways for subsurface habitability on Mars

Terrestrial microbial life is documented in micrometer-scale rock pores in boreholes and mines as deep as 5 km.  If life ever emerged in Mars, it may still survive actively at similar depths in the Martian crust, where temperatures are above zero Celsius. Since such Martian depths are out of reach for present technology, we set off to conceive Martian settings where putative life could be active closer to the surface.One possible way for microbial life to approach the Martian surface is by using the warmth of eruptions to migrate parallel to magma vents, at distances where temperature is above 0 C. Magmatic activity creates dikes and surface lava flows with basalt at about 1250 C, transitorily increasing the temperature of the surrounding crust. We hypothesize that the cooling rates may be slow enough for Earth-like microbial-life to migrate through these warm corridors and approach the surface.Bacteria and Archea swim at velocities faster than 250 m/yr and migrate through rock pores with highly variable motilities of 28 m/yr and higher (Horvath et al., 2021; Jin and Sengupta, 2024; Nishiyama and Kojima, 2012), depending on porosity types and fracturing. InSight data suggests a weakened Martian crust compatible with intense fracturing and high porosity infilled with water (Li et al., 2023), probably caused by the multi-billion-year long exposure to meteoritic impacts. Open fractures are hypothesized to be particularly prominent around and above magmatic dikes in Martian conditions due to stresses related to magma injection and later cooling (Rivas-Dorado et al., 2023). The lower Martian gravity should minimize mechanical and chemical pore compaction, contributing to make the Martian underground more passable than in Earth’s. We therefore test whether bacterial-like migration velocities can defeat post-magmatic underground cooling in Mars following a magmatic event and actively approach the surface. To this purpose, we perform diffusive thermal relaxation modeling of the subsurface inspired by the Elysium and Cerberus Fossae region, where 53,000 to 210,000 years old eruptions have been identified (Horvath et al., 2021). We constrain the magmatic intrusion’s geometry based on dike modeling (Rivas-Dorado et al., 2022) and on observed lava flows (Cataldo et al., 2015), supported by published interpretations of InSight seismic data. The results suggest that dike sizes are consistent with a passable pathway above freezing temperature propagating slower than Earth-like microbial motility. We constrain minimum depths reachable by hypothetical bacterial-like underground organisms as a function of realistic Martian magmatic intrusion parameters.