How do large-scale impacts modulate the depth of groundwater on Mars through time?

Liquid water has shaped the surface of Mars throughout most of the planetary history. Geomorphological analysis, spectroscopic investigations to generate mineralogical surface maps, and rover measurements show evidence for outflow channels, valley networks, deltas (e.g., Fasset & Head, 2007; De Toffoli et al., 2021), sedimentary deposits (e.g., McLennan et al., 2019), hydrated minerals (e.g., Ehlmann & Edwards, 2014), cementation (e.g., McLennan et al., 2005) and mineral veins containing, e.g., manganese oxides that require water (e.g., Lanza et al., 2016). Such features, amongst many others, suggest that liquid water was present at the surface and in the subsurface of Mars throughout the Noachian and in transient episodes during the Hesperian and Amazonian (e.g., Carr & Head, 2010; Grotzinger & Milliken, 2012), which has important implications for the habitability of the planet.

Today, liquid water is generally thermodynamically no longer stable at the surface due to the low surface temperature and pressure conditions. However, liquid groundwater may still exist in the martian subsurface (Clifford et al., 2010; Stamenkovic et al., 2019). Due to limited crustal recycling on Mars, a significant amount of water may still exist today underground as ice, as liquid water, or mineral-bound in the crust. Evidence for such a global groundwater system on early Mars has been reported by Salese et al. (2019).

In this study, we perform global-scale geodynamic thermal evolution models of the interior of Mars (Plesa et al., 2018) and track the spatial variations in temperature during the thermal evolution, by solving numerically the conservation equations of mass, linear momentum, and thermal energy. Our models use an interior structure compatible with seismic data recorded by InSight (Stähler et al., 2021; Knapmeyer-Endrun et al., 2021; Wieczorek et al., 2022), a pressure- and temperature-dependent viscosity following an Arrhenius law (Hirth & Kohlstedt, 2003), and consider the effects of core cooling and radioactive decay as appropriate for thermal evolution modeling. Our models include a spatially variable crustal thickness that is modified with time by large-scale impacts, leading to crustal thinning at the impact location. The impact-induced thermal anomaly is considered in our models by using scaling laws from Melosh (1989), that relate the temperature increase at the impact location to parameters such as projectile size, velocity, and density, as well as target density.

Coupling the geodynamic evolution with large-scale impacts leads to an increase of subsurface temperature due to impact induced heating and, at the same time, a faster cooling due to a thinner crust, whose insulating effect is strongly reduced. The competition between the heating and cooling of the subsurface due to impacts will naturally affect the evolution of the subsurface temperature on Mars. Since the depth groundwater critically depends on the thermal state of the subsurface, with our models, we will test how large-scale impacts modulate the evolution of groundwater in the martian subsurface.

Future work will couple the geodynamic evolution with impact models (Manske et al., 2025) and incorporate water-rock reactions (Huber et al., 2024; Grund et al., 2025) to evaluate the overall subsurface water budget of Mars. This multidisciplinary approach will provide new insights into the formation and evolution of groundwater on Mars and its potential for supporting habitable niches in the Martian subsurface.

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