The Beginning of Mars Subsurface Hydrology in 4D

The Martian subsurface has had and still has the potential to enable environments with stable groundwater. The possibility of such underground waters has gained more interest since the announcement of a possible subsurface lake beneath the South Polar Layered Deposits on Mars with MARSIS [1]. The temperature at the base of these polar deposits at 1.5 km has been estimated to be 205 K, which would require large amounts of dissolved salts (likely Ca- or Mg-perchlorates) to sufficiently reduce the freezing point of water. Due to attenuation, MARSIS and SHARAD have generally great difficulties to detect groundwater beneath a depth of a few hundred meters, particularly at an aquifer horizontal scale of less than a few tens of km and away from the polar caps. Since initial estimates of the groundwater table are generally far beyond a depth of 1 km, Martian groundwater might be much more widespread but has so far not just remained undetected but was rather undetectable.

We show results of 4D (three in space and one in time) interior models of Mars that self-consistently compute the subsurface thermal profile, groundwater stability depth, porosity, and permeability as a function of location and planet age across the last 4.5 billion years. The two models used are (A) a 3D spherical full mantle convection [3] and (B) a parameterized thermal evolution model both coupled to a 3D crustal model that is compatible with today's gravity and topography data. The spherical full mantle convection model explicitly considers both lateral variations of the crustal and mantle heat flow contributions, which can lead to regional perturbations that can shift the groundwater table closer to the surface. The advantage of the parameterized evolution model on the other hand is the inclusion of various uncertainties in planet & model conditions and brine properties.

We show how groundwater levels vary as a function of location on Mars today and across time, and discuss implications for potential aquifers beneath the polar ice caps and for current and future landed Mars assets.

References: [1] Orosei et al., Science 2018; [2] Clifford et al., JGR, 2010; [3] Plesa et al., JGR, 2016

This work was performed in part at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. © 2018, California Institute of Technology.