The Impact of Astronomically Induced Insolation Variations on the Extent of the Martian Cryosphere

Introduction: Estimates of the global inventory of water on Mars based on a determination of the amount of water required to erode the outflow channels suggest that a quantity equivalent to a global ocean 0.5 to 1 km deep may be stored in the planet’s subsurface [1, 2]. As this inventory post dates the timing of the most efficient processes that may have lead to its removal, the majority of this water is expected to survive to the present day as subsurface ice and groundwater (e.g. [3, 4]). In this work, we examine the impact of climatic insolation variations on the extent of the Martian cryosphere – with particular regard to the occurrence of thawing in both the deepand near-subsurface that could promote hydrous alteration. Recent calculations show that the globally averaged depth of the cryosphere of Mars may be twice as deep as previously estimated [5], although spatial heterogeneities in crustal heat flow, thermal conductivity, and freezing point depression may result in substantial local variations in cryosphere thickness about this mean. Here we demonstrate that climatic variations in insolation may result in km-scale variations in cryosphere thickness at high latitudes over the past 20 million years. We also demonstrate that extensive thawing of the near-subsurface may occur at midto high-latitudes at time of high obliquity. Implications on the aqueous processes of the subsurface of Mars and on the presence of subpermafrost groundwater are examined.