The history of ground ice at Jezero Crater Mars and other past, present, and future landing sites

Shallow subsurface water ice on Mars is currently stable poleward of about 45° latitude and unstable in the equatorial regions. Past climate cycles driven by orbital oscillations are expected to result in significant changes to this distribution of ground ice over geologic history. In the present study we model the 2.5-Myr history of ground ice at 11 past, present, and planned future landing sites, employing new views of the martian climate and new ground truth observations. We specifically evaluate the potential for detecting ground ice at current and future GPR-equipped-rover landing sites at Jezero Crater, Utopia Planitia, and Oxia Planum. We find that, while ground ice is stable at the past Phoenix and Viking Lander 2 sites, it is presently unstable at all others. However, ground ice would have been stable at all the landing sites for extended periods of 10's of kyrs when the obliquity exceeded about 29°–33°. The most recent such episode would have occurred about 500 kyrs ago. On thousand-year time scales water-vapor diffusion through porous soil and ice condensation are rapid enough to keep pace with these climate changes, such that the presence of ground ice can be equated with its stability. Prior to 5 Myr ago the obliquity is predicted to have experienced a secular shift to a higher average of ~36°. During this time extensive subsurface ice deposits may have formed that may persist unstably today as a relict of this past condition.