Radar Constraints On The Thickness Of Subsurface Ice Near Hellas Planitia, Mars

Abstract

Geomorphological features potentially related to subsurface ice, such as scalloped depressions, expanded craters, pedestal craters, lobate debris aprons, and banded terrain, are present in Hellas Planitia, Mars. We surveyed the region using the Shallow Radar instrument on the Mars Reconnaissance Orbiter to identify candidate subsurface reflectors that may be due to the presence of ice-rich layers. We found that the majority of possible subsurface returns are likely caused by reflections from off-nadir surface topography. However, there are some candidate reflectors in which we have higher confidence, including several adjacent reflectors likely associated with an ice-rich unit mantling a plateau. We also identified basal reflectors of a lobate debris apron consistent with a dielectric constant of relatively pure ice. Additionally, we characterized the candidate reflectors near scalloped depressions, expanded craters, and pedestal craters, and calculated the depths of the reflectors assuming endmembers of pure ice and basalt in order to constrain the possible range of thicknesses for an ice-rich layer. The ice could be thicker than 100 m if the reflectors originate from the base of a pure ice layer. A mixed ice and rock layer would be thinner. We do not find evidence of reflectors associated with banded terrain.