We surveyed the subsurface structure of Chryse and Acidalia Planitiae using data from the Mars SHAllow RADar sounder (SHARAD) onboard the Mars Reconnaissance Orbiter (MRO). Several subsurface reflectors were identified in these regions, but these reflectors do not constitute apparent subsurface structures larger than 30 km. The bulk dielectric constants of the uppermost layers at two locations were estimated as 5.3 and 5.9 from the combination of high-resolution images and topographic data. These values were used to constrain the possible bulk porosity (approximately 28 % and 25 %) and the upper limit for the volume fraction of water ice (~43 % and ~50 %). The estimated porosities of the shallow subsurface layers in these locations can be explained by the emplacement of basaltic rock or till that may contain some ice-cemented regolith.

We surveyed the subsurface structure in eastern Coprates and Capri Chasmata in the equatorial region using high-resolution visible images, digital terrain models, and radar sounding data. We identified subsurface reflectors in four areas of the chasmata. At the stratigraphic exposure on the chasmata walls, the corresponding depth of the reflector is ~60 m. The bulk dielectric constants of the layers above the reflectors are calculated as 3.4-4.0, suggesting a rock-air mixture with ~46.1% porosity, or a rock-air-ice mixture with ~21.2% water-ice fraction. Recent climate models suggest that water-ice is unstable on the surface around the equatorial regions. However, considering the recent high obliquity that occurred ~0.4 Ma and a slow diffusivity of water-ice, the existence of subsurface water-ice deeper than a few meters cannot be ruled out. If water-ice is actually contained in the layer, our results show the maximum volume of putative water-ice in the chasmata is 16.6 km.