Recent Widespread Deposition in the Martian North and South Polar Layered Deposits As Revealed by Multiband SHARAD Surface Reflectivity

The north and south polar layered deposits (PLD) on Mars are composed of stacks of layered ice and dust, but the SPLD is approximately twice as bright as the NPLD in 20-MHz radar echoes. We use Shallow Radar (SHARAD) data in similar to 4-MHz bands centered on 17.5 MHz ("L") and 22.5 MHz ("H") to determine whether radar reflectivity variations are due to scattering effects related to closely spaced, near-surface dielectric layering. We mapped the ratio of the surface echo power at the two frequencies (H/L) for both PLDs. The NPLD has large areas where H and L echo power differ, consistent with destructive interference in the H band within the uppermost similar to 20 m. The SPLD is dominated by H similar to L (unity), except for isolated regions in and near the residual CO2 cap and Australe Lingula. The H/L variations can be partly explained by near-surface structure, where large variations in H/L match locations with numerous near-surface reflecting interfaces, and locations where H similar to L may contain few such reflectors. There is no obvious connection between H/L and surface morphology, but the distribution of non-unity H/L resembles the extent of a widespread, recent accumulated package (WRAP) at both poles. The spatial association between H/L and WRAP and interference indicated by H/L suggests that large regions in the NPLD-and isolated areas in the SPLD-are characterized by shallow layer(s) of consistent thickness/separation potentially deposited within the past few tens of kyr as Mars emerged from the last obliquity-driven ice age. The north and south poles of Mars reflect radar energy differently, where the south polar region is more reflective than the north. We used radar data from the Shallow Radar instrument to investigate how the near-surface ice and dust layering could affect reflectivity. We found that the north polar region is more densely layered near the surface, leading to radar signal interference that changes the reflectivity. The south polar region, in contrast, has fewer near-surface reflectors in many locations. Both poles show evidence of interference in similar locations as a widespread young deposit of ice and dust layers that formed in the past similar to 300,000 years. Since our data (which describe to the top several meters of the surface) suggest interference occurs in regions similar to this young deposit, one explanation is that these regions of strong radar interference accumulated over the past similar to 20,000 years. North and south polar layered deposits have different radar surface reflectivities due in part to layering in the uppermost similar to 20 m Interference effects in radar scattering occur more often in the densely layered north polar deposits Differences in reflectivity and near-surface structure could indicate the extent of recent ice/dust accumulation in the past similar to 20 kyr