Stratigraphy of Promethei Lingula, south polar layered deposits, Mars, in radar and imaging data sets

Abstract

The south polar layered deposits (SPLD) of Mars have been studied through imagery for decades. Now, two subsurface sounding radar instruments have collected data: the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on Mars Express and the Shallow Radar (SHARAD) instrument on Mars Reconnaissance Orbiter are observing the SPLD at multiple frequencies (1.8–5 and 20 MHz, respectively). Both instruments detect subsurface reflections in the Promethei Lingula region of the SPLD. MARSIS detects up to three reflections within Promethei Lingula, in addition to detecting the basal contact between the SPLD and the underlying plains. SHARAD detects 10s of reflections without penetrating to the base of the SPLD. MARSIS reflections likely correlate to the boundaries of packets of reflections in the SHARAD data; whatever change in composition of the SPLD that causes the SHARAD reflections to occur in packets may also be the source of the MARSIS reflections. In several locations, SHARAD reflections can be compared directly with images of layers; an individual reflection corresponds to 3–7 layers in images at resolutions of 6 m/pixel. Reflection surfaces are calculated using the radar observations and extrapolated to the SPLD margins where they are compared to the stratigraphy observed in images. We find that the MARSIS reflections, and thus the packet structure within the SHARAD observations, are likely related to distinctive groups of layers rather than individual layers. The radar data sets allow us to confirm several predictions concerning the interior of the SPLD from stratigraphic studies of images, including that most of the layers extend throughout the region and that they decrease in elevation toward the margin of the SPLD.