Radar properties of the Dorsa Argentea Formation, Mars determined from SHARAD and MARSIS data

The Dorsa Argentea Formation (DAF) is an extensive Hesperian-aged deposit surrounding the south polar layered deposits on Mars. Several formation hypotheses have been put forward to explain the DAF emplacement, including volcanic activity, debris flows, aeolian deposition, and glacial activity. Recently, the ancient ice sheet formation hypothesis has been favored, with many landforms in the DAF interpreted to form from removal of ice or in the presence of ice-rich materials. If the DAF does represent the remnants of an ancient ice sheet, then it may preserve an ancient record of climate on Mars. Here we use the SHARAD and MARSIS datasets to investigate the extent and radar properties of the DAF, including loss tangent. The frequencies of these two sounding datasets are complementary and enable an analysis of the DAF basal reflector and shallower near-surface reflectors. SHARAD data processed using an incoherent summing technique that increases the signal-to-noise ratio were analyzed for subsurface reflectors that overlap the DAF. Approximately 40 SHARAD tracks with reflectors were identified. These reflectors are very shallow and may represent a mantling-type deposit on the surface of the DAF. Over 250 MARSIS subsurface reflectors coincide with the mapped extent of the DAF. The composition of the materials between the surface and subsurface reflectors was determined by calculating loss tangent, which can be used to distinguish between geologic materials such as water ice, dry sediment, and basalt. The power of the surface and subsurface reflectors, as well as the change in the power with depth, were used to calculate loss tangent. Loss tangent values determined with MARSIS span a large range, with values consistent with water ice to basalt. However, the loss tangent values corresponding to dry sediment and basalt have higher confidence values than any of the water ice values. Based on the calculations performed thus far, the DAF are more consistent with dry sediment and basalt. These higher loss tangent values occur in some of the thickest regions of the DAF. The average thickness of the DAF is on the order of 0.5 km, depending on the exact composition of the deposit. These results suggest that the DAF has less ice present than previously hypothesized.