Constraining the CO2 Thickness and the Dust Content of Layers within the South Polar Layered Deposits of Mars from Radar Forward Modeling

CO2 gas composes ~95% of the Martian atmosphere and approximately 2530% of the atmosphere is exchanged with the polar caps annually. The exact mass distribution between the CO2 gas and ice phases varies seasonally and spatially over the pole. Changes in obliquity, season of perihelion, and other orbital parameters affect the CO2 cycle, including the amount and extension of the seasonal dry-ice. Condensation and sublimation of CO2 at high latitudes controls atmospheric circulation on a global scale and is thus a crucial aspect for understanding the Martian climate. Orbital penetrating radar has been used for climate studies to probe the interior of the PLD to variable depths. Shallow Radar (SHARAD) in particular has been used to understand the radar behaviors of the SPLD/NPLD. Echoes from the SHARAD instrument onboard the Mars Reconnaissance Orbiter have showed multilayered internal structure with dozens of internal reflections running parallel or sub parallel to the surface, some of them quickly attenuate across most of the SPLD, but many of them traceable over distances up to 100km. We will present an analysis at the south pole of Mars, the thicker poleward portions of the SPLD. Analysis of radar two-way delay between the surface reflections and reference subsurface reflectors will be conducted over multiple orbital tracks acquired at different seasons and over the same regions, in order to estimate the change in the seasonal CO2 frost thickness and quantify the spatial variation as a function of time and latitude. Finally, we will show that the estimates obtained from the direct measurements described above can be used along with other a priori information for constraint the dielectric properties of the entire column using a multilayer simulator. Despite differing methodology with previous works, our minimum layer permittivity results agree well with the past results obtained by past studies, suggesting that SPLD consists of superposed thin layers of water ice contaminated by a variable amount of mineral dust (015%). The work presented here has been developed within the framework of a two years project funded by the NASA Postdoctoral Program, Universities Space Research Association. 2021 All rights reserved. California Institute of Technology. Government sponsorship acknowledged.