The Composition of the South Polar Cap of Mars Derived From Orbital Data

Abstract

The flexure of the lithosphere under stresses imposed by the geologically young south polar cap is one of the few clues we have regarding the south polar cap composition and the present-day thermal state of Mars. Here, we combine radar, gravity, and topography data with a flexural loading model to estimate the bulk density ((Formula presented.)) and average real dielectric constant ((Formula presented.)) of the south polar cap, and the elastic thickness of the lithosphere ((Formula presented.)). Given the uncertainties of the data, our results constrain (Formula presented.) to be 1,100–1,300 kg (Formula presented.) (best fit of 1,220 kg (Formula presented.)), (Formula presented.) to be 2.5–3.4 (best fit of 3.3), and (Formula presented.) to be greater than 150 km (best fit of 360 km). Based on these results, the maximum lithospheric flexure is 770 m, and the polar cap volume could be up to 26% larger than previous estimates that did not account for lithospheric flexure. Our inferred compositions imply that the dust concentration would be at least 9 vol% if the (Formula presented.) ice content were negligible, and that the (Formula presented.) ice concentration would be more than the known 1 vol% (Formula presented.) if the dust concentration were less than 9 vol%. The 1- (Formula presented.) lower limit on (Formula presented.) implies a surface heat flow that is less than 23.5 mW (Formula presented.). This lower limit is significantly less than the range of acceptable values at the north pole (330–450 km, heat flow of 11–16 mW (Formula presented.)), and helps satisfy global thermal evolution simulations that predict hemispheric differences in surface heat flow. © 2021. American Geophysical Union. All Rights Reserved.