Characterizing Seasonal and Residual Ices at the South Pole of Mars Using a Universal Set of CRISM Spectral Endmembers

Current maps of compositional variation across south polar ice exposures on Mars do not resolve the meter-scales at which erosional processes are most active, ultimately limiting our understanding of how the deposits form and evolve and how they can be used to interpret long-term climate records. In this study, we use k-means clustering and random forest classification to identify and map a set of universal spectral endmembers across 167 high-resolution observations acquired during southern summer by the Compact Reconnaissance Imaging Spectrometer for Mars. The 21 endmembers show distinct combinations and strengths of key infrared absorption features reflecting diverse mixtures of CO2 ice, H2O ice, and dust. The resulting compositional framework can be used to characterize the nature of both seasonal CO2 frost and the residual ices it overlies across a variety of terrains. Following the large dust event of Mars Year 28, the residual CO2-ice deposits (RCD) were covered by an unusually thick or long-lived deposit of seasonal frost. Within the RCD, low-albedo material around erosional features display H2O ice absorptions consistent with exposures around the outer margins of the RCD. These peripheral water-ice deposits show unexpected variation in CO2 ice and dust content. Most notably, regions within several km of the edge of the RCD display spectral contributions from CO2 ice even after seasonal frost has been removed. These results can inform investigations focused on the dynamics of seasonal CO2 deposition, the development of erosional morphologies, and the creation of climate records in south polar stratigraphy.

Automated summary

In this study, spectral data and machine learning algorithms were used to classify and quantitatively analyze the ice deposits in the south polar region of Mars. Unexpected results were discovered based on the study of seasonal CO2 frost and residual ice, providing important clues for understanding climate change and geomorphological evolution in the south polar region of Mars.