Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) south polar mapping: First Mars year of observations

Abstract

We report on mapping of the south polar region of Mars using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument. Our observations have led to the following discoveries: (1) Water ice is present in the form of pole‐circling clouds originating from the circum‐Hellas region, beginning prior to Ls = 162 and diminishing markedly at Ls = 200–204. (2) It has previously been inferred by thermal infrared observations by Titus et al. (2003) and CO2‐H2O mixture spectral models by Langevin et al. (2007) that surface water ice was present in the cryptic region in the final stages of sublimation. The high resolution of CRISM has revealed regions where only water ice is present (not a CO2‐H2O ice mixture). This water ice disappears completely by Ls = 252 and may be the source of water vapor observed by CRISM in southern latitudes between Ls = 240–260 by M. Smith et al. (2009). (3) We have estimated surface CO2 ice grain size distributions for the South Pole Residual Cap (SPRC) and the seasonal CO2 ice cap that covers it throughout summer spring and summer. Our analysis suggests that grain sizes peak at Ls = 191–199 with an apparent grain size of ∼7 ± 1 cm. By the end of the summer period our analysis demonstrates minimum apparent grain sizes of ∼5 ± 1 mm predominate in the SPRC. (4) Fine‐grained CO2 ice condenses from Ls = 0–40 and extends symmetrically away from the geographic pole, extending beyond 80°S by Ls = 4–10. No evidence for unusual CO2 depositional processes in the cryptic region is observed up to Ls = 16.