Mars south polar spring and summer behavior observed by TES: Seasonal cap evolution controlled by frost grain size

Thermal Emission Spectrometer (TES) observations of the recession phase of Mars' south polar cap are used to quantitatively map this recession in both thermal and visual appearance. Geographically nonuniform behavior interior to the cap is characterized by defining several small regions which exempl ify the range of behavior. For most of the cap, while temperatures remain n ear the CO2 frost point, albedos slowly increase with the seasonal rise of the Sun, then drop rapidly as frost patches disappear over a period of simi lar to 20 days. A "Cryptic" region remains dark and mottled throughout its cold period. TES observations are compared with first-order theoretical spe ctra of solid CO2 frost with admixtures of dust and H2O. The TES spectra in dicate that the Cryptic region has much larger grained solid CO2 than the r est of the cap and that the solid CO2 here may be in the form of a slab. Th e Mountains of Mitchel remain cold and bright well after other areas at com parable latitude, apparently as a result of unusually small size of the CO2 frost grains; we found little evidence for a significant presence of H2O. Although CO2 grain size may be the major difference between these regions, incorporated dust is also required to match the observations; a self-cleani ng process carries away the smaller dust grains. Comparisons with Viking ob servations indicate little difference in the seasonal cycle 12 Martian year s later. The observed radiation balance indicates CO2 sublimation budgets o f up to 1250 kg m(-2). Regional atmospheric dust is common; localized dust clouds are seen near the edge of the cap prior to the onset of a regional d ust storm and interior to the cap during the storm.