DIURNAL AND SEASONAL CO2 ICE AT KAISER CRATER, MARS

At the Kaiser crater dune field on Mars (46.9°S, 19.6°E, ~800 m MOLA elevation), repeat optical imagery has established a 12-Mars-year timeseries for monitoring local seasonal features, events, and processes. We use thermal models and mission data to characterize diurnal and seasonal CO₂ frost-driven activity and explore whether diurnal frost may be an agent of geomorphic change and how short- and longer-term frost deposits affect dune gully morphology. At this latitude, the landscape is not part of the areally continuous seasonal southern CO₂ ice cap; TES climatology confirms this. Seasonal CO₂ deposits are patchy and discontinuous and depend on local topography and insolation. Nighttime TES and THEMIS observations indicate diurnal CO₂ ice on the dune field, and CRISM full resolution images indicate the presence of CO₂ ice on southwestern steep slopes during cold-season midafternoons. We assess diurnal and seasonal CO₂ ice-driven processes on two areas of the dune field associated with 1 m/px digital terrain models. Multitemporal image and data analyses and thermal modeling for Kaiser crater dunes reveal interactions between seasonal insolation, sand and dust, and condensed CO₂, which produce phase transitions and trigger gravitational mass wasting.

We are testing the hypothesis that Insolation-Induced Basal Sublimation (IIBS) is directly or indirectly the cause of many seasonal features and events observed on frost-affected dune fields. We propose that diffuse, scattered insolation may be sufficient to induce Keiffer jets due to evidence indicating onset when solar elevation is at its annual minimum and suggest that remote-sensing-derived CO₂ ice secondary permeability (i.e., post-depositional permeability due to ice fracturing, as observed in many HiRISE images) estimates are plausible for Mars. We estimate the secondary permeability of CO₂ ice by combining Darcy’s law, the ideal gas law, & Clausius-Clapeyron relationship. Gas flow (for a fixed permeability) varies linearly with the amount of insolation that converts ice to gas at the regolith/ice interface. Initial results suggest that the secondary permeability of seasonal CO₂ ice, caused by diurnally cycled, thermally and mechanically induced shock, ranges between 10⁻¹² and 10⁻¹¹ m² (or ~0.1 and 1 Darcy), consistent with semipermeable materials.