High-latitude Recent Surface Mantle On Mars: New Results From Mola and Moc

The latitudinal trend of MGS-MOLA-derived kilometer-scale surface roughness on Mars has been interpreted as the presence of a geologically young several-meter-thick mantle at high-latitudes, which has a specific ten-meter-scale "basketball" surface pattern in MGS MOC images (Kreslavsky and Head, J. Geophys. Res., 105, 26695- 26711, 2000). A specific dissected pattern seen in MOC images in narrow mid-latitude zones has been interpreted as evidence for ongoing desiccation of ground ice (Mus- tard et al., Nature, 412, 411-414, 2001). This pattern can be interpreted as peripheral degrading part of the high-latitude mantle. We present new maps of MOLA-derived statistical characteristics of kilometer-scale topographic pattern showing the global distribution of the mantle and its distal dissected parts in the northern lowlands. We use a selection of high-quality MOC images of the northern lowlands to characterize the variability of the small-scale morphology of the mantle deposits and their strati- graphic relationship with other young features around the polar cap: dunes of dif- ferent types, dune fields, layered terrains, Chasma Boreale-related deposits, etc. We discuss possible ice content in the mantle, possible mechanisms of mantle formation and degradation, and possible time scales of these processes. Formation and degrada- tion of the mantle could follow obliquity oscillations at 0.05 Myr time scale. It is also possible that the mantle is more inert and its formation and degradation is controlled by 2-5-Myr-scale chaotic obliquity wander.