ICE SUBLIMATION AND RHEOLOGY - IMPLICATIONS FOR THE MARTIAN POLAR LAYERED DEPOSITS

It has been suggested that the Martian polar layered deposits are composed largely of water ice. If true, then sublimation and deformation creep of the ice are important processes. Simple models indicate that sublimation will occur at a rate inconsistent with current estimates of the deposit's age and Viking observations of the atmospheric water abundance, suggesting that when considering the formation, evolution, and structure of the deposits, one must include a mechanism by which sublimation is inhibited. A surface layer of dust seems the most likely possibility. Additionally, over the age of the deposits, flows of at least 1 km are expected. At Viking resolution (≥150 m) no obvious flow features are observed. Assuming that Martian features would be similar to those that occur on the Earth, this limits the maximum flow rates possible and suggest the deposits need to be more than 90% ice or less than about 40% ice by volume. The Mars Observer spacecraft will be able to constrain the ice abundance further by both searching for flow features and clarifying the nature of the deposit's surface and near surface. © 1990.