THE GLACIAL ORIGIN OF MARTIAN LANDFORM ASSEMBLAGES

One of the many innovative projects that An Yin was working on before his death concerned the hypothesis that a large fraction of the surface of Mars may have been extensively glaciated. Present-day Mars hosts ice sheets at the north and south poles as well as debris-covered mountain glaciers in mid-latitude regions. Despite the ubiquity of ice on present-day Mars, notion that thick ice deposits may have once covered most of the planet is not universally accepted within the Mars geology community. Much attention has been paid to Mars’ surface fluvial history, and its implications for past Martian life. However, as our observations and understanding of terrestrial glacial processes and glacial environments has matured, it has become clear that a good fraction of Martian geomorphic features that have been conventionally attributed to the presence of surface liquid water during a warmer and wetter paleoclimate, could have also formed in sub-glacial environments. In fact, subglacial fluvial processes are much more easily reconciled with the results of Mars paleo climate models. On Earth, sub-glacial environments are not well preserved in the long-term geologic record, but the same may not necessarily be true on Mars. A key element of An Yin’s planetary-scale glacial hypotheses is that planets that experience irreversible climate degradation inevitably transition through a glacial period. While potentially brief in duration, this terminal glacial phase could potentially accomplish a significant amount of geomorphic work. If followed by a quiescent post-glacial era with low erosion rates, then the resulting glacial landforms could remain preserved on the surface for billions of years. It took many decades to convince geologists that glacial processes were responsible for a wide range of non-polar terrestrial landform assemblages. Further studies of glacial landscapes on Mars have the potential to provide a valuable record of the planet’s transition from a habitable to an unhabitable surface environment.