SURPRISING GEOLOGIC PROCESSES OF MARS: EARTH-LIKE GEOMORPHOLOGIES MAY BE DECEIVING

Mars certainly appears Earth-like as seen in sub-meter resolution orbital images from MRO/HiRISE as well as from landers and rovers. But after more than 10 years of monitoring Mars from orbit, we have seen many surface changes from active processes, and some of these processes are very different from those producing similar-looking terrains on Earth. The terrains are also similar in 3D digital terrain models (DTMs); these same DTMs enable orthorectification of sets of images for change detection. The martian “gullies” or ravines form via processes that require seasonal CO₂ frost, as do the polar “spiders” (radiating troughs). These dry-ice driven processes do not occur naturally on Earth, yet produces some very familiar-looking landscapes like gullied slopes as well as bizarre landscapes like those with “spiders”. The recurring slope lineae (RSL) appear morphologically similar to water tracks in Antarctica, and even show the same seasonal behavior, but may form via very different processes (although this is still controversial). There are apparent ground slumps associated with some RSL, and they are also seasonal, but that seasonality is different from the RSL. Thermokarst terrains in the middle latitudes appear similar to terrestrial analogs according to some workers, but likely form via sublimation rather than melting of ice. Eolian dunes appear very Earth-like but are covered by smaller mini-dunes (often called ripples) that are not seen on Earth. Terrains indicative of other processes (volcanic, tectonic, impact, glacial, periglacial, and fluvial) often appear very similar to terrestrial analogs, but have not (yet) been observed to change. How safe, in general, are interpretations of martian geomorphology based on terrestrial analogs, especially when volatiles play a key role? This talk is also an excuse to show off the spectacular results from HiRISE over the past 11 years at Mars.