MRO’s HiRISE COVERAGE OF FLUVIAL LANDFORMS ON MARS DURING ITS PRIMARY

Introduction: The Mars Reconnaissance Orbiter's High-Resolution Imaging Science Experiment completed its primary science phase (lasting one Mars year) in November 2008. By the end of the primary science phase, the HiRISE camera completed 9549 observations for a total of approximately 8 Terabytes of data. These observations cover an area close to 938,000 km 2 or approximately 0.6% of the surface of Mars. This area is nearly as large as the area of Egypt or the combined areas of California, Oregeon and Ne-vada. During this time HiRISE targeted suggestions from 16 different science themes in addition to suggestions for future landing sites, and student suggestions. Of the completed observations, approximately 840 observations of valleys (e.g., large valley systems, valley networks, longitudinal valleys and slope valleys) approximately 424 observations of channels, and approximately 644 observations of gullies have been obtained (Figure 1). Outflow Channels: Several hundred images of the outflow channels on Mars have been collected to date from HiRISE, as well as coordinated images with CTX and CRISM. Depositional features, such as slackwater deposits and small bedforms that are expected to be visible at the resolution of HiRISE have not yet been observed, largely due to post-fluvial modification of the channels. Many of the channels have been subsequently covered by a thin layer of lava, ash, dust, or lineated valley fill. Although altered slightly by later aeolian modification , Ares Valles and Kasei Valles preserve much of the original fluvial erosional forms, particularly cataracts and longitudinal grooves that can be used to infer the mechanics of the flow. Cataracts, steep knickpoints in the large outflow channels, were once large waterfalls on the Martian surface. These have been observed in all of the larger outflow systems, including Kasai, Athabasca, Mangala, and Reull Valles. High resolution imaging shows that most of the cataract systems that we have imaged so far appear to have multiple generations of erosion, with smaller sub-channels within the cataract system [1]. Based on the length of the recession and the morphological evidence most of the large channels experienced multiple flooding events or pulses. Other erosional landforms are present as well in the outflow channels including flute casts, potholes, scour marks, scour pits and small, interior channels within the main channel system. The