Exploring Mars at sub-meter scales with MRO/HiRISE

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author McEwen, Alfred
Holding Date 08 October 2008

By 6 March 2008 the High Resolution Imaging Science Experiment (HiRISE) had acquired more than 5,675 images of Mars with 4,986 Gigapixels in the 3 PM mapping orbit of Mars Reconnaissance Orbiter (MRO), uniquely covering about 0.4 percent of the surface. The images have scales of 25-32 cm/pixel or are binned 2× or 4×, and the effective resolution can be considered equivalent to ~3 pixels. These images are helping to address a broad range of science issues. The high signal-to-noise ratio color data is proving quite valuable to reduce the ambiguities of monochromatic images; to correlate deposits and better define the stratigraphy; and to extend mineral identifications to the scale of outcrops. The properties of the Noachian crust are being revealed, with the identification of megabreccia and layered or massive strata where exposed in cross-section. The Noachian crust is largely indurated, perhaps by groundwater, and has different physical properties and mineralogy than the lunar terra crust. We suggest that the abundant megabreccia in clay-rich units near Nili Fossae supports the interpretation that this is impact ejecta from the Isidis basin.
There is new evidence for the roles of water in the most recent large (at least 1 km diameter) impact craters, which may have implications for present-day ice in the crust, Noachian fluvial landscape evolution, and the altered mineralogy of the ancient crust. The many channels emanating from the ejecta of Hale crater (125 × 150 km diameter) is especially striking. New observations and measurements are leading to improved understanding of active processes such as aeolian, impact, polar, and slope modification (gullies, creep, and mass wasting). Evidence for present-day outbreaks of groundwater creating bright gully deposits has not yet been confirmed by MRO, but observations of fractured mounds, if they form like terrestrial pingos, suggest that groundwater was recently present in the shallow subsurface in the middle latitudes. 513 stereo pairs have been completed, and we are producing meter-scale digital elevation models to address high-priority science questions.