SHARAD: EARLY RESULTS FROM THE SOUNDING RADAR ON THE MARS RECONNAISSANCE ORBITER

SHARAD (SHAllow RADar) is a sounding radar provided by the Italian Space Agency as a Facility Instrument on the Mars Reconnaissance Orbiter mission. Its 20-MHz center frequency and 10-MHz bandwidth complements the lower frequency, relatively narrower bandwidth capability of the MARSIS sounding radar aboard the Mars Express Orbiter. SHARAD has been in operation since November, 2006, and has already acquired a large volume of data. The radar is particularly good at mapping the internal, fine-scale layering in the deposits at the North and South Poles of Mars. At the North Pole, SHARAD paints a three-dimensional picture of the stratigraphy mapped (by visible imaging) in canyon exposures on the periphery of the cap. Differences in elevation across the cap are seen to be caused by a relatively constant thickness ice-rich layered unit resting on a more coarsely layered basal deposit that is of variable thickness and likely contains a sand component. In both the North and South Polar regions, SHARAD has mapped angular unconformities, possible faulting, and possible folding. Also detected are layered ice deposits on the periphery of the caps. SHARAD has also mapped subsurface reflectors at mid- and low-latitudes on Mars. In Amazonis Planitia, SHARAD has mapped an interface at 40-90 m depth along the margin of a high 12.6-cm backscatter area as mapped by Earth-based radar and interpreted to be a lava flow. The best explanation for subsurface reflections across Amazonis is that they arise from the interface between lava flows and underlying sediments. There is little support for a near-surface ice-rich sediment layer in Amazonis Planitia. Similarly, in the southern Elysium region of Mars, a vast area (~500,000 km²) contains deposits that are transparent to SHARAD radar waves and have a depth of ~70 meters as observed by SHARAD. Other observations, from visible images and spectrometers, indicate that these deposits are of volcanic origin. Further to the west, in the area considered by some workers as the "Frozen Sea" (~5 °N-150 °E) SHARAD does not detect any evidence of ice. Elsewhere in the northern lowlands of Mars, subsurface reflectors have been detected and the analyses of these results are ongoing.