Recent aeolian erosion and deposition in the north polar plateau of Mars.

Abstract

Background: Planum Boreum, the north polar plateau of Mars, displays four extensive low-albedo regions covered with widespread se dimentary deposits that are thick enough to partly or completely suppress the signature of the residual water ice that forms the uppermost zone of the polar layered deposits. These sedi mentary deposits appear to have a source primarily in a buried sedimentary layer preferentially exposed along the wall s and floors of some polar troughs. The deposits extend and drape over circum-polar dunes. Method: The data analyses in this research were conducted with Geographic Information Systems (GIS) mapping tools. The followin g data sets have been used: (1) Mars Odyssey (MO) Thermal Emission Imaging System (THEMIS) summer north polar visibl e light mosaics at 18 m/pixel and 32 m /pixel, as well as 18 m/pixel visible multiband images (THEMI S mosaic provided by P.H. Christensen and the THEMIS Team, Arizona State U.), (2) Mars Express (MEX) High Resolution Stereo Camera (HRSC) images at 10 m/pixel, (3) Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) narrow-angle (NA; >1.4 m/pixel) and a wide-angle image mosaic, 64 pixels/degree, (4) Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) camera images at resolutions that range from 31.8 cm/pixel (with 1 x 1 binning) to 63.5 cm/pixel (with 2 x 2 binning), (5) MGS Mars Orbiter Laser Altimeter (MOLA) 512 pixels/degree digital elevation models, and (6) MEX OMEGA Vis/IR imaging spectrometer. False color maps have been derived fro m OMEGA data in which all three color planes are proportional to albedo (0.1: level 0, 0.45: level 255) . The red plane scales inversely with the fraction of the area covered by ice, derived from the band stre ngth at 1.5 ?m (factor of 0 for 30% fractional ice coverage within the pixel, factor of 1 for ice-free pixels). The H 2 O ice spectral signatures have been observed by OMEGA in November 2004, during early northern summer (Ls 109? to 114?). The incidence at the time of observations was nearly optimal for such latitude regions (57.6?). Sampling on the ground was 1.7 to 2 km. Conclusion: The most recent history of the north pola r plateau of Mars includes highly dynamic sedimentary processes involving large-scale wind-d riven mass transfer from Planum Boreum towards its periphery. The proposed polar processes involved: (I) retreat along undulations within upper layered deposits (ULD), thereby exposing underlying dark sedimentary deposi ts, (II) mobilization of these deposits to form extensive dark mantles, which are water-ice free and that terminate in circum-polar terrains, and (III) complete removal of these depo sits leading to the exhu mation of pre-existing troughs