Abstract
Background: Planum Boreum, the north polar plateau of Mars, displays four extensive low-albedo regions covered with widespread sedimentary 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 sedimentary deposits appear to have a source primarily in a buried sedimentary layer preferentially exposed along the walls 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 following data sets have been used: (1) Mars Odyssey (MO) Thermal Emission Imaging System (THEMIS) summer north polar visible light mosaics at 18 m/pixel and 32 m /pixel, as well as 18 m/pixel visible multiband images (THEMIS 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 from 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 strength at 1.5 μm (factor of 0 for 30% fractional ice coverage within the pixel, factor of 1 for ice-free pixels). The H2O 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 polar plateau of Mars includes highly dynamic sedimentary processes involving large-scale wind-driven 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 deposits, (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 deposits leading to the exhumation of pre-existing
Highlights
The polar regions of both Earth and Mars have volatile-rich deposits, the histories of accumulation of which are thought to have been predominantly controlled by their respective climatic histories
Christensen and the Thermal Emission Imaging System (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 to 63.5 cm/pixel, (5) MGS Mars Orbiter Laser Altimeter (MOLA) 512 pixels/degree digital elevation models, and (6) MEX OMEGA Vis/IR imaging spectrometer
The fact that (1) north polar veneers (Vn in Figures 12 and 14) commonly extend from dark interior deposits within polar troughs, (2) these two surficial deposits are free of water-ice, (3) there is a correlation between the degree of mantling by surface veneers and the size of the dark interior deposits within polar troughs (e.g., Figures 7b and 7c), and (4) some polar trough surfaces are free of water-ice but have adjacent plateau surfaces that contain modest amounts of water-ice, which is consistent with incipient veneer mantling of the residual ice (Figures 1b and 2b), suggest that ID materials comprise the veneers’ primary source regions
Summary
The polar regions of both Earth and Mars have volatile-rich deposits, the histories of accumulation of which are thought to have been predominantly controlled by their respective climatic histories. The underlying layers are darker and make up a tens-of-meter-thick sequence of relatively high-albedo upper layered deposits (ULD), which appear to lack unconformities. Planum Boreum, the north polar plateau of Mars, displays four extensive low-albedo regions covered with widespread sedimentary 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 sedimentary deposits appear to have a source primarily in a buried sedimentary layer preferentially exposed along the walls and floors of some polar troughs.
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