1. Analysis and mapping of Martian dunes and dune fields
lead: P. Allemand (LGL)
coll.: V. Langlois - A. Quiquerez (LGL), O. Bourgeois - S. Le Mouélic (LPGN)
Dunes composed of basaltic sand grains cover wide regions of the southern hemisphere of Mars. In addition, the largest dune field on Mars, which encircles the North Polar Cap, is composed of gypsum mixed with ice grains (Massé et al., 2010, 2012). These dune fields of the southern (LGL) and northern (LPGN) hemispheres of Mars will be mapped at high resolution in terms of geometry using the 6m resolution CTX images (MRO mission) and in terms of mineralogy using CRISM data (MRO mission). If available, HiRiSE images (MRO mission) which have spatial resolution from 0.25 to 1m will be also studied. Digital elevation models will be computed in favorable cases from CTX, MOC (MGS mission) or HiRiSE images. These data will be collected in GIS (Geographic Information Systems), one per dune field. Area covered by dune fields, volume of sand, directions of wind, topography, sand composition and thermal inertia at high resolution, and possible stratigraphic relationships between the various dunes will be mapped (see Gardin et al, 2011b). On some dunes, the orientation of layers defining their internal geometry will be included in the GIS (Gardin et al., 2010). The impact craters overlapping dunes, which are very rare, will be mapped in order to give an approximate age of the dune surfaces. These series of detailed GIS, performed at high resolution, will complete and improve the works of Hayward et al. (2007, 2010) or Gardin et al. (2011a). This database will furnish geometric and possibly cinematic parameters to the experimental researchers and modelers of dunes fields (see WP2 and WP3). This database of Martian dunes interpreted in terms of history of wind direction will be also compared to the results of Martian climate models (see Task 3.1).
2. Ice dunes on Mars
lead: O. Bourgeois (LPGN)
coll.: C. Herny (LPGN), S. Carpy (LPGN), S. Le Mouélic (LPGN), S. Rodriguez (AIM)
The North Polar Cap of Mars is composed of giant ice dunes (Smith and Holt, 2010; Massé et al., 2012). The formation of these dunes is related, as it is in the Antarctic ice cap, to katabatic winds descending from the north polar high towards the margins of the polar cap. The internal structure of these giant dunes, as revealed by radar soundings, indicates that they grow and migrate upwind (Smith and Holt, 2010). It is still unclear however, whether these dunes form only by transportation of solid ice particles above the surface of the polar cap, or whether transportation of water vapor produced by sublimation of ice plays also a part in their formation. The link between the development of these dunes and Martian seasons is also unknown. We aim at clarifying these points by mapping blowing snow, water vapor and different varieties of ices (fresh snow, bounded snow grains, glazed ice, dry ice, wet ice, porous ice, compact ice) on the North Polar Cap over a full Martian year. To do this, we will use both radar data provided by the SHARAD instrument and orbital hyperspectral images provided by the OMEGA and CRISM instruments onboard Mars-Express and MRO respectively. These hyperspectral analyses will be constrained by natural spectra acquired on terrestrial ice dunes (Task 1.E.3). We will thus produce two kinds of maps for each season of a Martian year (which lasts for 2 terrestrial years): (1) maps of the surface of the ice cap, showing the location of various kinds of ices, corresponding to ice erosion and ice accumulation areas, and (2) maps of the atmosphere above the ice cap, showing transport of solid grains of ice by blowing snow and transport of water vapor by volatilization/condensation of ice. These maps will be compared with the location of the giant ice dunes, in order to infer the physical processes (solid transportation vs. vapor transportation) that lie behind their formation. These observational data will also be compared with maps of local winds provided by climate models (Task 3.1) and used to constrain numerical models of the development of ice dunes in relation with atmospheric circulation above the boreal regions of Mars (Task 3.3).