Martian airborne dust: How it forms and evolves. Near-surface versus high-altitude properties. W. Goetz*, L. Drube, M.H. Hecht, S.F. Hviid, K. Leer, M.B. Madsen, D. Parrat, W.T. Pike, U. Staufer, H. Sykulska, and S. Vijendran. *Corresponding author: Max Planck Institute for Solar System Research (MPS), Max Planck Strasse 2, 37191 Katlenburg-Lindau, Germany, phone: + 49 5556 979463, firstname.lastname@example.org. PRESENTING AUTHOR: Goetz, W. There are two types of data sets that are particularly useful for analysis of the Martian airborne dust: (a) In-situ data (APXS, Mössbauer, VIS/NIR reflectance, microscopy) of the dust fraction that is accumulated on permanent magnets onboard rovers and landed spacecrafts (Mars Pathfinder, Mars Exploration Rovers (MER), Phoenix), and (b) remote sensing data (e.g. Mars Global Surveyor (MGS), Hubble Space Telescope (HST)) that are acquired during global dust storms. Merging all data sets and inferring a consistent picture of the formation and evolution of the Martian dust remains a very important task and will shed much light on the evolution of the planet. MER data and remote sensing data (MGS, HST) suggest that the airborne dust is an inhomogeneous mixture containing (at least) two subsets of particles (labeled 1 and 2). Subset 1 is highly weathered and consists of bright, weakly magnetic, micron-sized particles that are rich in silicon, calcium, sulfur, and chlorine [Madsen et al., 2009]. The particles in this subset may be dominated by weathered basaltic precursor minerals (including plagioclases [Hamilton et al., 2005]) stained by a poorly crystalline ferric oxide phase [Morris et al., 2006]. They tend to make up the small part of the size distribution of airborne particles, can easily be transported laterally/vertically and are found at all altitudes (including high altitudes) as a result of their low weight and density. Subset 2 is little altered and consists of darker, more strongly magnetic, coarse-grained (silt- to sand-sized) lithic fragments enriched in titanium-chromium-bearing magnetite [Goetz et al., 2005, 2008; Madsen et al., 2009]. These particles are mostly found near the surface (say at altitudes up to 10 m) as a result of their larger size, weight and density and make up a saltation load that drives the slow wind abrasion on the surface of the planet. The details of the weathering processes leading to subset 1 are largely unknown, although analysis of the particle size distribution of Phoenix dust may provide a hint.
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