Martian airborne dust How it forms and evolves. Near-surface

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					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,
goetz@mps.mpg.de.

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.