Other
Scientific paper
Dec 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mst..........1e&link_type=abstract
M.S. Thesis, Arizona State University, Tempe, Arizona, United States, 196 p.
Other
Mars, Sand, Eolian, Aeolian, Intracrater Splotch, Dunes
Scientific paper
Dark features on the floors of craters (>/= 25 km in diameter) are common on the surface of Mars. Previous investigations indicated that they are related to aeolian sedimentary processes, and most are probably made up of unconsolidated, sand-sized material, with little incorporated dust or rocks. The highest quality and resolution Mariner 9 and Viking orbiter photographs and Viking Infrared Thermal Mapper (IRTM) data were analyzed in order to provide new information concerning the properties of these features. This study shows that the average particle sizes of martian dunes (inferred from the relationship between thermal conductivity and particle size at martian atmospheric pressures) are typically more coarse than terrestrial dune sands. For example, dunes in Proctor Crater (48°S, 330°W) have an effective particle size of approximately 500 microns, while typical terrestrial sand dunes have an average particle size of about 300 microns. The mean effective particle size for all of the dark intracrater features examined in this study was estimated to be 700 microns (+/- 40%). This study also reveals that there are regional groupings of dark intracrater features with similar effective particle sizes. There is a different mean effective particle size for each region, with a relatively narrow range of variation among individual dark features in the regions. The effective particle sizes of dark intracrater features in these regions range from very fine sands (~80 microns) in Northern Arabia to very coarse sand and granules (~2500 microns) in the Margaritifer Sinus region. Regional differences in the effective particle size likely results from differences in wind regimes; for example, in the region south of Margaritifer Sinus near Holden Crater, strong winds may winnow out finer sands, while in regions with relatively weak winds, such as Northern Arabia, finer materials are less easily removed. Regional differences also result from differences in the morphology of aeolian depositional forms (e.g., dunes) that occur on some dark deposits. For example, in Hellespontus there are thick dune fields with an effective particle size in the medium to coarse sand range, while in Oxia Palus the effective particle size is higher, resulting from the combined effects of small barchan dunes and a coarser interdune surface. To some extent, the nature of the dune forms are also related to regional wind regimes. Dark intracrater features are also ideally suited for determination of compositional properties using thermal emission data, because relative to other surfaces on Mars, they are free of dust and rocks which would alter their emissivity characteristics. The IRTM-derived thermal emissivity spectra of several dark intracrater deposits indicate that they are probably composed mostly of mafic rather than silicic or carbonate materials.
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