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The particle size of Martian aeolian dunesThe effective particle size of unconsolidated materials on the Martian surface can be determined from thermal inertia, due to a pore size dependence of thermal conductivity at Martian atmospheric pressures. Because dunes consist of a narrow range of well-sorted, unconsolidated particles, they provide for a test of the relationship between particle size and thermal inertia calculated from midinfrared emission data for the Martian surface. Two independent approaches are used. First, thermal inertia data indicate that Martian dunes have an average particle size of about 500 +/-100 microns, or medium to coarse sand. Second, expected dune particle sizes are determined from grain trajectory calculations and the particle size transition from suspension to saltation. On earth, the transition occurs for a grain when the ratio of the terminal fall velocity to the wind friction speed, u*(t) is near unity; for grains at u*(t) this occurs at about 52 microns. Terrrestrial dune sands have a mean of 250 microns and are composed entirely of grains greater than 52 microns. The corresponding Martian transition grain size is about 210 microns, suggesting that Martian dunes should be significantly coarser than terrestrial dunes. Grain saltation path length as a function of particle size also shows that, under Martian conditions, larger grains than on earth will become suspended. Both approaches indicate that Martian dune sand should be coarser than terrestrial dune sand. These results closely match the grain sizes determined from thermal inertia models, providing the first direct test of the validity of these models for actual Martian surface materials.
Document ID
19920036136
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Edgett, Kenneth S.
(Arizona State Univ. Tempe, AZ, United States)
Christensen, Philip R.
(Arizona State University Tempe, United States)
Date Acquired
August 15, 2013
Publication Date
December 25, 1991
Publication Information
Publication: Journal of Geophysical Research
Volume: 96
ISSN: 0148-0227
Subject Category
Lunar And Planetary Exploration
Accession Number
92A18760
Funding Number(s)
CONTRACT_GRANT: NAGW-2289
CONTRACT_GRANT: NAGW-943
Distribution Limits
Public
Copyright
Other

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