Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p72a0491f&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P72A-0491
Other
5415 Erosion And Weathering, 5445 Meteorology (3346), 5464 Remote Sensing, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
The thermal inertia of Martian dunes has been studied in detail since the first thermal models were produced for Mars. In particular, the dunefield within Proctor Crater, located in the southern highlands in Noachis Terra, has been used as a basis for comparison between different models. Here, the sedimentary environment of the interior of Proctor Crater is described in detail using recently derived thermal inertias from the Thermal Emission Spectrometer (TES) [Jakosky et al., 2000; Mellon et al., 2000]. The warmest and clearest TES tracks produce an average thermal inertia of 277 +/- 17 J m-2 s-0.5 K-1, consistent with a grain size estimate of 740 +/- 170 μm. This estimate is in the range of coarse sand (e.g., 500-1000 μm), as expected for Martian dune sands. Furthermore, each TES track crossing the dunefield shows a steady decrease in thermal inertia to the south. This trend comes from differential cooling rates of the dune surfaces reflected in nighttime surface temperatures, rather than being an artifact produced by changes in albedo, air pressure, or elevation. This shift could be produced by a number of different processes, such as a spatial variation in mean grain size or dune cementation, or by a gradual shift in the percentage of interdune flats relative to dunes. Possible sources of this trend are discussed. The remainder of the crater floor shows an interesting patchwork of varying thermal inertias. Where small bright duneforms predominate (distinct from the large dark dunes that comprise the dunefield), effective thermal inertias are consistent with grains in the range of medium to coarse sand, the lowest values on the floor of Proctor Crater. However, the bright duneforms are probably not composed of loose sand grains, because in areas these bright duneforms appear partly degraded, suggesting some amount of cohesion. They are interpreted to be either stabilized dunes covered by some amount of dust that artificially lowers their thermal inertia, or granule ripples. Other places of the floor of Proctor Crater have thermal inertias consistent with gravel or indurated fine material. The lack of dust devil tracks and bright duneforms in these areas suggests that this is a windswept terrain, where all loose material has been deflated by the wind and the surface has been scoured, perhaps exposing a lower layer of material in Proctor Crater. A similarly high thermal inertia in a large deep deflationary pit on the crater floor suggests that such indurated terrains could comprise several sedimentary layers in the crater, now only revealed by erosive wind action. The thermal inertia of the floor of Proctor Crater indicates a terrain dominated by aeolian processes. Sand and dust deposition as well as deflation and abrasion have worked together to form and modify the surface of the crater floor. Additionally, for the first time, the change in thermal inertia across a Martian dunefield is investigated in order to understand its sedimentary history. Jakosky, B. M., et al., JGR, 105, 9643-9652, 2000.; Mellon, M. T., et al., Icarus, 148, 437-455, 2000.
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