Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.p12e..09h&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #P12E-09
Other
1
5410 Composition, 5462 Polar Regions, 5464 Remote Sensing, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
Quantitative measurement of the transport of water and dust into the winter polar regions of Mars has generally been limited to scaling arguments, which propose that water and dust are incorporated into the seasonal polar cap in proportion to their average atmospheric mixing ratios. Spectral analyses of very limited areas have determined that both constituents occur at or below the 0.1% level in the seasonal caps. I have looked at one revolution of the Mars Global Surveyor to investigate the distribution of water and dust in the seasonal cap. Approximately 80% of the data from this revolution observes the mid-winter northern polar cap, which covers the surface to <60° N, and is predominantly within the polar night. The surface composition and temperature are determined through analysis of 6-50 μ m spectra from the Thermal Emission Spectrometer. The primary polar cap surface constituent is CO2 ice, which dominates the spectral variation in the 20-50 μ m range by variations of its grain size and purity. The surface model includes spatial mixtures of CO2 ice, intimately mixed with water ice and dust, and another surface material at a different temperature. This surface model, along with a simple water ice cloud model, is fit to individual spectra in the sequence. The results reveal CO2 grain radii ranging from ~100 μ m in isolated areas to 1-5 mm in more widespread regions. The water ice content of the CO2 varies from none to ~0.1% by mass, with a clear increase towards the periphery. The dust content is typically a few 0.1% by mass. The fringes of the polar cap have more dust and water ice, and the CO2 coverage becomes patchy, with (apparently diurnal) warmer water snow filling the gaps on the night side, and warmer bare soil on the day side. The water ice mixed in the CO2 and the water ice in the patches must have a ~2 μ m particle size to affect the spectra in the observed way. This agrees with the uniform particle sizes observed for water ice in the Martian atmosphere. This analysis and that of other revolutions can provide essential information on the transport of water and dust into the polar regions in the Martian winter.
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