Other
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........28b&link_type=abstract
PhD Dissertation, California Inst. of Tech. Pasadena, CA United States
Other
12
Mars (Planet), Mercury (Planet), Planetary Surfaces, Polarization Characteristics, Ice, Radar Cross Sections, Carbon Dioxide, Volcanoes, Structural Basins, Polar Regions
Scientific paper
Observations have been made using the combined VLA/Goldstone radar instrument at 3.5-cm. This technique has provided the first unambiguous radar cross section maps of Mars and Mercury at any wavelength. The most interesting structures probed by us on Mercury were features near and including the north and south poles. The polarization characteristics and signal strength indicate that ices exist in some quantity in the polar regions of Mercury. These ices probably exist in permanently shaded areas at high latitudes. We also found several large, quasi-circular regions on the surface of Mercury which have anomalously high radar cross sections. The Caloris basin shows no such anomaly, indicating that these large structures are probably not large impact basins. Our Mars experiments were the first to identify an unusually high cross section feature at the south pole, which is undoubtedly due to the ice of the residual cap. There is no such feature at the north pole, which we think is caused by some combination of three effects: (1) a fundamental difference in the structure and/or composition of the two residual caps, (2) the seasonal CO2 cap which was present during the north polar experiments absorbed enough of the incoming radar energy to obscure the north residual cap, and (3) the north polar regions were imaged with slightly poorer geometry. Many other regions with anomalous cross sections were found on the surface of Mars. The large volcanic provinces of Tharsis and Elysium have very high cross sections associated with them. These are most probably a result of the extremely rough surfaces of the large volcanoes and their associated flows. One of the most intriguing features in the Mars data set is a region which extends west from Tharsis for over 2000 km. This region displays no detectable cross section, prompting us to name it 'Stealth'. The surface and near surface must be composed of very underdense material, with an absence of volume scatterers (rocks). The proximity of Stealth to Tharsis suggests that it may be comprised in part of pyroclastic materials which were blown westward after eruptions from the large shield volcanoes.
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