Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p33a1277w&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P33A-1277
Mathematics
Logic
[6295] Planetary Sciences: Solar System Objects / Venus, [6969] Radio Science / Remote Sensing
Scientific paper
Radar observations of Venus collected by NASA’s Magellan mission show unusually high radar reflectivity from the Maxwell Montes, a large massif up to 11.4 km above the lowlands, and from other high mountain ranges (Pettengill et al. Science 272, 1628-1632, 1996). The increased reflectivity suggests a surface layer with high electric conductivity, but the nature of such a surface layer remains poorly understood. The radar reflectivity of gabbro was measured in the laboratory at an RF frequency of 1.2 GHz. One end of a block of gabbro was placed in an electric furnace and heated to 600°C. Electron vacancy defects present in the oxygen anion sublattice of silicate minerals, e.g. O- in a matrix of O2-, become thermally activated in two steps, at 300°C and more massively at 430°C. Once activated and mobilized, the positive charge carriers flow out of the heated subvolume and into the colder portion of the rock. They accumulate at the cooler surface, giving rise to a surface/subsurface layer with enhanced electrical conductivity. The radar reflectivity from the cold end began to increase when the hot end reached 300°C. It increased upon further heating, up to 5% above baseline at 25°C. These data suggest that the high radar reflectivity observed at high elevations on Venus may not be caused by a chemical surface layer such as a conductive sulfide deposit. Rather, it is due to an electrically conductive surface layer formed by electronic charge carriers, which are activated in the hotter lowland regions and diffuse to the cooler mountain tops. Further studies of heat-activated charge carriers in rocks and their drift in large-scale temperature gradients will deepen our understanding of physical and geological processes on Venus.
Cyr G. G.
Dahlgren R.
Freund Friedemann T.
Keefner J.
Tsoflias Georgios P.
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