Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0419w&link_type=abstract
American Astronomical Society, DPS meeting #28, #04.19; Bulletin of the American Astronomical Society, Vol. 28, p.1074
Astronomy and Astrophysics
Astronomy
Scientific paper
Europa, on the basis of its spectral characteristics and its apparently young surface age, is likely to be at least partially resurfaced by liquid water volcanic processes although convincing evidence for lava flow morphology in Voyager data has not previously been found. We examine a candidate feature and compare it with theoretical predictions for the ascent and eruption of water magma on Europa, outlining a range of conditions under which waterice flows could be erupted to the surface. Thrace Macula (45(o) S, 171(o) W) is a dark lobate feature extending NNW to SSE for a distance of about 220 km. Its width varies from 25-60 km, and its margins are lobate at a scale of 5-10 km. Three dark lobes extend away from a central region for distances of 40, 50, and 160 km. The 160 km lobe appears to follow local topographic features, producing lobate margins at subdued structures, broadening locally parallel to structural trends, and terminating against a gray band. Ascent of H2O magma through a less dense crust means that sustained effusive eruptions are very difficult to produce if a globally continuous liquid water (or salt-water) layer exists. We thus require magma reservoirs sufficiently localized that excess pressure can be built up, implying that sources are surrounded by relatively solid material. Given this magma source setting, modeling calculations show that flow lobes with the above geometries and thicknesses on the order of 10 m could be formed in water eruptions on Europa involving discharge rates of \ 2 x 105 m(3) /s through dikes with widths in the range of 5-10 m. These discharge rates (about three times larger than those of terrestrial flood basalts) should not be unusual for water eruptions on Europa under these conditions. The lack of abundant similar dark flows could be due to brightening by surface frosts with time, or to the possibility that conditions for flow formation (nearly solid ice crust) evolved only in the latter part of Europan history.
Head James
Pappalardo Robert
Wilson Leslie
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