Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p54c..07b&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P54C-07
Other
[5415] Planetary Sciences: Solid Surface Planets / Erosion And Weathering, [5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes
Scientific paper
Radar images from the Cassini spacecraft reveal closed, smooth and flat depressions above northern and southern latitudes of 60° on Titan, Saturn’s largest moon. These depressions have been interpreted as lakes of liquid hydro-carbons and dissolved nitrogen, resting on the icy crust that covers this moon. The depressions include large (over 100,000 square kilometers) seas with dendritic or poorly defined contours, small (1-10 km wide) circular steep-sided depressions, and medium-sized (20-50 km wide) depressions, the contours of which are composed of adjacent circular segments. Some depressions are completely filled with radar-dark material, while others are partially filled and some are empty. Most of these depressions lie in flat plains. By comparison with a terrestrial analogue located in the Etosha Basin (Namibia), we introduce here a dissolution-precipitation model for the formation of these lakes at the expense of a superficial soluble layer. The Etosha Basin is a flat sedimentary basin located at the western border of the Kalahari desert. The climate is semi-arid, with an average annual precipitation rate of 400 mm/yr and an average annual potential evaporation rate of 2200 mm/yr. Sediments in the basin include clays and silts; they are covered by a layer of soluble calcrete a few meters in thickness. The calcrete has formed by precipitation, in the subsurface, of calcium carbonate dissolved in groundwater. Precipitation of calcium carbonate from groundwater is due to the average annual dominance of groundwater evaporation over precipitation. The calcrete layer is dotted with dozens of so-called pans: these are closed, steep-sided, flat and smooth depressions, 1 to 200 km wide and a few meters deep. Relict boulders of calcrete rest on the silty, clayey and evaporitic floors of the pans and provide evidence that the pans grow by radial regressive dissolution of the calcrete layer. By comparison with the development of pans at the expense of the calcrete layer of Etosha, we infer that the small and medium-sized lakes of Titan grow by regressive radial dissolution, during flooding episodes associated with rainstorms, of a superficial soluble layer. The formation of this layer can be explained, as for the superficial calcrete layer of Namibia, by precipitation at or near the topographic surface of non-volatile materials, during evapo-ration after rainstorms of liquids accumulated in the ground.
Bourgeois Olivier
Cornet Thomas
Fleurant C.
Le Mouélic Stéphane
Lopez T.
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