Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p22a..07h&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P22A-07
Mathematics
Logic
[1836] Hydrology / Hydrological Cycles And Budgets, [5419] Planetary Sciences: Solid Surface Planets / Hydrology And Fluvial Processes, [5462] Planetary Sciences: Solid Surface Planets / Polar Regions, [6281] Planetary Sciences: Solar System Objects / Titan
Scientific paper
Observing seasonal change in Titan's lakes and seas is considered one of the primary objectives of the Cassini Solstice Mission. Synthetic Aperture Radar (RADAR) images of the south polar region, acquired during southern summer, show lacustrine features which disappear between observations and a recession in the shorelines of Ontario Lacus. Both of these observations are consistent with an average one-meter-per-year liquid loss rate occurring between southern summer solstice and southern autumnal equinox. Repeat SAR images in the north, however, have shown no unambiguous changes in liquid level during northern winter. While the northern shoreline of Kraken Mare has exhibited backscatter variation that cannot be explained by geometric effects alone, the spatial variation of the observed changes suggest explanations other than varying liquid depth. These observations represent active hydrocarbon transport in Titan’s methane cycle. Lacustrine features that show no evidence for change between repeat SAR observations in the south polar region include filled lakes in the vicinity of the pole and dark areas, morphologically similar to terrestrial med flats, found near (150°E,80°S) and (0°E,75°S). Limited topography from SAR Topo measurements suggests these features are located in the lowest elevations of the south polar region. When referenced to estimates of Titan’s geoid, these areas have comparable elevations to the north polar mare shorelines. Ephemeral lacustrine features are located in the vicinity of SAR Topo measurements which are a few hundred meters above the lowest points in the south. The one-meter-per-year liquid loss rates estimated for both Ontario Lacus and transient southern lakes suggest a high methane concentration, as ethane and other hydrocarbons are stable over seasonal timescales. When coupled to the observation that large sections of Ontario Lacus are transparent to the radar, these loss rates suggest a significant seasonal variation in liquid composition. The two-way skin depth for the near-shore liquid in Ontario Lacus is approximately one meter, as measured by the exponential falloff of near-shore backscatter and referenced to radar altimetry tracks leading up to the shoreline. In areas where the RADAR can see through Ontario’s liquid layer, which includes almost the entire lake when considering real-aperture data, this implies a liquid depth of less than ten meters. Thus, removal of four meters of methane between 2005 and 2009 represents a significant fraction of the total liquid volume. These observations are consistent with recent GCM simulations, which suggest that the methane content of south polar lakes is completely depleted by the end of southern summer.
Aharonson Oded
Cassini RADAR Team
Elachi Ch.
Hayes Alexander G.
Kirk Randolph L.
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