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Transient surface liquid in Titan’s polar regions from Cassini |
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| Authors: | AG Hayes O Aharonson RL Kirk LC Wye EP Turtle G Mitri ER Stofan C Elachi the Cassini RADAR Team |
| Institution: | a Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States b Dipartimento di Fisica, Università degli Studi di Roma “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Roma, Italy c Astrogeology Team, United Stated Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001, United States d Applied Physics Laboratory, John Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723, United States e Electrical Engineering, Stanford University, 350 Serra Mall, Stanford, CA 94305, United States f Laboratoire d’Astrophysique de Bordeaux, Université de Bordeaux, UMR5084, Floirac, France g Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, United States h Proxemy Research, 20528 Farcroft Lane, Gaithersburg, MD 20882, United States |
| Abstract: | Cassini RADAR images of Titan’s south polar region acquired during southern summer contain lake features which disappear between observations. These features show a tenfold increases in backscatter cross-section between images acquired one year apart, which is inconsistent with common scattering models without invoking temporal variability. The morphologic boundaries are transient, further supporting changes in lake level. These observations are consistent with the exposure of diffusely scattering lakebeds that were previously hidden by an attenuating liquid medium. We use a two-layer model to explain backscatter variations and estimate a drop in liquid depth of approximately 1-m-per-year. On larger scales, we observe shoreline recession between ISS and RADAR images of Ontario Lacus, the largest lake in Titan’s south polar region. The recession, occurring between June 2005 and July 2009, is inversely proportional to slopes estimated from altimetric profiles and the exponential decay of near-shore backscatter, consistent with a uniform reduction of 4 ± 1.3 m in lake depth.Of the potential explanations for observed surface changes, we favor evaporation and infiltration. The disappearance of dark features and the recession of Ontario’s shoreline represents volatile transport in an active methane-based hydrologic cycle. Observed loss rates are compared and shown to be consistent with available global circulation models. To date, no unambiguous changes in lake level have been observed between repeat images in the north polar region, although further investigation is warranted. These observations constrain volatile flux rates in Titan’s hydrologic system and demonstrate that the surface plays an active role in its evolution. Constraining these seasonal changes represents the first step toward our understanding of longer climate cycles that may determine liquid distribution on Titan over orbital time periods. |
| Keywords: | Titan Saturn Satellites Radar observations Infrared observations |
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