Sounding Titan's Lakes and Seas: Bathymetry, Composition, and Role in the Hydrologic Cycle

Abstract : One of the most surprising discoveries of the Cassini Solstice Mission is the microwave transparency of Titan's lakes and seas. Coherent processing of altimetry echoes acquired over Ligeia Mare in May 2013 revealed bottom reflections and allowed construction of a bathymetric profile as well as an estimation of the liquid loss tangent. Following the successful detection of subsurface echoes at Ligeia, the RADAR team organized a campaign to acquire altimetry over the remaining Mare. Altimetry over Kraken and Punga Maria were obtained in August 2014 and January 2015, respectively, and also show detectable subsurface echoes. Using new analysis techniques, subsurface returns were also recovered from data acquired over Ontario Lacus in 2008. The final Titan flyby (T126, April 2017) will acquire altimetry over several of the smaller lakes in Titan's north, permitting comparative studies between the Mare and lakes. In this presentation, we will report on the latest results from this ongoing campaign.Assuming a ternary composition of CH4, C2H6, and N2, the best-fit loss tangent at Ligeia Mare is consistent with 71% CH4, 12% C2H6, and 17% N2 by volume. The best-fit loss tangent Ontario Lacus is consistent with 47% CH4, 40% C2H6, and 13% N2. The higher loss tangent at Ontario Lacus could result from an increased abundance of more involatile hydrocarbons and/or nitriles; these species could be concentrated as a consequence of orbitally-driven insolation cycles that may have slowly transported volatile components (methane/ ethane) to the north over the past several tens of millennia. Initial analysis of Kraken and Punga Maria suggest liquid absorptivity similar to Ligeia Mare. In total, the bathymetric results suggest that the total volume of Titan's lakes and seas is >70,000 km3. If this liquid were evenly spread across the surface it would be equivalent to a global ocean depth of 1 m. This is equivalent to 300 times the mass of Earth's proven natural gas reserves. Unlike Earth, where the total water content in the atmosphere (1.29x104 km3) is only a fraction of the surficial reservoir (1.35x109 km3), the moisture content in Titan's atmosphere is approximately seven times larger than the volume found in its lakes and seas.
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Submitted on : Monday, October 31, 2016 - 4:52:58 PM
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Alexander Hayes, Marco Mastrogiuseppe, Jonathan I. Lunine, Valerio Poggiali, Ralph Lorenz, et al.. Sounding Titan's Lakes and Seas: Bathymetry, Composition, and Role in the Hydrologic Cycle. DPS 48 / EPSC 11 (Division for Planetary Sciences and the European Planetary Science Congress), Oct 2016, Pasadena, United States. ⟨insu-01390112⟩

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