Frozen Hydrocarbon Ponds on Titan: Implications for Titan’s Lakes and Seas
Abstract
Cassini Imaging Science Subsystem (ISS) observations have detected widespread darkening of Titan’s surface believed to be the result of rainfall: in 2005 at Arrakis Planitia, near Titan’s south pole (Turtle et al., 2009, GRL 36, L02204), and in 2009 in Titan’s tropics (Turtle et al., 2011, Science 331, 1414-1417). Cassini Visual and Infrared Mapping Spectrometer (VIMS) and ISS observations revealed that, following the tropics storm, the albedo of the wetted surfaces increased, beyond even their original albedo, then slowly faded back to a pre-rain brightness over ~10 months (Barnes et al., 2013, Planet. Sci. 2, 1). Herein we report on combined analysis of Cassini VIMS, Synthetic Aperture Radar (SAR), and ISS observations of Arrakis Planitia acquired in the years following the 2005 precipitation event. The low-albedo surface (observed in 2005 ISS images) correlates with local topography (inferred from 2008 SAR data), consistent with a liquid that has pooled on the surface. Like the equatorial event, the low-albedo surface at Arrakis Planitia is observed in VIMS data acquired from 2007 to 2009 to increase in albedo. Unlike the tropics event, however, four years after the initial precipitation event (more than 2 years after the increased albedo was first observed), these south-polar regions were still bright compared to their pre-precipitation albedo. The combined results support the hypothesis that hydrocarbons rained onto Titan’s surface and subsequently froze. Furthermore, because Titan's lakes and seas are almost certainly liquid, our results imply that some mechanism is preventing Titan's lakes and seas from freezing - one obvious hypothesis is that Titan’s lakes and seas differ in composition from Titan’s presumed methane-rich rain (likely the result of the concentration of minor constituents).
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #46
- Pub Date:
- November 2014
- Bibcode:
- 2014DPS....4611207S