Post by Samuel Birch, Cornell University, Ithaca, USA.

Titan is the only body in the solar system, besides the Earth, known to currently have standing bodies of liquids on its surface [Stofan et al., 2007]. Presently, liquids are restricted to the polar regions (>50^o) with liquid bodies in the North encompassing 35 times more area as compared to the South [Hayes et al., 2011; Birch et al., 2017a]. Apsidal precession of Titan’s obliquity over ~100,000 year cycles, analogous to the Earth’s Croll-Milankovitch cycles, likely forces liquids from pole-to-pole, and has been invoked as a physically plausible mechanism to account for the dichotomy [Aharonson et al., 2009]. General circulation models support such a mechanism, as Titan’s current orbital configuration produces more intense, high-latitude, baroclinic eddies over the southern hemisphere, preferentially depositing more liquid at the northern pole [Lora & Mitchell, 2015]. These models, therefore, imply that the presence of northern liquids is transient over geologic timescales. Large basins able to accommodate ~70,000 km³ of liquid methane and ethane [Hayes, 2016] are required when orbital and climatic conditions become favorable for the accumulation of southern seas. Our study [Birch et al. 2017b] identifies four large basins, all of which show morphological evidence for having been formerly filled by liquids.

Image 1: Polar stereographic projection of SAR image data of the South polar region extending out to 60^o latitude. SAR image data includes all flybys up to and including T98. A mosaic of ISS data underlays the SAR mosaic. The perimeters of the four basins that we identified are highlighted in yellow.

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