Morphological Evidence that Titan’s Southern Hemisphere Basins are Paleoseas

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 (>50o) 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.

SB_Image1

Image 1: Polar stereographic projection of SAR image data of the South polar region extending out to 60o 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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The Geomorphology of Potential Mars Tsunami Deposits

Post by Dr. Alexis Rodriguez. Planetary Scientist, Planetary Science Institute, Tucson, AZ, USA.

The Martian northern lowlands are thought to currently be extensively covered by an ice-rich deposit, interpreted by some researchers to be the residue of an ancient ocean that existed ~3.4 Ga (Kreslavsky and Head., 2002). However, evidence for this ocean has remained a subject of intense dispute and scientific scrutiny since it was first proposed (Parker et al., 1989, 1993) several decades. The controversy has largely stemmed in the fact that the proposed Martian paleo-shoreline features exhibit significant elevation ranges (Head et al., 1999), a lack of wave-cut paleoshoreline features (Malin and Edgett, 1999), and the presence of lobate margins (Tanaka et al., 1997, 2005).

image_1

Fig. 1. Left: Color-coded digital elevation model of the study area showing the two proposed shoreline levels of an early Mars ocean that existed approximately 3.4 billion years ago. Right: Areas covered by the documented tsunami events extending from these shorelines. Lead author Alexis Rodriguez created this figure.

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