Times are displayed in (UTC-05:00) Central Time (US & Canada) Change

Mantled Karst as an Analog for Titan’s Sharp-Edged Depression Lakes.

Session: Geomorphology and Surface Processes Across the Solar System

Presenting Author:

Michael James Malaska

Authors:

Malaska, Michael James¹, White, Oliver², Howard, Alan³, Moore, Jeffrey⁴, Umurhan, Orkan⁵

(1) Jet Propulsion Laboratory / California Institute of Technology, Pasadena, CA, USA; Blue Marble Space Institute of Science, Seattle, WA, USA, (2) SETI Institute, Mountain View, CA, USA, (3) PSI, Tucson, AZ, USA, (4) SETI Institute, Mountain View, CA, USA; NASA Ames Research Center, Moffett Field, CA, USA, (5) SETI, Mountain View, CA, USA,

Abstract:

The majority of lakes found on Saturn’s moon Titan are found in sharp edged depressions (SEDs). These depressions are characterized by steep scarps inset in a thick organic substrate. They are often, but not always, filed with hydrocarbon liquids such as cryogenic methane. Titan’s lakes are large: the smallest observed lakes on Titan are several orders of magnitude above the resolution limit. (Fun fact: the smallest lakes on Titan are bigger than the largest natural lake in England.) The lakes have a lognormal size distribution rather than a power law distribution: this suggests a minimum size for Titan lakes. In addition, ss the lakes become larger, their circularity decreases, possibly due to growth from mergers and coalescence of multiple lakes. Nearest neighbor analysis shows that SEDs have a local near uniform distribution across the region where they are found. Many of the lakes show multiple stands as liquid levels fluctuated. The similarity of the surface elevation of many lakes in the same region noted by Birch et al in 2017 suggests a subsurface connection of the liquid level.

We compared several characteristics of Titan’s SED’s with mantled karst lakes found in Florida, particularly in the Hawthorne Lakes region. In analogy with mantled karst on Earth, we find that variations in size and morphology of Titan’s SEDs could be explained by the presence of porous upper substrate, a constricting aquitard, and a deeper aquifer. On Titan, the deeper aquifer may be the result of the increased solubilizing power of a lower hydrosphere of residual ethane- or propane-rich hydrocarbons during episodic climactic dry-down. A major driver for Titan’s large lake sizes compared to Earth could be due to horizontal vs. vertical hydraulic conductivity, gravity, pore space compressibility in the organic substrate, and deeper ethane-based aquifer on Titan with higher solubility. The presence of subsurface aquifer moving soluble organics around could have important implications for Titan’s deep habitability. We will present a comprehensive karstic mechanism for the formation of Titan’s SED lakes.