Stratification Dynamics of Titan's Lakes via Methane Evaporation


Modes of Stratification. The temperature of the lake determines the mode of stratification. Above 86K, a liquid methane–ethane–nitrogen mixture on Titan will remain well mixed, preventing stratification. Between 84 and 86K, the mixture becomes polymictic, undergoing cycles of stratification and overturn, until the bulk composition is poorer in methane than the local density minimum and becomes holomictic. Below 84K, the mixture becomes meromictic, eventually forming a nearly methane-free epilimnion.

Saturn's moon Titan is the only extraterrestrial body known to host stable lakes and a hydrological cycle. Titan's lakes predominantly contain liquid methane, ethane, and nitrogen, with methane evaporation driving its hydrological cycle.

Molecular interactions between these three species lead to non-ideal behavior that causes Titan's lakes to behave differently than Earth's lakes. Here, we numerically investigate how methane evaporation and non-ideal interactions affect the physical properties, structure, dynamics, and evolution of shallow lakes on Titan. We find that, under certain temperature regimes, methane-rich mixtures are denser than relatively ethane-rich mixtures. This allows methane evaporation to stratify Titan's lakes into ethane-rich upper layers and methane-rich lower layers, separated by a strong compositional gradient. At temperatures above 86K, lakes remain well-mixed and unstratified.

Between 84 and 86K, lakes can stratify episodically. Below 84K, lakes permanently stratify, and develop very methane-depleted epilimnia. Despite small seasonal and diurnal deviations (<5K) from typical surface temperatures, Titan's rain-filled ephemeral lakes and "phantom lakes" may nevertheless experience significantly larger temperature fluctuations, resulting in polymictic or even meromictic stratification, which may trigger ethane ice precipitation.

Jordan K. Steckloff, Jason M. Soderblom, Kendra K. Farnsworth, Vincent F. Chevrier, Jennifer Hanley, Alejandro Soto, Jessica J. Groven, William M. Grundy, Logan A. Pearce, Stephen C. Tegler, Anna Engle
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2006.10896 [astro-ph.EP] (or arXiv:2006.10896v1 [astro-ph.EP] for this version)
Submission history
From: Jordan Steckloff
[v1] Thu, 18 Jun 2020 23:33:52 UTC (4,603 KB)
https://arxiv.org/abs/2006.10896
Astrobiology, Astrochemistry

Please follow Astrobiology on Twitter.


  • submit to reddit