The fate of ethane in Titan's hydrocarbon lakes and seas

TL;DR

This study investigates why Titan's lakes are methane-dominated despite ethane being a major expected product, proposing that clathrate interactions trap ethane and favor methane accumulation.

Contribution

It introduces a model of ethane sequestration via clathrate interactions explaining the methane dominance in Titan's lakes.

Findings

Clathrate interactions can trap ethane, leading to methane-dominated lakes.

Ligeia Mare's ethane deficiency may result from clathrate entrapment.

Multiple methane-rich lakes could be common on Titan.

Abstract

Ethane is expected to be the dominant photochemical product on Titan's surface and, in the absence of a process that sequesters it from exposed surface reservoirs, a major constituent of its lakes and seas. Absorption of Cassini's 2.2 cm radar by Ligeia Mare however suggests that this north polar sea is dominated by methane. In order to explain this apparent ethane deficiency, we explore the possibility that Ligeia Mare is the visible part of an alkanofer that interacted with an underlying clathrate layer and investigate the influence of this interaction on an assumed initial ethane-methane mixture in the liquid phase. We find that progressive liquid entrapment in clathrate allows the surface liquid reservoir to become methane-dominated for any initial ethane mole fraction below 0.75. If interactions between alkanofers and clathrates are common on Titan, this should lead to the emergence of many methane-dominated seas or lakes.