Hydrocarbon lakes on Titan and their role in the methane cycle

Abstract

Saturn's moon Titan is the only extraterrestrial body currently known to support standing bodies of liquid on its surface and, along with Earth and Mars, is one of only three places that we know to posses or have possessed an active hydrologic cycle. Understanding the nature of Titan's hydrologic system will teach us about the history of volatile compounds across the solar system and help define Earth's place within it. Titan's hydrologic cycle represents a simpler version of Earth's water cycle, lacking an ocean as a global sink of liquid and heat, and acts as a model for the evolution of planets around other stars, as its methane-based system may be more common than Earth's water-based system. This thesis combines several studies related to Titan's hydrologic system, particularly focusing on the role of lacustrine deposits. Following an introduction that discusses Titan's place in the solar system and the importance of studying its methane cycle, chapter two describes the lakes' geographic distribution and models interaction with a porous regolith. The chapter also discusses the implications of a hemispheric asymmetry in lake distribution, which has been attributed to an asymmetry in the intensity of Titan's seasons. The evolution of the orbital parameters that generate this asymmetry provide a mechanism for transferring not only methane, but also less volatile species such as ethane, from pole to pole over tens of thousands of years. Chapter three discusses lake properties through an examination of Ontario Lacus, the largest lake in Titan's southern pole. The complex dielectric properties of Ontario's near-shore region are derived through a combined analysis of radar altimetry and backscatter. The analysis is performed within multiple regions around Ontario's shore, producing a near-shore bathymetry map. The results of this study are then used to measure seasonal variation in chapter four. Shoreline recession at Ontario Lacus and smaller lakes which disappeared between repeat observations suggest an average meter-per-year loss rate between southern summer solstice and autumnal equinox. These observations demonstrate that Titan's surface plays an active role in its methane cycle and can be used to describe the evolution of its hydrologic system.