Post contributed by Dr. E. V. Bohacek, European Space Agency (ESA)

In contrast to Earth, where water is cycled through rivers, oceans and the atmosphere, Saturn’s largest moon Titan is a methane world. Liquid methane falls as rain on Titan’s surface, which forms fluvial landforms (rivers), lakes and seas. It is believed that these methane rivers experience episodic activity, with rainfall primarily occurring at the poles and persisting for 10-100 hours per Titan year, equivalent to 30 Earth years (Lorenz, 2014). Another big difference between the fluvial landforms of Titan and the rivers of Earth is their drainage patterns: the distinctive arrangement and organisation of rivers and streams within a river basin. Most rivers on Earth have a dendritic drainage pattern, resembling a branching tree (Image 1 – Yemeni River), whereas on Titan the majority of fluvial landforms branch at right angles in rectangular drainage patterns [Burr et al., 2013] (Image 1 – Titan River). Titan is also covered by vast regions of linear dune fields (Image 1 – Titan Dunes), similar to those observed in the Namib Desert on Earth (Image 1 – Namib Dunes), primarily within the equatorial latitudes [Rodriguez et al., 2014], thought to be composed of hydrocarbon and nitrile sand-sized particles formed from photochemical reactions in Titan’s atmosphere (Hirai et al., 2023). Although observations of Titan are limited to those taken by Cassini-Huygens from 2005-2017, interactions between rivers and dunes have been observed. It is possible that these interactions could partially explain the presence of rectangular drainage patterns. 

Image 1: (Top Left) An example of a typical river valley system on Earth with a dendritic drainage pattern in Yemen [Source: Landsat]. (Top Right) Fluvial landform annotated in blue by Burr et al., (2013) in radar imagery of Titan, showing a rectangular drainage pattern [Source: NASA Cassini]. (Bottom Left) Radar image of linear dunes in the Namib Desert on Earth. The linear dunes, similar in size to those on Titan, are 1-2 km apart. (Bottom Right) Linear dunes in Titan’s sand sea imaged by Synthetic Aperture Radar [Source: NASA Cassini].