Formation mechanisms of channels on Titan through dissolution by ammonium sulfate and erosion by liquid ammonia and ethane

Data obtained from the Cassini Visual and Infrared Mapping Spectrometer (VIMS), Imaging Science Subsystem (ISS), and Synthetic Aperture Radar (SAR) instruments have revealed an array of fluvial channels on Titan's surface, often several hundreds of kilometers in length. The paucity of impact craters on Titan's surface suggests a formation by fluvial erosion into the water-ice bedrock. Additionally, at the landing site, the Huygens Probe Descent Imager and Spectral Radiometer (DISR) imaged Earth-like rounded cobbles 0.3–15 cm in diameter composed of water ice, reminiscent of rounded stream clasts on Earth. In this paper we examine different fluvial features on Titan, identified by the Cassini spacecraft, and evaluate the possibilities of channel formation by dissolution of ice by a concentrated solution of ammonium sulfate, and by mechanical erosion by flow of liquid ammonia and liquid ethane. We find that chemical erosion of Titan's channels could be completed in 280 to 1100 years (all units of time in this paper are Terrestrial, not Titanian), much shorter than the period of about 84,000 years that a concentrated (NH₄)₂SO₄-H₂O solution could exist as a liquid on the Titan surface. Mechanical erosion of Titan's channels is generally a much slower process, on the order of 10² to 10⁵ years to completion, and is also slower than mechanical erosion of a model river on Earth, averaging 10³ to 10⁴ years. The erosional sequence of the channels on Titan may have started after the formation of water-ice on the surface by the process of chemical dissolution by (NH₄)₂SO₄-H₂O, overlapping, or followed by, a period of mechanical erosion by liquid NH₃. A final stage on the cooling surface of Titan might have been characterized by liquid C₂H₆ as an agent of mechanical erosion.