Thermodynamics of Geysers: Application to Titan

General constraints on geyser phenomena are developed and applied to speculative methane geysers on Titan. Variation of boiling point with depth of ethane–methane–nitrogen fluids is found to be of order 0.3 K m−1, in contrast with around 2 K m−1 for water on Earth. It is found that geysers are possible on Titan but require enhancements of ∼100 above global-average geothermal heat flux, a factor similar to that required on Earth. Eruption velocities of order 25 m s−1 appear to be typical for 10-m-deep geyser vents on both Earth and Titan. While eruption velocities on Earth are usually limited by the low sound speed in water–steam mixtures, sound speeds in Titan fluids are higher and the Titan limit is imposed by the available energy in the boiling fluid. Eruption intervals should be nearly the same for geysers with equivalent plumbing. There is an interesting symmetry between geysers on Titan and those on Earth: The volatility of the relevant fluid scales with the available heat flow.