Modeling Wind-Driven Waves on Other Planets: Applications to Mars, Titan, and Exoplanets

Abstract

Waves could exist on any planet with sustained winds and stable surface liquids. However, differences in atmospheres, liquids, and gravity confound efforts to extend Earth-based empirical wave models to other planetary environments. We adapted a physics-based numerical wave model to study how planetary conditions affect the growth of waves. We modeled lakes of water on ancient Mars, liquid nitrogen and hydrocarbons on past and present Titan, sulfuric acid on the exo-Venus Kepler 1649-b, liquid water on the super-Earth LHS 1140-b, and liquid rock on the super-Earth 55 Cancri-e. We find that the threshold for wave generation is lower for liquids with weaker surface tension and under higher atmospheric pressure and lower gravity. We also find that waves grow taller in less dense liquids and under higher atmospheric pressure and lower gravity. This suggests that waves on Titan and ancient Mars will begin to grow under weaker winds and grow taller than the equivalent waves on Earth, with a decrease in wave height and an increase in the wave generation threshold as the atmospheric pressure is reduced. Kepler 1649-b and LHS 1140-b both have higher threshold wind speeds and shorter waves. The liquid rock of 55 Cancri-e leads to an even larger wind speed threshold with smaller waves. Our work suggests that the occurrence and size of waves strongly depend on planetary conditions, which affect the timescale and magnitude of shoreline modification, sediment transport, and fluid mixing–ultimately impacting a planet's climate and long-term landscape evolution.