Rain on Titan and its influence on splash erosion

Abstract

The Saturnian moon Titan has a methane-based hydrological cycle similar to the water cycle on earth. This includes lakes, fluvial drainage networks, clouds and has evidence for precipitation of methane rain. Here we explore the impact of rainfall on Titan based on an analogue laboratory approach. While the composition and structure of the Titan atmosphere and its cloud systems has been studied by the Cassini-Huygens missions, the chemical composition of rain drops remains undetermined. Recent studies have put forward the possibility of soluble nitrogen within rain drops that were earlier assumed to be purely made of methane. Based on simulations, we find a 77% - 23% distribution of methane and nitrogen. The ratio was used to develop a suitable laboratory analogue approach to study splash erosion by rain drop impacts. Using this analogue approach that involved impacting individual drops on soil sample analogues and custom-built numerical models, we find that that rain drops on Titan can redistribute soil particles at larger distances (30 - 600 mm) than Earth due to different energy transmission percentages from drop to splashed matter (15% - 50% of the drop, in comparison to water). Assuming a particle launch angle of 45◦, soil particles can reach heights of ∼10-70 mm, meaning soil splashing can create visible phenomena and proof for recent rainfall events. Such observables of Titanic rainfall can be used for more detailed surface studies by future missions, such as NASA’s Dragonfly drone.