Intermittent saltation drives Mars-like aeolian activity on Titan

Titan, the largest moon of Saturn, is characterized by gigantic linear dunes and an active dust cycle. Much like on Earth, these and other aeolian processes are caused by the wind-driven mobilization of surface grains, known as saltation. To date, very little is known about the conditions that allow for the occurrence of saltation on Titan. In fact, Titan saltation may be fundamentally different from Earth saltation given the denser atmosphere, the lower gravity, and the cohesion of its surface grains. Here, we draw on experiments, theory, and modeling to progress towards a comprehensive understanding of saltation on Titan. We find that aerodynamic lifting of surface grains requires strong wind speeds due to the high cohesion of the grains. However, saltation may be sustained through granular splash at wind speeds much smaller than those required to initiate grain motion. This suggests that most saltation transport on Titan is intermittent rather than continuous. We account for these insights by proposing a saltation mass flux parameterization specific for Titan conditions that accounts for transport intermittency, and use it to quantify yearly sediment transport with a general circulation model. The results show that Titan’s prevailing atmospheric circulation is capable of generating highly intermittent yet significant saltation, yielding yearly transport rates similar to those on the most active dunes of Mars. Furthermore, we find that accounting for surface topography might be critical to answering open questions related to Titan’s landscape evolution, including the formation of linear dunes in opposite direction to the prevailing circulation. Significance statement The Cassini-Huygens mission has revealed that Titan’s landscape evolution and dust cycle may be controlled by the wind-driven transport of surface grains, known as saltation. It is still unclear, however, how saltation can occur on Titan despite the weak winds and the stickiness of the surface grains. Using a combination of experiments, theory, and modeling, we find that, like saltation on Mars, saltation on Titan can be sustained at much lower wind speeds than those required to lift grains from the surface. Accordingly, the prevailing weak winds on Titan may be capable of driving intermittent yet significant saltation, with transport rates comparable to those observed on the most active dunes on Mars.