The landscape of Saturn’s moon Titan, which features lakes, rivers, canyons, dissected plateaus, and sand dunes, can be strikingly like Earth’s. The landforms reveal a world with active liquid transport cycles and sedimentary processes. On Titan, however, these processes are moderated by organic hydrocarbon grains and liquid methane instead of silicate rock and liquid water as on Earth. This poses a problem: sand-sized organic grains are more fragile than their silicate counterparts. And yet, Titan’s equatorial sand dunes have likely been active for tens to hundreds of thousands of years, a timescale on which organic grains would have abraded or worn away into dust.

Mathieu Lapôtre (Stanford University) and coauthors put forward a new model to address this conflict. They hypothesize that growth due to sintering — the process of neighboring organic grains being fused together when they are at rest — could counterbalance the abrasion that grains experience when transported by winds or methane rivers. Comparing their calculations to existing data on Titan’s climate and atmospheric modeling, the authors also demonstrate how this balance could explain the latitudinal zoning of Titan’s geomorphology. The equatorial region is dominated by wind transport, which promotes abrasion over sintering and would produce the fine-grained sand necessary for the dune fields. The winds lull in the mid-latitudes, promoting sintering and the formation of coarse-grained sandstone, consistent with the observed plains. In the polar regions, more frequent rainstorms and river flow would carve plateaus made of this organic sandstone into observed dissected labyrinth terrain.

While well-reasoned, this model remains a hypothesis. When the planned Dragonfly octocopter spacecraft lands on Titan in the mid-2030s, it will help validate the model by measuring the composition, shapes, and sizes of grains within the dunes as well as the wind speeds, frequencies, and precipitation rates that shape them. READ MORE