Dune formation on Titan, Saturn’s largest moon, requires higher wind speeds than expected and the dunes evolve over timescales that are much longer than previously thought. These findings, presented in two independent studies published in Nature and Nature Geoscience this week, offer new insights into the processes that shape sand dunes, which may provide clues about dune formation on other planets and moons.
The wind-blown dune formations on Titan are thought to be similar to those found on Earth, Mars and Venus. Modelling studies have been performed to determine the conditions that produce dunes on Titan, but it is unclear how accurate these models are. Wind tunnel experiments designed to simulate surface conditions on Titan, reported by Devon Burr and colleagues in Nature, indicate that threshold wind speeds required to move sand for dune formation are around 40 per cent higher than predicted by current models. These results lend support to the idea that only rare strong westerly winds control dune movement, rather than the easterly winds that are thought to be most common on Titan.
A second study by Ryan Ewing and colleagues, detailed in Nature Geoscience, analyses images of Titan’s dunes taken by NASA’s Cassini spacecraft. The results imply that long-term climate cycles associated with variations in Saturn’s orbit control the sand-dune patterns on Titan. The authors estimate that the observed reorientation of some dune crests would have taken around 3,000 Saturn years (around 88,000 Earth years) or longer. This timescale exceeds that of diurnal, seasonal, or tidal wind cycles, which have previously been suggested to be drivers of these patterns, and suggests that Titan’s dunes - like large dune fields on Earth - are shaped by long-term climate cycles.