Monash University Scientists Demystify The Origin of Titan’s Dunes

Dunes are a common feature in landscapes across the inner Solar system - including on Earth and Mars. But they also exist beyond the asteroid belt, with some of the most mystifying dunes on Titan - one of Saturn’s moons. However, it’s unclear how these vast expanses of dunes developed and where the sediment came from.

Now, a new study led by Monash University researchers is providing clues into how dunes form throughout the Solar system - in particular, on Titan.  

“We have no clear handle on how the dunes that encircle the moon Titan around its equator developed, especially where the sediment they are made out of came from,” said Dr Andrew Gunn, the lead author of the study, from the Monash University School of Earth, Atmosphere and Environment.

“The debates on Titan and Pluto are around how the dunes even got there.”

To understand where the sediment for dunes came from, there are two key pieces of information scientists need - the minimum wind speed needed to move sediment, and how fast sediments break apart. 

Dunes are an aeolian feature, meaning they are formed by winds, hence why knowing the wind speed needed to move sediments is important. If winds don’t meet the minimum wind speed to move sediments, they can’t accumulate and shape into dunes. This helps to determine why dunes form in some areas but not others on planets and moons across the Solar system.

When the wind blows sediments around, individual particles will bounce across the ground, which sends other particles bouncing across the ground. This is called saltation. The crashing of sediment particles into the ground and one another breaks them down over time. Softer sediments will break apart faster than harder ones, so knowing how fast sediments are breaking apart can inform scientists about the likely material they are made of. Once sediment particles get very small, they don’t aggregate into dunes anymore.

“Our work provides the most robust predictions for what wind speeds must be in order to move sediment, placing a lower bound on the maximum winds each body’s atmosphere must achieve to make the dunes present on its surface.”

“We also provide a measure for how fast sediment would break apart when moved in those conditions.”

The researchers compiled data from experiments on Earth as well as observations from space missions that describe the properties of sediments and atmospheres across the Solar system, as well as data from experiments that directly measure the wind speeds required to move sediment. 

Combining both theory and data, the researchers produced predictions for Earth, Mars, Venus, Titan, Pluto, and Triton. These predictions were then interpreted in light of active debates regarding these different planetary bodies.

“We show that sediment (not sand, either ice or organics, or a mix) cannot be from far away from where the dunes presently are since our results indicate that the sediment particles can obliterate each other to dust as they collide when the wind blows them over relatively short distances,” said Dr Gunn.

“Our study is significant because it shows for the first time that we can assess, for any given planetary body we have evidence of dunes on, how dynamic the atmospheres are, what its surface chemical composition is, and how sediments are produced, by just using first-principles physics—these are first-order questions when deciding on a planetary body’s potential for life and need for further study.”