The roar of the surf may be the soundtrack to Saturn’s moon Titan.
A new analysis shows that the vast bodies of liquid methane and ethane that wrap around Titan’s surface are likely populated by waves that erode the banks and carve out the shapes of the vast rivers and lakes that are typical of the exotic, hazy moon.
The discovery provides a fascinating look at Titan and how liquid bodies might behave on other worlds so different from Earth.
“Based on our results, we can say that if the coasts of Titan’s seas have eroded, waves are the most likely culprit,” says geologist Taylor Perron of the Massachusetts Institute of Technology (MIT).
“If we could stand at the edge of one of Titan’s seas, we could see waves of liquid methane and ethane crashing ashore and hitting the coast during storms. And they would be capable of eroding the material that the coast is made of.” .”
Discovered by Christiaan Huygens in 1655, Titan’s surface remained hidden from view by a dense hazy atmosphere, which was formally identified when Gerard Kuiper detected methane in its spectrum in 1944. It wasn’t until the Cassini probe was sent into Saturn’s orbit in the early 2000s. the surface of the Kronian moon was described in detail. A detail that included vast, shimmering lakes of liquid hydrocarbons.
Since then, scientists have wondered what these bodies of methane and ethane—some of which rival North America’s Great Lakes in size—are.
Other than Earth, Titan is the only known body in the Solar System with giant reservoirs of liquid on its surface, and we’re intrigued. Are its seas stormy and constantly in motion like Earth’s oceans? Or are they calm and motionless, without significant movement?
“Some people who tried to see evidence for waves didn’t see any and said, ‘These seas are mirror-smooth,'” says geologist Rose Palermo of the US Geological Survey. “Others said they saw some roughness on the surface of the liquid, but they weren’t sure if it was caused by the waves.”
To find out, Perron, Palermo and their colleagues performed detailed modeling and tried to replicate the shapes of waterways and lakes seen in images of Titan.
First, they looked at Earth and did modeling to see how different mechanisms of coastal erosion shape the shores of bodies of water such as lakes and oceans. This gave them a basic framework for using shoreline morphology to discern the various erosional processes that might be at play around the body of liquid.
They then applied this framework to Titan and looked at three specific scenarios: one in which there was no coastal erosion; the second in which erosion was driven by waves; and a third in which erosion was a uniform process in which coastal material gradually dissolved or sank under its own weight.
Of particular importance is a property known as fetch, the distance that wind can pass undisturbed through a body of liquid and transfer energy to the surface of the liquid. The longer the wind can travel, the more energy is transferred and the wilder the surface grows.
“Wave erosion is controlled by the height and angle of the wave,” says Palermo. “We used fetch to approximate the height of the wave because the higher the fetch, the longer the distance the wind can blow and the waves can grow.”
According to their simulations, the three scenarios produced very different shorelines. The ones that most closely resembled the real Titan are the ones in which the waves crashed or whipped the shores. And those with uniform erosion ended up as lakes on Earth eroded in the same way as limestone is dissolved.
Of course, this is not concrete evidence. We won’t know if there are waves on Titan until we go there and take a closer look. This is what the mission called Dragonfly is ready for. It’s currently scheduled to arrive on Titan in 2034, so we’ll just have to sit tight until then.
“Titan represents this case of a completely pristine system,” says Palermo. “It could help us learn more fundamental things about how coastlines erode without human influence, and maybe help us better manage our coasts on Earth in the future.”
The research was published in Scientific advances.