Shores of Titan's Alien Lakes Show Signs of Being Carved by Giant Waves

The roar of the surf may be the soundtrack of Saturn's moon Titan.

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 shorelines, carving out the shapes of the vast rivers and lakes idiosyncratic to the exotic, hazy moon.

This discovery gives fascinating insight into Titan, and the way bodies of liquid may behave on other worlds so different to Earth.

"We can say, based on our results, that if the coastlines of Titan's seas have eroded, waves are the most likely culprit," says geologist Taylor Perron of Massachusetts Institute of Technology (MIT).

"If we could stand at the edge of one of Titan's seas, we might see waves of liquid methane and ethane lapping on the shore and crashing on the coasts 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 has remained hidden from view by a thick, hazy atmosphere that was formally identified when Gerard Kuiper detected methane in its spectrum in 1944. Only when the Cassini probe was sent into Saturn's orbit in the early-2000s was the Kronian moon's surface described in any detail. Detail that included vast, shimmering lakes of liquid hydrocarbon.

Since then, scientists have wondered what these bodies of methane and ethane – some of which rival the Great Lakes of North America in size – are like.

Aside from Earth,Titan is the only known Solar System body with giant liquid reservoirs on the surface, and we are so intrigued. Are its seas tempestuous and always in motion, like the oceans of Earth? Or are they calm and still, 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 did see some roughness on the liquid surface but weren't sure if waves caused it."

To find out, Perron, Palermo, and their colleagues conducted detailed modeling, trying to replicate the shapes of the waterways and lakes seen in images of Titan.

First, they looked at Earth, conducting modeling to figure out how different coastal erosion mechanisms shape the shorelines of bodies of water such as lakes and oceans. This gave them a basic framework for using shoreline morphology to discern the different erosion processes that could be at play around a body of liquid.

Then, they applied this framework to Titan, looking at three specific scenarios: one in which there was no coastal erosion; a second in which erosion was driven by waves; and a third in which erosion was a uniform process, whereby coastal material gradually dissolved, or fell away under its own weight.

Of particular importance is a property known as fetch, the distance over which a wind can pass unimpeded over a body of liquid, transferring energy to the liquid surface as it goes. The longer a wind can travel, the more energy is transferred, and the more wild the surface grows.

"Wave erosion is driven by the height and angle of the wave," Palermo says. "We used fetch to approximate wave height because the bigger the fetch, the longer the distance over which wind can blow and waves can grow."

Under their simulations, the three scenarios produced very different shorelines. The ones that most resembled the real Titan are those in which waves crashed or lapped at the shores. And those with uniform erosion ended up resembling lakes on Earth eroded the same way, such as dissolving limestone.

It's not concrete evidence, of course. We won't know if there are waves on Titan until we go there and take a closer look. There's a mission in the works to do just that, named Dragonfly. It's currently scheduled to arrive at Titan in 2034, so we're just going to have to sit tight until then.

"Titan presents this case of a completely untouched system," Palermo says. "It could help us learn more fundamental things about how coasts erode without the influence of people, and maybe that can help us better manage our coastlines on Earth in the future."

The research has been published in Science Advances.