MIT Uncovers Surprising Wave Activity on Titan, Saturn’s Largest Moon

Researchers are finding that wave activity on Saturn’s largest moon may be strong enough to erode the shores of lakes and seas.

HAVE researchers used simulations to suggest that the shores of Titan, Saturnlargest moon, are shaped by waves. This finding is based on images from NASA‘with Cassini spacecraft that first confirmed the existence of methane and ethane bodies on Titan. Understanding how these waves might erode coastlines could offer insight into Titan’s climate and future sea evolution.

The unique alien “waters” of Titan

Titan, Saturn’s largest moon, is the only other planetary body in the Solar System that currently hosts active rivers, lakes, and seas. These otherworldly river systems are thought to be filled with liquid methane and ethane that flow into vast lakes and seas, some of which are as large as Earth’s Great Lakes.

The existence of large seas and smaller lakes on Titan was confirmed in 2007 by images taken by NASA’s Cassini spacecraft. Since then, scientists have been examining these and other images for clues to the moon’s mysterious liquid environment.

Now, geologists at MIT have studied Titan’s coastline and used simulations to show that the moon’s large seas were likely shaped by waves. Until now, scientists have found indirect and conflicting signs of wave activity based on remote images of Titan’s surface.

Waves as erosive forces on Titan

The MIT team took a different approach to investigating the presence of waves on Titan by first modeling the ways in which a lake on Earth might erode. They then applied their modeling to Titan’s seas to determine what form of erosion might have caused the coastline in the Cassini images. They found that waves were the most likely explanation.

The researchers emphasize that their results are not definitive; confirming that there are waves on Titan will require direct observations of wave activity on the Moon’s surface.

“Based on our results, we can say that if the coasts of Titan’s seas have eroded, waves are the most likely culprit,” says Taylor Perron, the Cecil and Ida Green Professor of Earth, Atmospheric, and Planetary Sciences at MIT. “If we could stand at the edge of one of Titan’s seas, we could see the waves of liquid methane and ethane that hit the coast and hit the coast during storms.” And they would be capable of eroding the material that the coast is made of.”

Perron and his colleagues, including first author Rose Palermo, a former MIT-WHOI graduate student and research geologist at the US Geological Survey, will publish their study in an upcoming issue Scientific advances. Their co-authors include MIT research scientist Jason Soderblom, former MIT postdoc Sam Birch, now an assistant professor at Brown University, Andrew Ashton of the Woods Hole Oceanographic Institution, and Alexander Hayes of Cornell University.

Controversy and insights into Titan’s Wave activity

The presence of waves on Titan has been a somewhat controversial topic since Cassini spotted bodies of liquid on the moon’s surface.

“Some people who tried to see evidence of waves didn’t see any and said, ‘These seas are mirror-smooth,'” says Palermo. “Others said they saw some roughness on the surface of the liquid, but they weren’t sure if it was caused by the waves.”

Knowing whether Titan’s seas host wave activity can provide scientists with information about the moon’s climate, such as the strength of the winds that could develop such waves. Information about the waves could also help scientists predict how the shape of Titan’s seas might evolve over time.

Instead of looking for direct signs of wave-like features in images of Titan, Perron says the team had to “take a different tack and see if we could tell what’s eroding the coastline just by looking at the shape of the coastline. .”

Simulation techniques and erosion scenarios

Titan’s seas are thought to have formed when rising liquid levels flooded a landscape criss-crossed by river valleys. The researchers looked at three scenarios of what might have happened next: no coastal erosion; wave-driven erosion; and “uniform erosion”, controlled either by “dissolution” in which the liquid passively dissolves the shoreline material, or by a mechanism in which the shoreline gradually peels away under its own weight.

The researchers simulated how different shoreline shapes would develop under each of the three scenarios. To simulate wave-driven erosion, they took into account a variable known as ‘fetch’, which describes the physical distance from one point on the coast to the opposite side of a lake or sea.

“Wave erosion is controlled by the height and angle of the wave,” explains 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.”

To test how coastline shapes would differ between the three scenarios, the researchers started with a simulated sea with flooded river valleys around its edges. For wave-driven erosion, they calculated the drag distance from every single point along the shoreline to every other point and converted those distances to wave heights. They then ran their simulation to see how the waves eroded the initial shore over time. They compared this to how the same coastline would develop under erosion controlled by uniform erosion. The team repeated this comparative modeling for hundreds of different initial shoreline shapes.

Comparison of types of erosion and their effects

They found that the final shapes were very different depending on the underlying mechanism. Most notably, uniform erosion created inflated banks that spread evenly all around, even in flooded river valleys, while wave erosion mainly smoothed out the long exposed portions of the banks, leaving the flooded valleys narrow and rugged.

“We had the same initial banks and we saw that with uniform erosion versus wave erosion, you get a really different final shape,” says Perron. “They all look like a flying spaghetti monster because of the flooded river valleys, but the two types of erosion create very different endpoints.”

The team verified their results by comparing their simulations with real lakes on Earth. They found the same difference in shape between terrestrial lakes known to have been eroded by waves and lakes affected by uniform erosion such as limestone dissolution.

Mapping and modeling Titan’s largest seas

Their modeling revealed clear, distinctive shoreline shapes depending on the mechanism by which they evolved. The team then wondered: Where would Titan’s coastlines fit within these characteristic shapes?

Specifically, they focused on Titan’s four largest and best-charted seas: the Kraken Mare, which is comparable in size to the Caspian Sea; Ligeia Mare, which is larger than Lake Superior; Punga Mare, which is longer than Lake Victoria; and Ontario Lacus, which is about 20 percent the size of its terrestrial namesake.

The team mapped the shorelines of each Titanian sea using Cassini radar images and then applied their modeling to each of the seashores to determine which erosion mechanism best explained their shape. They found that all four seas fit tightly into a model of wave-driven erosion, meaning that waves created shorelines that most closely resembled Titan’s four seas.

“We found that if shorelines have eroded, their shapes are more consistent with wave erosion than with uniform or no erosion,” says Perron.

Future research directions and implications

Scientists are working to determine how strong the winds on Titan must be to whip up waves that could repeatedly bounce off the coast. They also hope to decipher from the shape of Titan’s shores which direction the wind mainly blows from.

“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.”

Reference: “Signatures of wave erosion in Titan’s coasts” by Rose V. Palermo, Andrew D. Ashton, Jason M. Soderblom, Samuel PD Birch, Alexander G. Hayes, and J. Taylor Perron, 19 Jun 2024, Scientific advances.
DOI: 10.1126/sciadv.adn4192

This work was supported in part by NASA, the National Science Foundation, the USGS, and the Heising-Simons Foundation.