Waves on Titan?

Saturn’s largest moon, Titan has active rivers, lakes and seas of liquid ethane and ethane. Some lakes and seas bought to be as large as the Great Lakes on earth. These were confirmed in 2007 with the images captured my NASA’s Cassini spacecraft.

However, MIT geologists are studying the shores of the Saturnian moon and through simulations, shown that the large seas have most likely been formed and shaped by waves. Until recently, scientists have found both indirect and conflicting evidence of wave activity through the images of the lunar surface, making the presence of waves a highly controversial issue. Research geologist Rose Palermo at the U.S Geological Survey said on the topic, "Some people who tried to see evidence for waves didn't see any, and said, "These seas are mirror-smooth," Palermo says. "Others said they did see some roughness on the liquid surface but weren't sure if waves caused it."

The team decided to focus on 4 of Titan’s largest, well-mapped seas; 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 geologists took a different approach in their investigations, by taking inspiration from how rivers on Earth can erode and then applying these models to Titan’s seas in order for them to determine what kind of erosion is happening on the shorelines of the lunar body. The scientists said that they believe the seas on Titan were formed as rising levels of liquid flooded the crisscrossing river valley surface. By looking at this they came up with 3 possible explanations as to why Titan’s shores have eroded like they did. here are Costal erosion (via waves), uniform erosion (driven by either dissolution - when the liquid passively dissolves a coast’s material or some other mechanism in which the coast gradually sloughs of under its own weight.)

To simulate wave driven erosion would affect different shorelines, the researchers used a variable named ‘fetch’ which is the physical distance from one point of a shoreline to the opposite side of a lake or sea. Professor Taylor Perron explains that, "Wave erosion is driven by the height and angle of the wave. 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.” The researchers used this model with a simulated sea with flooded river valleys around its borders, calculated the fetch distance from every point along the shoreline and converted these distances into wave heights. After, they ran the simulation they ran it agin once more to see how waves would erode the starting shoreline over time then compared these sims to a shoreline driven by uniform erosion. This comparative method was repeated 100s of times and the scientists found that the end shapes were very different depending on the underlying mechanism. The simulations showed that uniform erosion would produce evenly widened, inflated shorelines whilst wave erosion would smooth the parts of the shoreline tat would have long fetch distances meaning that the flooded valleys would be narrow and rough. The researchers also compared these results to lakes on earth and fond the same difference between those that had been affected by wave erosion and those that had experienced uniform erosion such as dissolving limestone.

And although the researchers emphasize that the results are not definitive, the most likely explanation for the appearance is from waves, this is through applying the model to previous images of the surface taken by Cassini and finding that all four of the seas in question (Kraken Mare, Ligeia Mare, Punga Mare, and Ontario Lacus) fit almost perfectly in the wave driven model. "We found that if the coastlines have eroded, their shapes are more consistent with erosion by waves than by uniform erosion or no erosion at all," Taylor Perron, the Cecil and Ida Green Professor of Earth, Atmospheric and Planetary Sciences at MIT says. Despite the overwhelming evidence for this, it would have to be confirmed through direct observations of wave activity on the surface of Titan.

Perron commented that, “We can say, based on our results, that if the coastlines of Titan's seas have eroded, waves are the most likely culprit," and that "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."

The researchers are now going to be working to determine how strong the winds on Titan must be to stir up waves capable of altering the landscape and which way this wind must be blowing from the shape of the shores.

So why is it important to know if there is wave on Titan’s surface?

Knowing about wave activity on Titn can help scientists better understand the lunar climate and predict the strength of winds or how the seas will eveolve over time. Understanding wind strength will be crucial for possible future missions to Titan that involve atmospheric entry such as any landers and knowing about the evolution of the seas could pose questions about if there was to be life, albeit in the highly unlikely possibility, how it could adapt and how it has previously evolved to survive in the changing climate. Palermo notes that, “Titan presents this case of a completely untouched system, 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."