MIT discovers surprising tidal activity on Titan, Saturn’s largest moon

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

myth Researchers have used simulations to suggest that Titan’s shores, SaturnIts largest moon is formed by waves. This discovery is based on images from NASAS ‘ Cassini spacecraft, which first confirmed the existence of Titan’s methane and ethane bodies. Understanding how these waves can erode coastlines could provide insights into Titan’s climate and the future evolution of the sea.

Titan’s unique extraterrestrial “waters”.

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 as large as Earth’s Great Lakes.

The existence of Titan’s large seas and smaller lakes was confirmed in 2007, with images taken by NASA’s Cassini spacecraft. Since then, scientists have pored over those and other images for clues about the moon’s mysterious liquid environment.

Now, MIT geologists have studied Titan’s shores and shown through simulations that the moon’s vast seas were likely formed by waves. So far, scientists have found indirect and conflicting signs of wave activity based on distant images of Titan’s surface.

Waves as an erosive force on Titan

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

The researchers emphasize that their results are not conclusive; to confirm that there are waves on Titan, direct observations of wave activity on the moon’s surface will be required.

“We can say, based on our results, that if the coastlines 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 waves of liquid methane and ethane crashing ashore and crashing onto the shores during storms. And they would be able to erode the material that the shore is made of.”

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

Controversies and insights into Titan’s wave activity

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

“Some people who tried to see evidence of waves saw none and said, ‘These seas are as smooth as mirrors,'” says Palermo. “Others said they saw some roughness on the liquid surface, but were not sure if waves caused it.”

Knowing whether the wave activity of Titan’s seas can give scientists information about the moon’s climate, such as the strength of the winds that can drive such waves. The tide information 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 the Titan images, Perron says the team had to “take a different route and see, just by looking at the shape of the coastline, if we could tell what was eroding.” the coasts.

Simulation techniques and erosion scenarios

Titan’s seas are thought to have formed as rising liquid levels flooded a landscape crisscrossed by river valleys. The researchers based on three scenarios for what could have happened next: no coastal erosion; wave driven erosion; and “uniform erosion,” driven either by “dissolution,” in which fluid passively dissolves the material of a bank, or a mechanism in which the bank gradually wears away under its own weight.

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

“Wave erosion is driven by wave height and angle,” explains Palermo. “We used fetch to approximate wave height, because the greater the fetch, the longer the distance the wind can blow and the waves can grow.”

To test how shoreline shapes would change 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 retreat distance from every single point along the shoreline to every other point and converted these distances to wave heights. Next, they ran their own simulation to see how waves would erode the original shoreline over time. They compared this to how the same coastline would evolve under erosion driven 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. At most, uniform erosion produced swelled banks that widened evenly all around, even in flooded river valleys, while wave erosion largely eroded long-distance exposed portions of coastlines, leaving valleys flooded narrow and rough.

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

The team checked their results by comparing their simulations with actual lakes on Earth. They found the same difference in shape between Earth’s lakes known to have been eroded by waves and lakes affected by uniform erosion, such as the dissolution of limestone.

Mapping and modeling of Titan’s largest seas

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

In particular, they focused on four of Titan’s largest and most 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 the Ontario Lacus, which is about 20 percent the size of its terrestrial namesake.

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

“We’ve found that if shorelines are eroded, their shapes are more stable with wave erosion than with uniform erosion or no erosion at all,” says Perron.

Future Research Directions and Implications

Researchers are working to determine how strong Titan’s winds need to be in order to drive waves that can repeatedly break onto shores. They also hope to decipher, from the shape of Titan’s coasts, which direction the wind mainly blows from.

“Titan presents this case of a completely intact system,” says Palermo. “This can help us learn more fundamental things about how coastlines erode without human influence, and perhaps this can help us better manage our coastlines on Earth in the future.”

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

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