Saturn's moon Titan has shorelines shaped by waves

Saturn’s largest moon, Titan, is the only other planetary body in our solar system with active rivers, lakes, seas and waves. These rivers are thought to be filled with liquid methane and ethane, flowing into large lakes and seas that rival the Great Lakes on Earth.

According to NASA, the largest of Titan’s seas are hundreds of feet deep and hundreds of miles wide. 

In 2007, NASA’s Cassini spacecraft confirmed the existence of Titan’s large seas and smaller lakes. Since then, scientists have been analyzing these and other images to understand Titan’s mysterious liquid environment.

A recent study by geologists has revealed that waves likely shaped Titan’s large seas, a finding based on simulations rather than direct observations.

Simulating waves on Titan

Geologists from the Massachusetts Institute of Technology explored Titan’s shorelines using simulations. They first modeled how a lake erodes on Earth and then applied these models to Titan’s seas to identify the most likely erosion mechanisms seen in Cassini’s images.

Waves, they concluded, were the most probable cause. Direct observations of wave activity on Titan are still needed to confirm this theory.

“If the coastlines of Titan’s seas have eroded, waves are the most likely culprit,” explained Taylor Perron, a professor of Earth, Atmospheric and Planetary Sciences at MIT.

“Standing at the edge of one of Titan’s seas, we might see waves of liquid methane and ethane lapping on the shore and crashing during storms, capable of eroding the coastal material.”

Understanding wave activity on Titan

The presence of waves on Titan has been debated since Cassini spotted liquid bodies on the surface of the moon. Some scientists saw no evidence of waves, describing the seas as “mirror-smooth,” while others noticed roughness but could not confirm if it was caused by waves.

Understanding wave activity on Titan could provide insights into the moon’s climate, wind strength, and how its seas might evolve over time.

Instead of searching for direct wave evidence in images, the MIT team examined the shape of the shorelines to deduce what might be eroding the coasts. Titan’s seas are believed to have formed as rising liquid levels flooded a landscape crisscrossed by river valleys.

The researchers considered three scenarios: erosion driven by waves, no coastal erosion, and uniform erosion driven by dissolution or gradual sloughing off of the coast under its own weight.

Based on a property known as fetch, which is the distance over which wind can blow and waves can grow, they simulated how shoreline shapes would evolve under each scenario. The simulations showed that wave-driven erosion produced distinctly different shoreline shapes compared to uniform erosion.

“We found that you get a really different final shape under uniform erosion versus wave erosion,” said Perron. “Wave erosion mainly smooths parts of the shorelines exposed to long fetch distances, leaving the flooded valleys narrow and rough.”

Comparing Earth and Titan

The researchers validated their simulations by comparing them to actual lakes on Earth. They observed the same differences in shape between Earth lakes eroded by waves and those affected by uniform erosion.

The team then focused on Titan’s largest, well-mapped seas: Kraken Mare, Ligeia Mare, Punga Mare, and Ontario Lacus.

Mapping Titan’s shorelines using Cassini’s radar images, the researchers found that all four seas fit solidly within the wave-driven erosion model. This suggests that waves likely shaped these seas.

Strength of Titan’s winds

The team is now working to determine how strong Titan’s winds must be in order to generate waves capable of eroding the coasts. By studying the shapes of Titan’s shorelines, the experts also aim to identify the predominant wind directions.

This dual approach helps to understand how wind forces contribute to coastal erosion and the overall landscape dynamics of Titan. The insights could provide valuable information about the moon’s climate and its evolving geological features.

“Titan presents a case of a completely untouched system,” noted Rose Palermo, a former MIT-WHOI Joint Program graduate student and a research geologist at the U.S. Geological Survey.

“It could help us learn more fundamental things about how coasts erode without human influence, and maybe that can help us better manage our coastlines on Earth in the future.”

The study is published in the journal Science Advances.

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