Titan, Saturn’s largest moon, is the only known planet other than Earth that still retains liquid water. Liquid hydrocarbons fed by rain from Titan’s thick atmosphere form rivers, lakes, and oceans, most of which are found in the polar regions. In a new study, a team of MIT geologists surveyed Titan’s coastline and found that the moon’s large lakes and oceans were likely formed by waves.
Artist’s rendering of the surface of Saturn’s largest moon, Titan. Image by Benjamin de Bivort, debivort.org / CC BY-SA 3.0.
The existence of waves on Titan has been a somewhat controversial topic ever since NASA’s Cassini spacecraft discovered liquid puddles on Titan’s surface.
“Some people who have looked for evidence of waves haven’t seen any waves at all and have said, ‘The ocean is as smooth as a mirror,'” said Dr. Rose Palermo, a geologist with the U.S. Geological Survey. “Others have said they saw some roughness in the water but didn’t know if it was caused by waves.”
“Knowing whether there is wave activity in Titan’s oceans can provide scientists with information about the moon’s climate, including the strength of the winds that generate such waves.”
“Wave information could also help scientists predict how the shape of Titan’s ocean will change over time.”
“Rather than looking for direct signs of wave-like features in Titan images, we wanted to take a different approach and see if just looking at the shape of the coastline could tell us what it is that is eroding the coast.”
Titan’s oceans are thought to have formed when rising waters flooded a landscape crisscrossed by river valleys.
The researchers zeroed in on three scenarios for what happened next: no coastal erosion, wave-driven erosion, and uniform erosion caused by either dissolution, where liquids passively dissolve coastal material, or a mechanism where the coast gradually peels away under its own weight.
They simulated how different coastline shapes would change under each of the three scenarios.
To simulate wave erosion, the researchers took into account a variable called “fetch,” which describes the physical distance from one point on the shoreline to the other side of a lake or ocean.
“Wave erosion depends on the height and angle of the waves,” Dr Palermo said.
“We used the fetch to estimate wave height because the bigger the fetch, the further away the wind will blow and the bigger the waves will be.”
Cassini observed Titan’s surface with microwaves and found several grooves that are deep canyons filled with liquid hydrocarbons, including Vid Fulmina, a branching network of thin lines in the upper left quadrant of the image. Image credit: NASA / JPL-Caltech / ASI.
To test how coastline shape would differ between the three scenarios, the scientists started with a simulated ocean area with a flooded river valley all around it.
For wave erosion, we calculated the fetch distance from every point along the coastline to every other point and converted that distance to wave height.
They then ran simulations to see how waves would erode the original shoreline over time.
They compared this to how the same coastline would change due to erosion caused by uniform erosion.
The authors repeated this comparative modelling for hundreds of different initial shoreline configurations.
They found that the shape of the termini varies greatly depending on the underlying mechanism.
Most notably, uniform erosion produced a bulging shoreline that was evenly distributed all around, even in flooded river valleys, whereas wave erosion smoothed out portions of the shoreline exposed primarily to long downstream distances, leaving the flooded valleys narrow and rough.
“Although the initial coastline was the same, we found that uniform erosion and wave erosion resulted in very different final shapes,” Dr Perron said.
“Although it looks like a flying spaghetti monster because of the flooded river valley, the endpoints created by the two types of erosion are very different.”
This image is a composite of images taken during two flybys of Titan in 2006. A large circular feature near the center of Titan’s disk may be the remnant of a very old impact basin. The mountain range southeast of the circular feature and the long, dark linear feature northwest of the old impact site may be the result of deformation of Titan’s crust caused by energy released when the impact occurred. Image credit: NASA/JPL/University of Arizona.
Dr. Perron and his colleagues verified their results by comparing their simulation results with actual lakes on Earth.
They found the same shape differences between Earth’s lakes known to have been eroded by waves and those affected by homogeneous erosion, such as dissolved limestone.
Their modelling revealed distinct and distinctive shapes depending on the mechanism by which the shoreline evolved.
So they wondered: Where does Titan’s coastline fit into these distinctive shapes?
In particular, they focused on four of Titan’s largest and best-mapped oceans: 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 Lake Ontario, which is about 20% the size of the land-based lake of the same name.
The researchers used Cassini’s radar images to map the coastlines of each of Titan’s oceans, and then applied their model to the coastlines of each ocean to see which erosion mechanisms best explain their shape.
They found that all four oceans fit closely to the wave-induced erosion model, meaning that waves created the closest coastlines to Titan’s four oceans.
“We found that when the shoreline is eroding, its shape is more consistent with wave-driven erosion than uniform erosion or no erosion,” Dr Perron said.
Scientists are trying to figure out how strong Titan’s winds would need to be to churn up waves strong enough to repeatedly scrape away the shoreline.
They also hope to learn from the shape of Titan’s coastline which direction the winds primarily blow from.
“Titan shows us that this case is completely pristine,” Dr. Palermo said.
“It may help us learn more fundamental things about how coasts erode without human influence, which in turn may help us better manage coastlines around the world in the future.”
of Investigation result Published in today’s journal Scientific advances.
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Rose V. Palermo others2024. Evidence of wave erosion on Titan’s coast. Scientific advances 10(25); Source: 10.1126/sciadv.adn4192
Source: www.sci.news
