waves, mudflats and methane seas

Seas of liquid hydrocarbons on Saturn's moon Titan are a known fact. But not so long ago, astronomers considered there are coastlines of a specific structure. Scientists studied their configuration and suggested that they were formed by waves of methane and ethane. The height of such waves can reach one meter.

On July 24, 2012, the Cassini spacecraft flew past Titan for the 85th time. The flyby was part of a series of maneuvers designed to study both Saturn and its many moons. During its primary mission, the spacecraft collected important data about Titan's surface and atmosphere. Cassini also captured an unexpectedly bright reflection on Lake Kivu Lacus.

The vehicle was equipped with a conventional and infrared mapping spectrometer (VIMS), which was used to obtain images and spectral data in the visible and infrared ranges. VIMS images were interpreted as possible irregularities on the surface of the lake from a mixture of the same hydrocarbons. According to scientists, these irregularities may be signs of shallows, waves or gas bubbles rising from the bottom.

The process of formation of shoals on Titan may be the same as on Earth. But in conditions of low temperature and weak gravity on Titan, it has its own peculiarities. Also, irregularities on the surface of such formations may arise due to emerging gas bubbles that rise from the bottom, or due to the action of currents in the atmosphere, creating small waves and moving sediment

“Our models landscape evolutions show that Titan's coastlines are most similar to lakes on Earth that have been eroded by waves.”— speaks Rose Palermo, geomorphologist from the Coastal and Marine Science Center in St. Petersburg, Florida.

There is no definitive evidence of waves on Titan yet, but scientists joke that in the future, astronauts will need to bring surfboards with them!

The sea is agitated once

Reflections recorded by VIMS for a long time were considered waves, but subsequent studies have failed to confirm this. According to Rose Palermo, in the past, the surfaces of lakes and seas on Titan were very calm and smooth. “Perhaps this is explained by the fact that during the observation period the winds on Saturn’s moon were quite weak, so waves were almost not formed. To confirm the presence of waves, we need higher resolution images.”, she added. But it won’t be possible to get such pictures in the near future. The Dragonfly mission, the next expedition to Titan, will be realized in 2034 at best.

Palermo's team decided to look for indirect evidence of waves on Titan. The researchers suggested that Titan's coastlines could have formed in one of three ways:

the first excluded erosion completely;
the second modeled uniform erosion due to the dissolution of bedrock by hydrocarbons;
the third suggested erosion caused by wave activity.

“We created a random virtual model of the surface with rivers and filled the drainage basin, “flooding” the river valleys around the lake. We then reduced the shoreline to 50 percent of its original size.”explains Palermo.

Wave height

Palermo and her team's modeling showed that wave-driven erosion produces shorelines that closely resemble those actually observed on Titan. The scientists also tested their model using data from Earth.

“We applied the same statistical analysis to lakes on Earth, where erosion processes are well known. Our model was able to predict all this with an accuracy of more than 77.5%.”explains Palermo.

According to Rose Palermo, the mechanisms of wave formation on Titan work similarly to those on Earth, but with noticeable differences. The reason is that the conditions on Saturn's moon and on Earth are very different.

“These differences in gravity and material properties contribute to the fact that waves on Titan are higher and steeper than on Earth for the same wind speed.”adds Palermo.

So would it be possible to surf on such waves? Most likely not, because the digital model shows a possible height of several centimeters. But this, as they say, is inaccurate.

“Our research raises many new questions. In what direction are the waves moving? Knowing this will help us understand atmospheric conditions. How high are the waves? Perhaps in the future we will be able to determine this. There is still much to learn.”says Palermo.

The main limitation to the height and strength of Titan's waves is the size of the seas, which are not particularly large. The largest of them, the Kraken Sea, is comparable in size to the Caspian Sea. There is no ocean on Titan, which means the wind has several tens of kilometers to create waves. For comparison: on Earth, wind can drive waves over distances of 1,500 km or more.