Titan, Saturn’s moon, has a sea called Ligeia Mare that scientists have long speculated might be filled with a liquid goo of methane. NASA’s Cassini spacecraft has finally confirmed this hypothesis. “It’s a marvelous feat of exploration that we’re doing extraterrestrial oceanography on an alien moon,” said Cassini’s Steve Wall.
Out of hundreds of moons in Earth’s solar system, Titan is the only one with large liquid reservoirs on its surface. In some ways Titan is like a terrestrial planet, with a nitrogen-dominated atmosphere similar to Earth. However, the air on Titan contains very little oxygen, and is made up of mostly methane and trace amounts of other gases, such as ethane. Despite the frigid temperatures found on Saturn due to its distance from the sun, methane and ethane can remain in liquid form.
Scientists had suspected that there might be hydrocarbon lakes and seas on Titan, and now the Cassini spacecraft has confirmed that more than 620,000 square miles of the moon’s surface, which is nearly 2 percent of its total area, are covered in liquid.
Ligeia Mare is the second largest of Titan’s three large seas, all of which are located near the moon’s north pole. It was not until 2014 that Cassini’s radar instrument was able to show the composition of these large lakes, and reveal that Ligeia Mare is methane-rich. It also showed that the sea was at deep as 525 feet.
Before Cassini, scientists expected to find that this large lake would be mostly ethane, but were surprised to find that it was nearly pure methane. They also discovered that the seabed of Ligeia Mare is most likely covered by an organic-rich layer of sludge, produced due to the reaction between nitrogen and methane. Scientists think the heaviest of the materials that come from this reaction fall to the surface, some dissolving in the liquid methane and sinking to the sea floor.
Cassini did not measure any large differences between the temperature of the sea and the shore over the period of 2007 and 2015 in which it was doing flybys of Titan, suggesting that the terrains around the seas and lakes are wet with liquid hydrocarbons.
The findings of the NASA scientists were published in the Journal of Geophysical Research: Planets.
Image Credit: NASA/JPL/Univ. Arizona/Univ. Idaho