Methane sea discovered on Saturn’s largest moon

Titan, the largest moon of the gas giant Saturn and the second-largest moon in the Solar System, is a significant celestial body, both for having a dense and opaque atmosphere, which makes Titan unique among other natural satellites in the Sun's family, and for hosting lakes and seas of liquid hydrocarbons. We know that its atmosphere is largely nitrogen-dominated, just like that of the Earth, but the exact make-up of its vast surface reservoirs remained a mystery until recently.

Data received from the NASA/ESA unmanned spacecraft Cassini between 2007 and 2015 revealed that due to Titan’s frigid temperatures, the Ligeia Mare, one of its seas, is mostly filled with pure methane, with a seabed covered by a sludge of organic-rich material, and possibly surrounded by wetlands.

“Before Cassini, we expected to find that Ligeia Mare would be mostly made up of ethane, which is produced in abundance in the atmosphere when sunlight breaks methane molecules apart. Instead, this sea is predominantly made of pure methane,” said Alice Le Gall, a Cassini radar team associate at the French research laboratory LATMOS in Paris.

According to the new study, published in the Journal of Geophysical Research: Planets on Monday, there are several possible explanations to account for the surprising presence of methane, instead of ethane, in the sea.

“Either Ligeia Mare is replenished by fresh methane rainfall, or something is removing ethane from it,” said lead author Alice Le Gall.

“It is possible that the ethane ends up in the undersea crust, or that it somehow flows into the adjacent sea, Kraken Mare, but that will require further investigation,” she added.

The Cassini orbiter has also revealed that more than 1.6 million square kilometers of Titan – almost two percent of the moon’s surface – are covered in liquid.

The space probe was launched in 1997 to study Saturn and its crowded family, and it has been busy with numerous flybys of the planet and its moons, studying them and sending data back to the Earth since its arrival at the gas giant in 2004.

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