If there’s alien life on Titan, it’s like nothing we’ve ever seen before. Titan and Earth both have thick atmospheres made mostly out of nitrogen. But that’s about where the similarities end. Saturn’s largest moon barely has any oxygen in its atmosphere, which is probably a good thing, since it would make the moon highly flammable.
Because unlike Earth, which is composed of mostly water on its surface, Titan is thought to be covered in seas of hydrocarbons, such as ethane and methane. New observations from the Cassini spacecraft orbiting Saturn support the idea that one of the moon’s largest lakes, Ligeia Mare, is comprised mostly of liquid methane.
Previously scientists figured ethane would make up the majority of Ligeia Mare. They figured sunlight would break down methane, the second-most common molecule in Titan’s atmosphere, causing two CH3 molecules to bind together into ethane that rains down onto the surface. However, scans taken between 2007 and 2015 suggest methane is the primary component of the lake.
Cassini scientist Alice Le Gall has a few hypotheses.
“Either Ligeia Mare is replenished by fresh methane rainfall, or something is removing ethane from it,” she says. “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.”
The study also suggested that Ligeia Mare’s seabed may be covered by a layer of organic sludge. Le Gall and her team think that after the nitrogen and methane molecules react in Titan’s atmosphere, the heavier, insoluble molecules sink the bottom of the lake.