Study of Titan sea reveals unexpected composition
We've known for more than a decade thatthe largest of Saturn's moons plays hosts to lakes and seas of liquidhydrocarbons, but the exact make-up of these reservoirs has remaineda mystery. Until now that is, with scientists from the European SpaceAgency (ESA) using data from eight years worth Cassini flybys toconfirm that Ligeia Mare – one of the largest seas on the moon –is made up largely of liquid methane.
In some ways, Titan isn't all thatdifferent from Earth, with a thick atmosphere and expansivereservoirs of liquid on its surface. However, while both our ownplanet and the distant moon have nitrogen-heavy atmospheres, Titan'scontains little oxygen, instead exhibiting high levels of methane.It's also much more distant from the Sun than Earth, allowing methaneto – in theory at least – exist as a liquid on the body'ssurface.
Since arriving at Saturn in 2004, theCassini-Huygens mission has revealed that more than 1.6 million sq km ofTitan (618,000 sq miles) is covered in liquid – equal to roughlytwo percent of the moon's surface. Now, a new study, making use ofCassini data collected between 2007 and 2015, has confirmed the makeup of one of the discovered liquid bodies, known as Ligeia Mare.
Several thermal emissions observationswere used, alongside microwave wavelength readings and data from aradio sounding experiment conducted in 2013. The latter readingsrevealed details of the depth of the sea, finding that it extendsdown 160 m (525 ft) at its most extreme point.
When looking at the data, the teamexpected to find that the sea was mostly made up of ethane, which isproduced when sunlight breaks up methane molecules, but the readingsinstead revealed that the body is mostly pure methane. While thereason for the unexpected composition isn't yet known, scientistshave suggested two possibilities – either some unknown process isremoving ethane from the sea, or fresh methane rainfall is constantlyreplenishing it.
"This study has pinned down, for thefirst time, the basic properties of one of Titan's seas, improvingour understanding of climate and circulation processes on thisfascinating world," said ESA's Cassini-Huygens project scientistNicolas Altobelli.
Full details of the new study arepublished in the Journal of Geophysical Research: Planets.