The Seas of Titan

As many of you have spotted this week’s guess the planet doesn’t actually come from a planet. This image is from Titan, the largest of Saturn’s moons. We’ll be seeing a few moons and dwarf planets in this series, and maybe the odd asteroid and comet. 

This is quite a famous image, so it’s good that I had a few responses from people who knew it straight away. It shows Ligeia Mare, the second largest of Titans seas. Here is an image of the northern hemisphere of Titan to put these seas into context. The North Pole of Titan is at the centre of the image, which extends out to 50 degrees north. The credit for this image goes to the Cassini Team, NASA/JPL-Caltech/ASI/USGS More information on this area can be found on the Cassini website. The image from Monday's post can be found here.

The result is a detailed map of this strange moon, showing that the northern hemisphere is covered by numerous lakes and seas. This is actually a false colour image, because Titan is shrouded in thick layers of cloud, so it isn’t possible to photograph the surface from orbit as we can with Mars, the Moon, and when the weather permits, Earth. Instead this image was produced using radar. Different materials respond to the radar in different ways, allowing the Cassini team to determine which areas are solid, which are liquid, map the topography of the landscape, and even determine the roughness of the surface. 

Ligeia Mare itself is 420 by 350 km across, so covers a sizable area. It is surrounded by many smaller lakes and may be connected to the other large seas that occupy this part of the Titan’s surface. We are still not certain why this region of Titan has these large bodies of liquid, when other regions do not. 

While it might look like a terrestrial sea, Ligeia Mare wouldn’t be much fun to swim in, since it is composed of liquid hydrocarbons rather than water. It is so cold on Titan that water never thaws and is only found as solid ice. The liquid that makes up these lakes is composed of Methane and Ethane. On Earth we know these chemicals as gasses, but at low temperatures in the outer solar system they exist only in their liquid state. 

Titan is the only body besides Earth to have stable liquid oceans on its surface which makes it a fascinating opportunity to compare how “hydrology” and coastal processes have evolved separately using different materials in two very different temperature regimes.