Titan, the largest moon of Saturn and one of the most fascinating places in the solar system, is a world of rain, rivers, lakes and seas. Unlike Earth though, this alien hydrological cycle is composed of liquid methane rather than water, since the temperatures on Titan are far colder than even at the poles of our own planet.
It had long been theorized, however, that liquid water could actually exist on Titan – underground. Gravitational tugging from Saturn could create enough heat inside Titan to maintain a layer of water, similar to that on another Saturn moon, Enceladus and one of Jupiter’s moons, Europa (and possibly others as well). Literally, an underground ocean.
Now, new evidence from the Cassini orbiter has indicated that there most likely is indeed a Titanian ocean.
Scientists analyzed data from the last six flybys of the moon by Cassini, from February 27, 2006 to February 18, 2011. By looking at variations in the gravitational tugging on Titan by Saturn, they were able to determine the internal structure of the moon much more accurately than before.
The new analysis showed interior “tides” up to about 10 metres (30 feet) tall, which suggest a liquid layer that is pulled and tugged by Saturn’s gravity.
According to Luciano Iess, lead author of the paper and a Cassini team member at the Sapienza University in Rome, Italy: “Cassini’s detection of large tides on Titan leads to the almost inescapable conclusion that there is a hidden ocean at depth. The search for water is an important goal in solar system exploration, and now we’ve spotted another place where it is abundant.”
Titan’s surface is composed mostly of water ice, which leads scientists to think that the ocean below is most likely water. The ocean is most likely a layer between the outer icy crust and the interior solid mantle.
So if there is an ocean, does that mean that life is also possible? Perhaps, but there are still a lot of unknowns, like whether the bottom of the ocean is in contact with rock, like Earth’s, or ice or some other solid material. It is commonly thought that liquid water needs to be in contact with rock in order to form the minerals needed for life to exist.
The ocean may also help to solve another mystery of Titan – the source of its methane. Titan’s atmosphere is composed primarily of methane, but the methane is unstable and will generally be destroyed relatively quickly (in geological time periods). It must be continually replenished, but where is it coming from? A subsurface ocean would be ideal; if, as thought, methane is frozen in Titan’s interior mantle, then the water above, with ammonia mixed in as theorized, could bubble up through the crust, releasing the methane to the surface.
With methane rain, rivers, lakes and seas above and a (probable) water ocean below, Titan is a bizarre and complex world. What other surprises are waiting to be discovered?