Facts about Titan, the Solar System’s Most Unique Moon

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Stepping onto the Titanian Surface

An artist’s rendering of the Huygens landing site, inspired by photos of the surface taken by the lander before it stopped transmitting 90 minutes after touching down.

The first thing that you would notice if you were to walk on the surface of Titan is that it is a very dark world, receiving only one percent of the amount of sunlight that Earth does. This is, in part, due to its far greater distance from the Sun, but it’s also down to the extremely dense atmosphere. It is also frigidly cold, with surface temperatures averaging at around -180°C. When the Huygens probe landed, it wobbled on an unstable surface, sinking several inches into the ground. The surface had the consistency of wet sand or snow. Rocks and pebbles which appear to be made mostly from water ice were scattered across this swampy terrain.

The extremely cold temperatures and surface pressure (about 1.5 times higher than the pressure on Earth at sea level) on Titan allow for methane and ethane to exist in liquid form. This allows Titan to have small lakes and rivers, composed primarily of these chemicals, flowing across the surface just like water does on Earth, only they only cover a few percent of the moon’s surface. In fact, in December 2012, a river remarkably like the Nile was discovered on Titan, flowing with liquid ethane. It meanders into one of Titan’s largest lakes, Ligeia Mare. Adding to the many oddities of this orange moon is also the possibility that it might contain a liquid ocean beneath its soft and crusty surface.

Titan is much smaller and less massive than Earth and, because of this, it has only a fraction of the amount of gravity that Earth has. This is one of the reasons why the atmosphere extends far above the surface. In fact, the entire mass of the atmosphere is about 20% greater than that of Earth. The atmosphere is composed almost entirely of nitrogen with around 1.4% methane and trace amounts of hydrogen and certain other elements.

Storms occur quite regularly over the Titanian surface, particularly in the south pole region where there is a permanent vortex ravaging the land. It also rains a concoction of liquid methane and ethane, albeit only rarely. The Cassini-Huygens mission discovered puddles of the alien liquid on the surface following a storm. Titan even has seasonal weather patterns like Earth although, due to it being a moon, the seasons work in quite a different way to what we’re used to.

The Cassini-Huygens mission also discovered mountains on Titan, indicating that there has been plenty of geological activity in the moon’s more recent history. These mountains are composed of icy materials and are covered by a layer of methane snow. Titan is a geologically young moon, and it has been hypothesised that there may be cryovolcanoes on the surface, which are found on various other moons belonging to Jupiter and Saturn. Instead of throwing molten rock into the atmosphere, they erupt with volatile materials such as methane and ammonia.

After six years of exploration, the orbiting Cassini probe has put together an almost complete map of the Titanian surface, and the results show some geographical features remarkably like those found on Earth. One of the most prominent areas is the Xanadu, a raised region around the equator about the size of Australia. The area is covered in dunes, valleys, rivers and hills. Beside it is the sunken land of Shangri-La, the darkest region of the Titanian surface. These were originally thought to be seas, although recent reports suggest that they are currently dry.

At the time of writing, the Cassini-Huygens mission had just entered its final phase which, after a highly successful run, will eventually end with the orbiting module crashing into the Saturnian clouds early next year.

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