The New Horizons probe achieved a 12,500 Km closest approach to Pluto on 14th July 2015. Processing and analysis of images sent back reveals features that are still a source of astonishment to geologist and planetary scientists. In complete contrast to many predictions that Pluto would be something of a disappointment - just a bland snowball of various ices, Pluto has one of the most contrastive and interesting sets of surface features in the entire Solar System.

In contrast to its moons whose outer layers are mainly water ice, the surface and outer crust of Pluto is composed almost entirely of frozen nitrogen with small amounts of methane, carbon monoxide and water ice. Although the elements other than nitrogen make up only about 2 % of the surface by weight, they play a very important role in the diversity of features observed. The reddish tinge of much of Pluto's surface is due to the presence of tholins - a complex soup of molecules made from the exposure of atmospheric gases to ultra-violet light and cosmic radiation. The methane in the mainly nitrogen atmosphere is crucial to this process.

And similarly the blade formations of Tartarus Dorsa are thought to be composed of a combination of methane and water ice - methane clathrate. The structures are about 500 metres tall and 3 - 5Km apart on average, which makes them some of the steepest formations found on Pluto. Even at the typical temperatures of -230 Deg C occurring on the surface, methane itself is probably too soft to support such structures. Water ice is detected in the Tartarus Dorsa region which suggests the methane clathrate composition of the blades, but it's not known for sure what they are composed of, nor is it known how they formed or even where the basic components of Pluto's surface and atmosphere came from.

Theories of Pluto's surface formation include many spectacular processes, cryo-volcanism, tectonics, liquid nitrogen flows and glacial flows. The lack of craters on Pluto generally suggests that most geological structures are less than 10 millions years old, but the methane clathrate materials that make up the bladed terrain at Tartarus Dorsa could be very ancient, formed billions of years ago and probably of interstellar origin.

The process by which Pluto has acquired and retained as much nitrogen as it has in its crust and atmosphere is also something of a mystery. Although Pluto is losing nitrogen from its atmosphere into space at a much lower rate than was estimated before the New Horizons fly-by, is still thought to be between 50 and 500Kg per second. That rate of loss over the lifetime of the Solar System equates to a layer of solid nitrogen up to 1Km thick over the entire surface of Pluto. Although the Plutonian surface is known to be composed mainly of nitrogen ice, the exact depth of the frozen nitrogen layer is not known exactly - is it measured in metres or kilometres. In any case the most likely source of nitrogen replenishment is from nitrogen sources within Pluto's mantle, but the exact mechanism by which that nitrogen finds its way to the surface is a matter of speculation. Cometary sources are also unlikely as they don't carry much nitrogen and the estimated frequency of impact is much to small to supply the amount if nitrogen Pluto is losing on a continual basis.

The interesting point is that Pluto seems to have a lot of nitrogen - probably more than any other body in the Solar System, that is readily available for off planet exploitation. Nitrogen is probably the scarcest element that is needed in bulk for large scale space colony construction. The only problem with Pluto is that it is rather far away from the rest of the Solar System. Nonetheless the nitrogen there - along with unlimited amounts of water ice available from Charon, could make the vicinity of Pluto an excellent place to practice remote space colonization, in preparation for eventual Kuiper Belt and Oort Cloud exploration. There are useful amounts of carbon in the Plutonian system, but some elements such as silicon and metals would have to be transported there. There could be a certain trade in nitrogen and other elements between Pluto and other space colonies. Locating a colony further out has many advantages - lack of radiation being one, although a source of power would have to be found, fusion power or beamed power most likely. If things go well there, Pluto may have enough nitrogen for colonies supporting billions of people.