Charon is the largest moon of Pluto. It has a diameter of 1212 km, an average density of 1.7 and a gravity of 0.029 compared to Earth.
Data from New Horizons spacecraft reveal that Charon is covered by a thick crust of water ice, with many signs of tectonic activity. Scientists suggest that Charon once had a subsurface water ocean, but that ocean is now frozen. What is sure, is that Charon has a differentiated structure, with a rocky core and an icy mantle.
It appears that Charon hasn’t an atmosphere in a classic way. In fact, it shares the same atmosphere with Pluto. During polar nights, some gasses condensate on the polar caps, where they are more easily transformed into tholins, forming dark caps like the Mordor Macula.
Colonizing[]
At its small size, Charon will be unable to host an atmosphere. So, terraforming is out of question. Its surface is made of water ice, so any attempt to build something without insulation will result in melting of the ground. Another problem is that the Pluto - Charon system orbits very far from the Sun. The light is dim, enough for someone to see, but not enough for plants to survive (see Plants on new worlds for details).
Charon's surface appears to be made of water ice, with only small deposits of tholins at the poles. This will not attract too many settlers and industrial corporations, unlike its much richer parent, Pluto. Rich in methane, nitrogen, carbon dioxide and tholins, Pluto will become an important source of organic compounds, so much needed for plastic and rubber, once Earth's fossil fuels will be exhausted.
Still, with its subsurface ocean recently frozen, it is possible for Charon to host some rare and high-density deposits of salts.
It is also possible that tholins, mined on Pluto, will be refined on Charon. The low gravity will allow spaceships to ferry between the two very easy. Chemical industry can take the advantage and boost the economy.
If we want to terraform Titan, we might destroy its rich deposits of organics. Pluto, which orbits too far for plant life to develop, will become an important source for the industry.
Goods from Pluto and Charon will be sent to Styx and from there to all parts of the Solar System.
To provide a suitable place for humans to live, some parts of Charon can undergone Paraterraforming, becoming large greenhouses. However, in those areas, we have to provide both heat extra light.
Although not feasible, a global paraterraforming is possible for both Pluto and Charon, as shown in this video.