Titan, one of Saturn's 57 moons, is widely considered to be the most promising colonization target in the outer solar system. The largest of Saturn's moons, Titan is even larger than the planet Mercury, and is the only moon in the Solar System to have its own atmosphere. The only moon larger than Titan is Jupiter's moon Ganymede. The Jovian moons are considered difficult targets for colonization because of Jupiter's radiation belts, analogous to Earth's van Allen belts but much larger and more intense. A possible motivation for colonizing the moons of Saturn in the next few centuries would be to exploit the rich deposits of helium-3, an ideal fuel for nuclear fusion, in their atmospheres.
Titan's atmosphere is 98.4% nitrogen, in comparison to 80% nitrogen for the Earth, with the remaining portion made up of methane. Titan's atmosphere has made gaining knowledge about the body difficult, until recently when the Huygens lander, dropped by the Cassini probe, descended through Titan's atmosphere and made detailed observations of the surface. Liquid hydrocarbon lakes were found. The thick nitrogen atmosphere, 1.5 times denser than the Earth's, creates a thick fog, which made it hard for the probe to see very far. Radar mapping of the surface has elucidated Titan's surface features, including islands, a coastline, and geysers. Titan is about 1.5 times larger than the Moon.
Titan has all the basic elements necessary for life - carbon, hydrogen, nitrogen, and oxygen. Its numerous hydrocarbons could serve as an excellent energy source for colonists. Pioneers would not need to worry about cosmic radiation, thanks to the thick atmosphere, or Saturn's radiation belts, which are much milder than Jupiter's. Titan's atmosphere is so thick and gravity low enough that human colonists could strap on wings and fly through the skies with their arm power alone! But the thickness of the atmosphere creates pressure equivalent to that experienced by divers under 5 meters of water, requiring pressure suits.
Another problem is the trace amounts of hydrogen cyanide in Titan's atmosphere, which can kill a human in a few minutes at concentrations as low as 300 ppm. Titan's colonists may benefit from air filters using nanotechnology, perhaps even implanted into their lungs.