Neptune is the eight planet in the Sol System and the only one to be atmo-terraformed.
Neptune is the outer of Sol's two ice giants. Like its companion Uranus, Neptune is a gaseous world composed primarily of volatile materials heavier than hydrogen and helium, such as methane, water, and ammonia, which are known in planetary science as 'ices'. It has no solid surface, instead having a steadily thickening atmosphere composed of hydrogen, helium and methane which gives way to a thick, liquid, ice-rich mantle as depth increases, ending eventually in a solid rocky core. The planet has some of the fastest winds in the Solar system, with top speeds of almost 600 m/s (over 2100 km/h) occurring in its dynamic and impressive storm systems.
Because of its long orbital period, the planet's seasons last for 40 years. When one pole of the planet is exposed to sunlight it warms up enough to allow methane to sublimate and leak into space. The Neptunian magnetic field is dramatically offset from the planet's center of mass and not aligned with its rotational axis.
Neptune has a system of fourteen moons, the largest of which by far is Triton. Neptune also has a system of rings, though they are the smallest of any major planet, and rich in dust like the rings of Jupiter. The rings are extremely dark, reflecting less than 2% of the radiation that strikes them. The large outer ring is not smooth and continuous, but rather has several short clumps of material known as 'arcs' along one section. In about 3.6 billion years, Triton's orbit will have decayed inside the Roche limit and the moon will be torn apart into a colossal ring system perhaps more spectacular than Saturn's.
Like most of the gas giants in the Sol System, Neptune formed near the beginning of the creation of the system with a rocky body being surrounded quickly by outer gases.
Humans discovered Neptune due to observations made by several astronomers on the perturbed orbit of its neighbor Uranus' orbit. The planet was officially discovered in 1846, but not without some controversy as to who actually discovered the planet.
Neptune was initially visited by Voyager 2 in 1989 and it wasn't until the Great Solar System Tour that any spacecraft ever journeyed back.
The first colony established on any world orbiting Neptune was on Triton in 2390 in order to study not only the moon itself but the planet as well.
As with the creations of dirigible cities in other gas giants, Neptune eventually began constructing their own floating cities within the frigid atmosphere. By the year 10000 CE there were dozens of small floating continents and thousands of smaller cities.
in 15978 CE, Project Encase Neptune began, Stage One of which would connect the floating continents and cities into one giant mass beneath the initial layers of the planet's own atmosphere. Stage One was completed in 16102 CE.
Stage Two began two years after stage one was complete, and involved the mass construction of more floating continents connected to the initial major continent. Over the next fifteen hundred years, more "land" was constructed by importing Kuiper Belt objects for materials. Domes were constructed around the continents, creating a large interweaving construction of domes. Stage Two was completed in 17648 CE.
Stage Three involved the introduction of life within the new continents. Each dome was artificially heated and had been designed for many different kinds of microclimates. Stage Three lasted only around fifty years, completed in 17702 CE.
Since then, Neptune has been the shining example of the complete biodome-terraforming of gas and ice giants.
Neptune is a major tourist hotspot, especially for skiing on the artificial slopes of the mountain biodomes.