Pluto

Pluto is a dwarf planet in the outer Sol System.

Physical characteristics
Pluto lies in the outer Sol System at a distance ranging from 29 to over 40 astronomical units from Sol. It's orbit is extremely elongated, as for many Kuiper Belt objects, making extremely short summers and eternal winters. Pluto stays out of Neptune's way as the two planets orbit just a couple of astronomical units from eachother at their closest point to each other. Pluto can actually come closer to Sol than Neptune does sometimes.

Due to the planet's extremely eccentric orbit, the temperatures vary from 45 K to 30 K. A substantial atmosphere only forms when Pluto is at its perihelion point. This atmosphere is dangerous to living organisms as it is made of greenhouse gases. When Pluto is at its aphelion, the atmosphere does not exist as we know it. Instead, it blankets the surface as "snow".

Despite its hostile environment, Pluto has a lot of colonies. All of them are Human, but a lot of them are inhabited by other species. Travel at light speed from Pluto to Earth would take just over five and a half hours.

The largest of these colonies is Nexus City, with a population of 879,000.

Pluto's enviroscore is at least 77, having a population of over 5.5 million.

Pluto also contains three moons, Charon, Nix and Hydra. Charon is merely half the size of Pluto, because of that Pluto is considered a double planet. Nix and Hydra are captured asteroids and orbit much farther than Charon does.

History
Pluto was probably seen in early times, but wasn't identified until 1930, when a Human astronomer called Clyde Tombaugh discovered it with his telescope. The newly found object was named "Pluto" after the god of the underworld by a girl called Venetia Burnley.

Considered as the ninth planet of the Sol System until 2006, Pluto was taken off the list of planets in that year. Along with a similar, but much further object called Eris and the relatively close to Earth Ceres, Pluto was put in the new "dwarf planet" category.

In the mid 22nd century, Pluto was explored by Humans. These Humans found bases which later expanded over the years and have survived until this day. Because of its actual age, Nexus City has been extensively renovated over the past few years.