The most massive dwarf planet in the Sol System, Eris (also Rupert and Xena) is a frozen dwarf planet beyond the orbit of Pluto on a 560-year orbit. It has one moon called Dysnomia, both discovered in 2005. It was first visited by space probes in 2062 to search for a suitable location on the dwarf planet for a human colony. It also is a very bright object in the sky.
Eris was discovered by Mike Brown, titled the Pluto Killer (for demoting Pluto's planetary status), Chad Trujillo and David Rabinowitz on the 5th January 2005. It was later discovered that Eris has only one moon, named Dysnomia, in a perfectly circular orbit, unlike Eris' orbit. Eris' discovery was not announced until 29th July 2005, a few months later, probably to confirm Eris' existence in the Kuiper Belt. Upon discovery, it was originally going to be named Xena, after Mike Brown wanted to name more objects after female deities.
At the time of the it's discovery, Eris was too far away to send a probe to, due to the technological limits of the early 21st century. Up until 2062, the first high resolution images of Eris were taken by probe making a close approach to the dwarf planet.
NASA, among other space companies, had launched the Kuiper Belt Exploration Program (KBEP) in 2045 to, obviously, explore the outer Solar System, including Pluto, Eris, Haumea, Makemake and Sedna. Several probes were sent to Eris between 2061 and 2064 to aid the final step: colonisation. A space station was placed into Eris orbit in September 2064 with a crew of five, monitoring oxygen levels, scans of Eris and Dysnomia and deploying rovers and landers to find the best spot on the ice world to setup a colony.
A manned mining station was sent to the surface of Eris to begin harvesting its ice, converting it into water for liquid fuel rockets, although warp drives were becoming mainstream for the human race.
Eris has one moon called Dysnomia, discovered at the same time as Eris. At roughly 684 km in diameter, it is home to less than a million humans. No other moons have been discovered since 2005.