U.V.6, also simply known as Planet UV, or Planet 6, is an icy planet in the Frigido star system. Uninhabited by humans and/or other humanoids, virtually in the middle of nowhere.
The extremely harsh environment (ranging from tundra-like to sub-polar, much like Earth's natural Poles) is life-sustaining to very few species of wildlife, and most are predatory. The planet is indicated by Toombs to be called "U.V.6" as more of a joke, " 'cause even the sun can barely stand the weather ".
Richard B. Riddick made his home in a cave for approximately 5 years, which was actually the carcass of a large whale-sized carnivorous creature. It has several rows of talon-like teeth surrounding its open maw. Riddick was hiding there in order to protect Jack from being hunted as his accomplice; until he was found by Toombs and his crew of Mercs. Toombs was the known only survivor of the encounter, and was stranded there when Riddick left U.V.6 with Toombs' ship.
Toombs' commentary on this planet was as follows: "If the cold doesn't bite into you and make you bleed, the hairy-ass monsters on this planet sure will. They call it Planet UV, 'cause even the sun can barely stand the weather. It's the last place I'd go lookin' for most cons, and I've been to plenty of shithole planets in my day. But if the bounty is high and the intel is solid, I guess I'd go just about anywhere."
According to the David Twohy there were originally Mercs searching for Riddick on foot on U.V.6, however these scenes were cut from the theatrical and the Director's Cut. These screen shots are from the visual effects company from The Chronicles of Riddick.