Planet located in the constellation of Skythra; it was part of the Cyrennic Empire. It was 116 parsecs away from Cyrennis Minima and three light centuries away from the Magellanic Clouds. It took 64 local years to complete its elliptical orbit around its sun, which meant that its seasons (Ice Time and Sun Time) lasted 32 years each. Because its civilization was still in the medieval stages, Ribos was classified by the Alliance as a Grade-3 planet, and was protected from alien interference. Its principal city was Shurr. Galactic con artists Garron and Unstoffe tried to sell Ribos for ten million opeks to the Graff Vynda-K, using a lump of jethrik which turned out to be a segment of the Key to Time for bait. Eventually, Garron and the Fourth Doctor joined forces to defeat the Graff, who perished in the Riban Catacombs (5A).