In the mirror universe, Rigel XII was a barely habitable planet that suffered from intense storms.
Under the control of the Terran Empire, Rigel XII was home to several hundred miners who extracted lithium. Although lithium had ceased to be used in warp engines by the 2260s, imperial scientists still used it to power many devices. Moreover, there were several research bases clustered around the mining encampments. The researchers stationed at these bases were protected by Science Ministry Security teams.
The largest base was owned jointly by the Ministry and Keeler Aerospace. Rumors persisted throughout the empire that the base was working on super-weapon or planet destroyer. In fact, rumors were so prevalent that it attracted the attention of several foreign governments. A trio of surgically-altered Romulans was arrested on Rigel XII. Even the Cardassian government offered half a billion credits for schematics on the alleged planet destroyer. (ST module: Through a Glass, Darkly)