Arkaylia

From Flash Gordon Wiki

Arkaylia is the name of one of two artificial moons that orbit the moon of Mongo. Along with its brother moon Surd, it was created pre-Sorrow for the use of shelter for travelers that came to mine the moon for its riches. Arkaylia was also used as a place to process the ore that came from the moon.

Immediately after The Great Sorrow, a group of Mongo inhabitants were chosen to leave the planet and live on Arkaylia. And they did so for three generations before going back to live on Mongo.