A planet whose inhabitants were accelerated by radiation and natural disaster, leaving them living at a speed beyond normal perception.
Scalos is the homeworld of the Scalosians. Volcanic activity released radiation that accelerated the population and killed most of them, and left the surviving men sterile. The survivors' cities are empty in normal time.
In Wink of an Eye, the Enterprise answers a distress call from Scalos and finds no one there. The Scalosians then board the ship, seeking new mates. At the end, Kirk returns them to their planet.