Regula

Regula is a planetoid in the Mutara sector within Federation space, a Class D body according to the planetary classification. Regula is orbited by the research outpost Regula I.

According to Captain Spock of the USS Enterprise, Regula is "essentially a great rock in space".

It was later revealed that the research team developing the Genesis Device, led by Doctors Carol and David Marcus, had constructed a giant cave inside the planetoid, filled with various plant life and water. According to Carol Marcus, it had taken the Starfleet Corps of Engineers ten months to dig out the underground structure, while the matrix used to terraform the cave only needed a day to take shape. (Star Trek II: The Wrath of Khan)