Regula

A Class D body according to the planetary classification, Regula was a remote planetoid within Federation space located close to the Mutara Nebula. Regula was orbited by the Federation research outpost Regula I.

According to Captain Spock of the USS Enterprise (NCC-1701), 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. 

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