Three planets, Sigma Draconis III, Sigma Draconis IV, and Sigma Draconis VI, were classified as M class and populated by native species. The other planets in the system - Sigma Draconis I, Sigma Draconis II, Sigma Draconis V, Sigma Draconis VII, Sigma Draconis VIII, and Sigma Draconis IX - were not M-class. There were surveys and long-range scans of this system. Information on the system was stored in the library computers of Federation starships. In 2268, the USS Enterprise entered the system to search for Commander Spock's brain. (TOS: "Spock's Brain" )