[Spock is preparing to enter the radiated warp core.]
Dr. McCoy: Are you out of your Vulcan mind? No human can tolerate the radiation that's in there!
Spock: As you are so fond of observing, doctor, I am not human.
McCoy: Are you out of your Vulcan mind?!
Saavik: You lied!
Spock: I exaggerated.
Chosen answer: According to the novelisation of the film the Genesis project was initially designed to be capable of creating an entire solar system. While the focus of the project eventually narrowed down to altering an individual planet, the sub-routines necessary to create a star were still in place and were activated when the device detonated within the nebula.
Tailkinker ★