Anti-quark energy was obtained from anti-matter. Professor Sorenson, who had dedicated his career to finding alternative energy sources, believed that anti-matter minerals from Zeta Minor would provide the necessary anti-quark energy to re-fuel the Morestran sun. The Fourth Doctor believed there was no practical way to exploit it. The presence of the minerals on a Morestran probe ship prevented it from escaping Zeta Minor's gravity. Only when they were jettisoned — and the prospect of using anti-quark energy abandoned — was the craft able to leave. (TV: Planet of Evil)

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