Plutonium is a heavy radioactive element. Pu-239 can be used in nuclear reactions. When SG-1 traveled to K'Tau via the Stargate, some plutonium piggy-backed onto their wormhole, and was deposited into K'Tau's sun, causing it to shift to the red light spectrum. SG-1 attempted to use a heavier element, HU-2340, to reverse the reaction. (SG1: "Red Sky")

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