Although solar panels will work on spacecraft at that distance, the desire for sufficient energy to drive many instruments means any mission would really need to go with radioisotope thermal generators (RTGs) - solid state electrical generators powered by the heat of radioactive decay.

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The enormous heat generated by the radioactive fuel in the reactor core needs a constant flow of cold water.

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Once the reactor has shut down, there remains "decay heat" from traces of other radioactive isotopes.

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Thermoelectric coupling uses heat from the decay of a radioactive fuel (as opposed to the full-scale nuclear fission which powers a reactor on Earth) as its energy source.

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Some geologists falsely believed heat from the waste could melt surrounding rock and form a radioactive volcano.

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The heat that keeps the core of the earth molten is primarily radioactive decay -it is what makes rock into liquid lava.

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