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Comet displays are thought to be due to sublimation of volatile ices from an inert nucleus in the heat of the Sun. For example, the Stardust mission has shown that the origin of comets requires some high-temperature conditions. A 'cross-eye' stereo pair of comet Wild 2's nucleus showing typical EDM erosion. Comet flybys have shown phenomena of great complexity and higher energy than expected. Comet Hyakutake showed unsuspected high-energy processes taking place in the comet. A forbidden oxygen spectral line in the coma of Comet Austin pointed to an intense electric field. Activity is restricted to small areas on each comet nucleus and takes the form of collimated jets, which maintain their filamentary coherence across tens of millions of kilometers. The complex structure and high-energy behavior can be explained if the comet is a charged body moving in a radial electric field responsible for accelerating the solar-wind plasma, rather than an inert, heated body in a rarefied supersonic "wind." The jets and surface topography of comets are consistent with EDM erosion of a cathode surface. The fine dust particles may be the result of cathode sputtering. The presence of the OH radical may be due to combination of sputtered negative oxygen ions from the comet nucleus with solar 'wind' protons and is consistent with the lack of water ice observed on comet nuclei. On the basis of an electrical theory of comets, the author predicted that the Deep Impact mission would observe an electrical flash before impact with the copper projectile and that the outburst would be more energetic than expected.