The electron-microscope analysis of the Orgeuil carbonaceous chondrite, thought to be the extinct core of a comet, shows many archaen microfossils adapted for both cold and hot liquid water environments. Since water is a prerequisite for life, its presence on a comet would have important implications for interplanetary cross-contamination of the planets as well as strongly impact the dynamics and evolution of a comet. Therefore we develop a wet comet model to explore the consequences of liquid water on Mars-crossing comets and hypothesize that all the periodic comets, such as P/Halley, P/Wild-2, and P/Borrelly show signs of significant liquid water processing. The wet comet model is shown to be compatible with observation, as well as provide significantly better explanations for well-known cometary anomalies. Finally, the model predicts that the results of both Rosetta and Deep Impact missions will deviate from expectations.
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