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Despite the lack of empirical evidence, the hypothesized existence of a liquid water ocean beneath the icy surface of Europa is supported by enough indirect data—photographic, spectroscopic, magnetic, and gravitometric—to make the proposal plausible [Gaidos and Nimmo, 2000; Greenberg, 2002; Kivelson et al., 2000; Prockter and Pappalardo, 2000]. A number of planetary scientists have suggested that were a Europan ocean to exist, it could be inhabited, if only by primitive microbial organisms [Chyba and Phillips, 2002; Gaidos and Nimmo, 2000; Greenberg, 2002; Kargel et al., 2000; McKollom, 1999]. We argue that speculation concerning potential habitability, unlike the Europan ocean hypothesis, is data-deficient. Engaging as this speculation may seem, a greater measure of caution should be exercised when elaborating a supportive framework of arguments.