Isaac Asimov once defined life as a localized preservation of low entropy with the assistance of enzymes. If we as a species are going to seek out other life forms we're going to have to expand the "enzyme" part of the definition a bit. Enzymes are proteins that serve as chemical catalysts. Let's not assume that the mechanisms for life on Mars or Saturn's moon are the same as the mechanisms with which our biochemists are familiar. Thus, I propose that for the our purposes we could understand life to be the localized preservation of low entropy through sustained chemical catalysts. Science fiction aficionados are of course familiar with speculations that silicon would work, as an alternative to carbon, as a means by which phenomena worth considering life could be sustained. Silicon based life would require catalysts that would not be proteins, i.e. not enzymes. Heck, there was an episode of the (original) Star Trek devoted to this precise point, and the spe...