  Do We Inhabit The Best O All Possible Worlds? German mathematician Gottfried
Leibniz thought so, writing in 1710 that our planet, warts and all, must be the
most optimal one imaginable. Leibniz's idea was roundly scorned as unscientific
wishful thinking, most notably by French author Voltaire in his magnum opus,
Candide. Yet Leibniz might find sympathy from at least one group of scientists
- the astronomers who have for decades treated Earth as a golden standard as
they search for worlds beyond our own solar system. Because earthlings still
know of just one living world - our own - it makes some sense to use Earth as a
template in the search for life elsewhere, such as in the most Earth-like
regions of Mars or Jupiter's watery moon Europa. Now, however, discoveries of
potentially habitable planets orbiting stars other than our sun - exoplanets,
that is - are challenging that geocentric approach.
