After more than four years in space, restlessly searching for
planets orbiting other stars, NASA’s Kepler space telescope may
have met its demise. The Kepler project is typically described
in terms of raw numbers. As of the last official announcement,
it had found 2,740 likely new planets–including 1,200 Neptune-
size planets, 350 Earth-size planets, and at least 4 planets
that orbit within the “habitable zone” where liquid water can
exist. All of those numbers are sure to increase, as more
observations are confirmed and as mission scientists continue to
dig through a trove of archived data. But spirit, not
statistics, is what really defines Kepler. It is a modern
version of the expedition of Lewis and Clark, or the great
voyages of Vasco da Gama and Ferdinand Magellan. It is a
headlong plunge into the unknown cosmic territory around us.
Extrapolating from Kepler’s results, astronomers now estimate
there are at least 17 billion Earth-size planets in our galaxy.
That is another number, yes, but one with a power