Are we not the only Earth out there?

Kepler Cacophony
Kepler-22's star system. Think we'll ever make it there?
Kepler-22's star system. Think we'll ever make it there?
Image courtesy NASA/Ames/JPL-Caltech

One of NASA's most celebrated programs relies on the transit method to find exoplanets. Since 2009, the Kepler mission's space telescope has been surveying 170,000 stars in a small patch of sky near the constellations Cygnus and Lyra. Its main instrument, a photometer with a field of view of just 12 degrees, can detect stellar dimming caused by planets as small as Earth.

So far, its observations have rocked the scientific community and stirred the imaginations of space geeks everywhere. In all, the mighty Kepler has identified more than 3,000 potential and confirmed planets. Those that have been confirmed could be entries in an atlas of the "Star Wars" galaxy. For example, Kepler-16b is a Saturn-sized planet orbiting two stars, a la Luke Skywalker's home Tatooine. And the Kepler-11 system consists of six planets -- some rocky and some gas giants -- orbiting a single, sunlike star.

The most amazing discoveries, however, occur when astronomers confirm the existence of Earth-like planets, such as the two dubbed Kepler-20e and Kepler-20f. Both are terrestrial planets roughly the same size as our own inner planets. Kepler-20e is slightly smaller than Venus, and 20f is slightly larger than Earth. Unfortunately, neither of these potential Earths lies in the Goldilocks zone -- both are burning-hot ovens -- so they're unlikely to harbor little green men, or even little green microbes. Kepler-22b may be more hospitable. Confirmed in December 2011, 22b is located 600 light-years away and orbits in the Goldilocks zone of a sunlike star. Astronomers believe the planet's radius is more than double that of Earth, but they haven't determined its composition.

Kepler isn't the only effort uncovering a bonanza of awe-inspiring exoplanets though.