NASA's Kepler, launched a little more than a year ago, follows in the Earth's wake as it orbits the Sun -- its sights focused permanently on a single patch of sky. With its unblinking gaze, the spacecraft searches among 156,000 stars for slight but regular dips in a star's brightness. Such dimmings could indicate a transit - a planet moving across the face of its home star. If scientists' expectations prove true, over its three and a half year mission, Kepler could discover hundreds or perhaps thousands of transiting exo-planets.