A U.S. orbiting telescope designed to help answer one of the oldest and deepest questions of astronomy regarding our being alone in the universe or not, is scheduled to launch Friday. The Kepler Spacecraft will spend the next three and a half years monitoring 100,000 stars for variations in brightness that could be caused by an orbiting planet.

These planets are too small and too difficult to be seen with past telescopes. But they are precisely the kinds of planets on which life could exist.
Kepler is NASA's $600 million telescope, scheduled to launch from the Kennedy Space Center. Its potential is enormous, according to astronomer Debra Fischer of San Francisco State University.

"What excites me is for the first time, we are going to have a mission that can take a full census of the kind of planets that exist around other stars," she said. Jon Morse, NASA's top astrophysicist, believes Kepler will revolutionize what we know about the universe.
Kepler will use an unprecedented combination of light detectors (adding up to about 95 million pixels) to capture the subtle shifts in light that characterize an extrasolar planet orbiting its star.

Over the last two decades, scientists have spotted more than 300 extrasolar planets circling other stars in our Milky Way galaxy. Most of these planets have been about the size of Jupiter or larger, making it unlikely they would harbor life. But those aren't what Kepler is aiming to find. Its targets are planets like Earth, rocky planets in an orbit where life might be possible, according to the principal investigator for Kepler science William Borucki of NASA's Ames Research Center in Moffett Field, California.