Searching for Earths
If you have to stare at one spot in the sky for more than three years, the region between the bright stars Vega and Deneb isn't a bad choice. The region encompasses part of the Milky Way -- the faintly glowing disk of our home galaxy. And many of the stars in that band are similar to our own Sun.
In fact, that's where the Kepler spacecraft is looking right now. It was launched in March, and completed its checkouts in May.
Its goal is to find Earth-like planets in Earth-like orbits around Sun-like stars. Such planets are the most likely candidates for Earth-like life.
Kepler will stare non-stop at a hundred thousand stars in that region over the next three years. The stars are in the constellations Lyra and Cygnus, which are high overhead at nightfall. Kepler's starfield is centered between Vega and Deneb.
Kepler will watch for transits, which occur when a planet passes across the face of its star, blocking some of the star's light. Earth-like planets in Earth-like orbits will produce only a small drop, which lasts only a few hours. But the drop should repeat itself a few times during Kepler's mission, allowing scientists to measure the planet's size and orbit -- parameters that will tell us if it could have liquid water and a life-supporting atmosphere.
Scientists expect Kepler to find perhaps 50 Earth-like planets -- the prime targets for future searches for signs of life.
More about Kepler tomorrow.
Script by Damond Benningfield, Copyright 2009
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