Centauri's Thoughts

The Kepler mission is due to launch next week (March 6th)

It is the first mission with the ability to find planets like Earth -- rocky planets that orbit sun-like stars in a warm zone where liquid water could be maintained on the surface. Liquid water is believed to be essential for the formation of life.

"Kepler is a critical component in NASA's broader efforts to ultimately find and study planets where Earth-like conditions may be present," said Jon Morse, the Astrophysics Division director at NASA Headquarters in Washington. "The planetary census Kepler takes will be very important for understanding the frequency of Earth-size planets in our galaxy and planning future missions that directly detect and characterize such worlds around nearby stars."

The Kepler spacecraft will watch a patch of space for 3.5 years or more for signs of Earth-sized planets moving around stars similar to the sun. The patch that Kepler will watch contains about 100,000 stars like the sun. Using special detectors similar to those used in digital cameras, Kepler will look for slight dimming in the stars as planets pass between the star and Kepler. The Kepler's place in space will allow it to watch the same stars constantly throughout its mission, something observatories like Hubble cannot do.

The method used will be the “transit” method (star-crossing orbit). We have seen venus do this: here and here.

Of course, this method wont detect every planet orbiting a star, because the planet must pass directly in front of that star, and given solar systems random alignment compared to ours, the Kepler mission is figuring lower odds for detection. But given the large survey sample (100,000) they feel that the number found will tell us more about how common planets are in other solar systems.

References and more reading:
Keplers Home Page

space.com article

Scientific American Article