Monday, March 24, 2008
Astrobiology gives a nice brief on the Kepler Space Telescope Mission expected to launch in next year in Febuary. The Kepler is designed to find extraterrestrial planets the size of the Earth, utilzing the "transit method", which finds an extrasolar planet by measuring the drop in brightness of a distant star when a planet passes in front of the star relative to Earth.
More on the Kepler Mission can be found from NASA found here.
"NASA’s Kepler mission, selected in 2001 as the agency’s tenth Discovery mission, is a space-borne telescope designed specifically to look for alien Earths. It is “NASA’s first mission capable of detecting Earth-size and smaller planets around other stars,” says David Koch, an astrophysicist at NASA Ames Research Center near Mountain View, Calif., and the Deputy PI on the Kepler project."
Kepler will be able to detect a drop in a star's brightness as low as one-hundredth of one percent - the difference between looking out a window in your house and looking out it while it is open is around one percent. The Kepler will be launched into an Earth trailing orbit to avoid the effects of the atmosphere, which can vary the amount of detectable light greatly exceeding the sensitivity of Kepler's instuments. Larger planets can be detected from the ground based telescopes, but the smaller worlds we seek do not "dip" the light from their parent stars enought to be detected, hence this mission.
The mission will be conducted over a period of four years, taking measurements of 10,000 stars every 30 minutes. Transits last for only a few hours at a time, so in order to detect one, a large number of stellar "snapshots" need to be taken in order fo discover them. Kepler will continuously examine the same part of the sky located between two of the northern hemisphere's brightest stars, Vega and Deneb. The first planets Kepler will discover will be those closest to their parent stars, and thus making the most transits.
The goal is to find a Earth size world making about four transits around a Sun-like star - making it quite likely to inhabit that star's habitable zone. There are around 5,000 such stars in the regions to be studied, but many possible planets may not lie in an oribital plane we will be able to see. The Kepler team expects to find around 50 such Earth type planets in a star's habitable zone. The mission is likely to find hundreds of other planets as well. 250 planets have already been found from ground based observations, many of them short period "hot Jupiters", gas giants that orbit very close the their stars.