In Finding Other Worlds, Edna DeVore of the SETI Institute zeroes in on the importance of the Kepler Mission. Scheduled for an October 2007 launch, Kepler is likely to discover hundreds of extrasolar planets. And as DeVore writes, “Kepler is the first observatory capable of finding Earth-size worlds in the habitable zone of distant Suns. In other words, Kepler may find ‘good places to live.'”
Some key points about Kepler:
To find planets, the mission will use the transit method, looking for the dimming of a star caused by repeated transits of a planet across its face.
The size of a planet can be calculated from changes in the star’s brightness, and the size of its orbit can be measured.
The parameters of the mission are the most challenging ever attempted for extrasolar detection. Kepler is designed to survey nearby stars to determine how often terrestrial and larger planets occur in the habitable zone of different types of star. This, in turn, will allow the follow-on Space Interferometer Mission (2010) to target systems already known to have terrestrial planets.
By ‘habitable zone,’ the Kepler scientists mean the distances from a given star where liquid water can exist on the planet’s surface.
The changes in brightness to be measured are vanishingly small. According to NASA, “Transits by terrestrial planets produce a fractional change in stellar brightness of 5 x 10-5 to 40 x 10-5 lasting for 2 to 16 hours. The orbit and size of the planets can be calculated from the period and depth of the transit.”
Kepler will test two hypotheses: that most main sequence stars have terrestrial planets in or near the habitable zone, and an average of two Earth-sized planets form in the region between 0.5 and 1.5 AU (based on our own Solar System, and what we now believe about planetary formation).
We now know about approximately 130 planets around other stars, a number which should increase enormously by 2007. But Kepler will likely be the first chance at detecting terrestrial worlds, paving the way for the Terrestrial Planet Finder mission that will study such planets in detail. For more on the mission, see NASA’s Kepler page.
