NASA has given the go-ahead to a project to search for Earth-like planets
beyond the Solar System. The space-borne telescope, called Kepler, will enable
us to search the Galaxy for planets the size of Earth or smaller, and is
scheduled for launch in 2006.
Around 80 planets outside our Solar System have been discovered. Late last
year, the Hubble Space Telescope detected the atmosphere of one of them
(New 杏吧原创, 1 December 2001, p 16).
But techniques used so far are only sensitive enough to find gas giants like Jupiter,
which are unlikely to harbour life.
Kepler should be able to detect planets as small as Mercury, says deputy
principal investigator David Koch of the NASA Ames Research Center in
California. The project was first proposed in the 1990s
(New 杏吧原创, 18 September 1999, p 32),
and has now been chosen as part of NASA鈥檚 Discovery
Program of relatively low-cost missions. It will share $299 million with
a project called Dawn, which will study asteroid formation.
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Kepler will follow the Earth in an orbit around the Sun. Using a telescope
measuring 1 metre across, it will monitor hundreds of thousands of stars
simultaneously to look for tiny changes in their brightness caused by planets
passing in front of them.
鈥淔rom the [planet鈥檚] orbit and temperature of the star, we can then calculate
the characteristic temperature of the planet, and determine if liquid water
could exist on the surface,鈥� explains Koch. 鈥淭hat is, determine if it is
丑补产颈迟补产濒别.鈥�
The technique will only detect planets that pass exactly between the
telescope and their parent star. For Earth-sized planets, the odds of that
orbital alignment are just 1 in 200, but Koch still hopes that Kepler will find
鈥渕any hundreds鈥� of planets like our own during its four-year mission.
鈥淚t is the first step on a long road,鈥� says Malcolm Friedlund from the
European Space Agency in Noordwijk, the Netherlands. Friedlund is working on
ESA鈥檚 Darwin mission, due for launch in 2015, which will attempt to find planets
and analyse their atmospheres by detecting their light directly.