902 Encyclopedia of the Solar System
FIGURE 14 Artist conception of the Kepler photometer and
spacecraft.A 1 m Schmidt telescope will observe a large section
of the sky in the constellation Cygnus continually for over 4 years
to detect transits of Earth-sized planets in Earth-like orbits
across the disks of solar-type stars. Launch is scheduled for late
- (Image courtesy NASA Kepler project.)
photometry spacecraftCOROTin 2006. WhileCOROTwill
not be able to detect the transits of Earth-size planets, it will
be able to detect transits of Neptune-size bodies.
The most complex and ambitious space mission is the
Terrestrial Planet Finder. This mission is designed not only
to directly image Earth-like planets in the habitable zones
of nearby stars, but also to look for the tell-tale signs of an
active biosphere on these worlds. NASA has just recently
decided to proceed with a two-stage TPF plan: to launch
first a large optical telescope equipped with an advanced
coronagraph (TPF-C) and then later a more powerful ar-
ray of infrared space telescopes using interferometry (TPF-
I, Fig. 14). Also DARWIN, a mission currently planned
by ESA, will be using a space-based infrared interferom-
etry array. These space telescopes will have the capabil-
ity not only to take direct images of terrestrial planets in
the habitable zones of other stars but also to perform first
crude spectroscopic follow-up observations of these plan-
ets. The spectra of these extrasolar Earths should allow us to
determine the chemical composition of their atmosphere.
This will allow us to determine if water vapor is abundant,
suggesting a planet with oceans, or if green house gases
are present, warming the planet by the greenhouse effect.
Of particular interest will be whether the spectra also in-
clude so-called biosignatures, like absorption by molecu-
lar oxygen (or ozone) or methane. These gases are unsta-
ble and short-lived and need to be replenished, which, at
least in Earth’s case, is done primarily by photosynthesis
in living organisms. Thus, TPF and DARWIN are planet-
finding missions that will even have the potential to answer
the eternal question:Does life exist somewhere else in the
cosmos?Bibliography
Boss, A. (1998). “Looking for Earths: The Race to Find New
Solar Systems.” Wiley, New York.
Clark, S. (1998). “Extrasolar Planets: The Search for New
Worlds.” Wiley, Chichester, United Kingdom.
Croswell, K. (1997). “Planet Quest: The Epic Discovery of
Alien Solar Systems.” The Free Press, New York.
Mayor, M., and Queloz, D. (1995) A Jupiter-mass companion
to a solar-type star.Nature 378 , 355.