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Astronomers have discovered nearly 200 planets orbiting distant
stars. The vast majority of these bodies are considerably more
massive than Earth, perhaps because of the inherent bias in the
methods used to detect such extra-solar planets. Distant worlds that
are more Earthlike in size and composition are likely to be abundant
too—just harder to detect. Astronomers have thus been intent
on developing the means to find Earthlike planets and to obtain
spectra of their atmospheres, which could show whether conditions
are amenable to life—and may even yield indirect evidence of
life itself. Of particular import in that regard is the planning now
going on for two space missions, both called Terrestrial Planet
Finder. One, slated to be launched in a decade or so, will involve a
single telescope outfitted with a coronagraph, a set of occulting
masks designed to reduce the glare of a distant star enough to
reveal planets that may be in the vicinity. The other, to be
launched a few years later, will use multiple telescopes configured
as an interferometer, which can suppress light from a star using the
phenomenon of destructive wave interference, while allowing light
from a planet near that star to be detected.
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