Imaging Earthlike Exoplanets

Two space missions now under development aim to uncover sister worlds to our own

Thomas Sherrill

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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