Stars shine so brightly that any planets orbiting them are lost in the glow. In fact, astronomers can only detect exoplanets indirectly by their effects on parent stars: either gravitational or, as the planet passes in front, by dimming. But a 50-meter-wide, daisy-shaped star shade could block stellar light, allowing direct observation of their planets, according to a new paper in today's Nature.

Webster Cash of the University of Colorado designed the star shade to be used in conjunction with orbiting telescopes. The thin plastic shade would cancel out a specific star's light and the telescope--trailing 15,000 miles behind--could then take in light from its distant planets. "Think of an outfielder holding up one hand to block out the sunlight as he tracks a fly ball," Cash explains. "We would use the star shade as a giant hand to suppress the light emanating from a central star by a factor of about 10 billion."

The shade's daisy shape allows a small amount of a star's light to diffract around it at the base of each petal. Its attendant planets then appear as faint stars. Tested on our own solar system in a simulation, the star shade reveals Earth, Mars and Jupiter from a distance of seven parsecs. Thus far, only exoplanets as small as Neptune have been detected using current methods. "We will be able to study Earthlike planets tens of trillions of miles away and chemically analyze their atmospheres for signs of life," Cash says.

The star shade and its attendant telescope would orbit Earth at a distance of roughly one million miles, using thrusters to keep the shade precisely positioned. Cash and his team have proposed to include such a system to work with the James Webb Space Telescope--an infrared observatory scheduled to be launched in 2013--and note that technology to build such a shade already exists and would not be extremely expensive. "If Earthlike planets around the nearby stars do exist, use of an occulter could find them within the next decade," Cash wrote in the paper. "There is a bit of Buck Rogers in the New Worlds Imager concept," he adds. "But seeking and mapping new lands is something that seems to ring deep in the human psyche."

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