Unorthodox Telescope for Alien Planet Hunt?

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For years, astronomers figured they’d need the combined light-gathering power of an array of telescopes in orbit to find Earth-like worlds, a daunting prospect since the armada would have to synchronize their flying to within a few nanometers.

But a team in Toulouse, France, believes there’s another way.

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Traditional telescopes have a mirror or a system of lenses to gather light from distant stars to produce astronomical images. Another option is to take advantage of how light bends, or diffracts, when it encounters an obstacle in its path.

So-called Fresnel imagers, named after early-19th century French engineer and physicist Augustin-Jean Fresnel, could be a handy tool in the hunt for extrasolar worlds, say scientists with the Observatoire Midi Pyrénées, which has been testing a ground-based prototype.

They figure a 30-meter observatory could detect planets the size of Earth within about 30 light-years. More important, since the imager is made of lightweight, foldable metal foil, it would be much less expensive to carry into orbit.

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Rather than a fleet of telescopes, the Fresnel imager is a two-spacecraft system. One contains the foil which is punched with precisely positioned patterns of holes to route the light. The second spacecraft flies at the focal point with a special lens, camera and other instruments to record observations. The pair would need to formation fly, but not nearly as precisely as the proposed Terrestrial Planet Finder array, for example.

A Fresnel imager mission proposal has been submitted to the European Space Agency for consideration.

Image: A proposed light-bending system to seek out Earth-like worlds. Credit: Observatoire Midi Pyrénées

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