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WASHINGTON, DC - JULY 14: Sara Seager, professor of planetary science and physics at the Massachusetts Institute of Technology, speaks at a press conference discussing 'the scientific and technological roadmap that will lead to the discovery of potentially habitable worlds among the stars' July 14, 2014 at NASA headquarters in Washington, DC. Most prominent among the methods NASA will search the universe for habitable exoplanets will be the deployment of the James Webb Space Telescope, with a mirror of 21 feet, scheduled to be launched in 2018. (Photo by Win McNamee/Getty Images)

WASHINGTON, DC - JULY 14:  Sara Seager, professor of planetary science and physics at the Massachusetts Institute of Technology, speaks at a press conference discussing 'the scientific and technological roadmap that will lead to the discovery of potentially habitable worlds among the stars' July 14, 2014 at NASA headquarters in Washington, DC. Most prominent among the methods NASA will search the universe for habitable exoplanets will be the deployment of the James Webb Space Telescope, with a mirror of 21 feet, scheduled to be launched in 2018.  (Photo by Win McNamee/Getty Images)