This story was corrected on 4 March 2009.
27 February 2009—For centuries, humans have looked up at the sky and wondered if they were alone in the universe. Now we’re one step closer to finding an answer. On 6 March, NASA’s first planet-hunting spacecraft, Kepler , will embark on a three-and-a-half-year journey in search of Earth-like planets outside our solar system. Kepler is the first space telescope capable of discovering such planets orbiting in a distant solar system’s habitable zone—the area in which liquid water, and possibly life, can exist.
”We’re at the threshold of answering questions that date back to the ancient Greeks,” says James Fanson, Kepler project manager at NASA’s Jet Propulsion Laboratory, in Pasadena, Calif. Although astronomers have found more than 330 planets in other solar systems, none of these planets have the size and location believed necessary to support life.
Named for the 17th-century astronomer who discovered the laws of planetary motion, Kepler will orbit the sun instead of the Earth. The craft will focus on about 100 000 stars between the Cygnus and Lyra constellations. (To find this area, in the Northern Hemisphere, look for a triangle of the three brightest stars in the summer sky, which make up the Cygnus constellation. If you make a square with your hands and hold them at arm’s length in the direction of the constellation, you’ll see the area Kepler will explore.) Kepler will find planets using the ”transit method,” looking for periodic slight dips in the brightness of stars that can signal a planet orbiting a star.
” Kepler was a technically difficult challenge,” Fanson says. It took nearly 25 years to go from a far-off dream to reality. The mission is the brainchild of Bill Borucki, Kepler ’s principal science investigator at NASA Ames Research Center, at Moffett Field, Calif. ”Bill proposed the mission several times, but the reviewers were skeptical,” Fanson says. ”When an Earth-size planet passes a star, brightness only dims by 84 parts per million. Many thought the technology wasn’t available to measure that, and it took years for scientists to prove it was possible.”
”We didn’t have the detector technology 25 years ago to make those kinds of measurements,” says Riley Duren, chief engineer for Kepler . But in the past decade, charge-coupled devices (CCDs) with the parameters needed for finding other Earths have been demonstrated in the laboratory. Kepler uses the latest detectors but didn’t require inventing new technologies. ”We didn’t have to reinvent the wheel,” says Duren. ”We just took the best CCDs and made custom versions, and then we built custom electronics and software to get the most out of our system.” The result? A telescope that’s the equivalent of a 95-megapixel camera—the largest ever flown in space—made up of 42 CCDs, each with a bit more than 2 megapixels.
Ball Aerospace & Technologies Corp., in Boulder, Colo., the contractor responsible for building Kepler , began work on the US $500 million mission in 2002. The engineers had to face many challenges: keeping the camera pointed accurately enough so that the stars remained motionless in the images, creating a large field of view to increase the chances of finding stars with orbiting planets, and implementing low-noise electronics to make it possible to read data from the CCDs, according to John Troeltzsch, Ball Aerospace program manager for civil space systems.