NASA's resurrected telescope seeks wandering planets

Kepler will use "gravitational lensing" to spot Milky Way exoplanets.

NASA is kicking off a search for free-spirited exoplanets as part of the Kepler space telescope's extended K2 mission. It's an impressive quest for an instrument that was all but written off several years ago because of damage to its control wheels. NASA managed to stabilize the device using radiation pressure from the sun and it's been spotting exoplanets, stars and galaxies ever since. Now, the space agency wants to use the device to survey millions of stars in the Milky Way galaxy looking for signs of "wandering" exoplanets with no companion star.

Astronomers think there may be more free-range planets in our galaxy than stars, but finding them isn't easy since they don't regularly block starlight like orbiting planets. To help, scientists will use a phenomenon called micro-gravitational lensing. A passing planet's gravity causes a star's light to bend, making it appear brighter for several days. The amount of deflection and brightening caused by such planets is small (hence "micro-gravitational"), but Kepler can spot it. "We are seizing the opportunity to use Kepler's uniquely sensitive camera to sniff for planets in a different way," said NASA researcher Geert Barentsen.

Because Kepler is 100 million miles from Earth, scientists will use ground-based satellites to observe the same stars from a slightly different angle. The resulting "parallax effect" should yield additional information about expolanets and stars. Kepler will also be flipped around so that it can be observed from Earth at the same time it observes the sky. That will give it a unique opportunity to snap the Earth and moon as they cross its field of view on April 14th. Once it's cleaned up and processed, the snap will be released to the public in June.

NASA is also using the mission as a test run for its Wide-Field Infrared Survey Telescope (WFIRST). That satellite, launching in the 2020s, will also use micro-gravitational lensing to spot planets, but on a much larger scale. Kepler will stand on its own, however, as scientists expect to spot 10 or more expolanets in 80 days. "The chance for the K2 mission to use gravity to help us explore exoplanets is one of the most fantastic astronomical experiments of the decade," says NASA Kepler scientist Steve Howell. Not bad for an instrument that finished it's primary mission in November, 2012.