All good things must come to an end, and this includes Kepler, a space observatory that revolutionized astronomy’s understanding of exoplanets in the Milky Way. NASA officials announced yesterday that Kepler’s positioning system broke in May and cannot be repaired so it will no longer be used to find planets. Though the observing phase of Kepler is at an end, learning what insights it has to offer scientists is just beginning.
"The Kepler mission is by no means over," said Paul Hertz, NASA's astrophysics director. "We expect the most exciting discoveries will come in the next years." Launched in 2009, the Kepler spacecraft was designed to observe Earth-like planets about 3,000 light years away that orbit in or near habitable zones around sun-like stars. These zones are regions where water can be liquid at least part of the time, which scientists believe is the basis for life. To find planets, Kepler used the transit method, which notes when planets move in front of their stars repeatedly, each time reducing the amount of light the telescope sees coming from the star.
The technique requires precise pointing to keep Kepler’s gaze dead on at about 100,000 target stars, a feat accomplished by three spinning wheels controlling the telescope's motion up and down and side to side. The craft needs at least three wheels to stay stable, and one of the four that Kepler possessed had already failed in July 2012. In May a second wheel fell into "safe mode," ending the telescope’s observing phase of the mission.
Its contribution to science, however, is just moving on to the next stage. Kepler has already detected 135 planets and identified more than 3,500 candidate planets. To be sure that a planet is responsible for any changes in the light coming from a target star, scientists needed Kepler to record three to four years of a planet's transit. Scientists still have over two years of archived data from Kepler to analyze.
NASA officials will decide whether or not to continue using Kepler for other missions such as observing asteroids, comets, supernovae, and some large planets in the galaxy. Budget for the Kepler project is currently at about $18 million a year.
"I'm confident that we are going to find what we expected ... but we're going to have to work hard for the next couple of years," said Kepler lead scientist William Borucki, also with Ames, referring to an Earth-sized planet hospitable to life.
Another mission is expected to take Kepler’s place in 2017. Named the Transiting Explanet Surveillance Satellite (TESS), this follow-up mission will search for larger and bright planets closer to our solar system.
The announcement comes as researchers at MIT have discovered an Earth-sized exoplanet named Kepler 78b that whips around its host star in a mere 8.5 hours — one of the shortest orbital periods ever detected.