NASA's Kepler telescope will stare at the sky searching for planets beyond the solar system through 2016 after the space agency extended the mission on the advice of the astrophysics research community.

Artist's concept of the Kepler spacecraft. Credit: NASA
 
Kepler's primary mission was due to end in November 2012, but an independent panel of senior scientists gathers every two years to study NASA's operating research missions, issuing recommendations on whether the projects should continue to receive funding.

"The Kepler mission is an outstanding success," the senior review said. "Kepler is not only a unique source of exoplanet discoveries, but also an organizing and rallying point for exoplanet research. It has enabled remarkable stellar science."

The senior review recommended Kepler be continued through 2016.

"Kepler has revolutionized our understanding of exoplanets and the study of stellar seismology and variability," said Roger Hunter, Kepler project manager at NASA's Ames Research Center in Moffett Field, Calif. "There is currently no other mission in development that can replace or surpass the precision of Kepler. This extended mission will afford Kepler a unique opportunity to rewrite our understanding of the galaxy and our place in it."

Launched in March 2009, Kepler is stationed in an Earth-trailing solar orbit and aims its 3.1-foot telescope toward constellations Cygnus and Lyra, observing a 10-degree-wide field containing 4.5 million detectable stars. Kepler is focusing on approximately 156,000 stars for the purposes of its research.

The observatory monitors the stars for dips in brightness, an indication a planet could be passing in front of it. Three transits are required to verify a planet, according to NASA.

Artist's concept of Kepler-22b, the first planet found in a star's habitable zone. Credit: NASA
 
After following up with other observatories, researchers have confirmed 61 new exoplanets detected by Kepler. The discoveries include the first rocky exoplanet, the first Earth- and Mars-sized extrasolar planets, and the first small planet in another star's habitable zone, the distance at which liquid water could exist.

Kepler has identified multi-planet solar systems and planets circling two stars.

According to Kepler scientists, the mission detected more than 2,300 planet candidates between May 2009 and September 2010. Nearly 40 percent of the potential discoveries are less than twice the size of Earth.

The data show 46 candidates in their host star's habitable zone.

While many of Kepler's earliest confirmed planets were enormous gas giants circling too close to a star for life, more planets further from their parent stars could be confirmed as the mission continues.

Because Kepler must observe a transiting planet several times before confirming a discovery, it can take several years for scientists to collect enough data to announce a planet in the habitable zone.

One of Kepler's objectives is to estimate the number of potentially habitable exoplanets. According to the senior review, Kepler observations need to continue until at least 2015 to achieve the goal.