Planets found by Kepler likely larger than thought

Since its launch in 2009, NASA's Kepler Space Telescope has spotted more than 2,700 potential exoplanets, and a new study suggests those alien worlds are much larger than previously thought.

Scientists using the Kitt Peak National Observatory Mayall 4-meter telescope have categorized the home stars of many of those planet candidates. In particular, the researchers made detailed follow-up observations of 300 of the stars most likely to harbor exoplanets.

Astronomer Mark Everett led the study, which was presented Tuesday at the 222nd meeting of the American Astronomical Society, and will be published in an upcoming issue of the Astrophysical Journal.

Most of the stars we observed are slightly larger than previously thought and one quarter of them are at least 35 percent larger," Everett said. "Therefore, any planets orbiting these stars must be larger and hotter as well. By implication, these new results reduce the number of candidate Earth-size planet analogues detected by Kepler."

The stars observed by Everett and his team host more than 360 Kepler planet candidates, and the pool of Earth-like worlds may now be smaller.

"Determination of accurate stellar sizes allows astronomers to more accurately identify which exoplanets are Earth analogs, fulfilling a key goal of the Kepler mission," said Steve Howell, a Kepler project scientist who presented the group's findings.

Kepler has been suffering recently, and mission engineers are still trying to get the telescope back online. An essential reaction wheel failed after experiencing friction since January. Kepler has four such wheels to keep it precisely pointed in the right direction.

Kepler has "years of fuel," and if engineers can't correct the problem or fix the wheel, they may adapt the telescope to its new condition and scan the sky broadly rather than focus deeply in one direction.