Kepler Finds 3 Smallest Planets Ever Detected Outside Solar System

Using data from NASA's Kepler mission, astronomers have discovered the three smallest planets yet detected orbiting a star beyond our sun, a news release from announced Wednesday.

The planets orbit a single star and are 0.78, 0.73 and 0.57 times the radius of Earth, with the smallest roughly about the size of Mars.

Like Earth, all three planets are thought to be rocky. However, they orbit close to their star, making them too hot to be in the habitable zone (regions where water could exist.) The press release pointed out that of the more than 700 planets confirmed to orbit other stars -- exoplanets -- only a handful are known to be rocky.

"Astronomers are just beginning to confirm the thousands of planet candidates uncovered by Kepler so far," Doug Hudgins, Kepler program scientist at NASA Headquarters in Washington, said in a prepared statement.

"Finding one as small as Mars is amazing, and hints that there may be a bounty of rocky planets all around us."

The Mission

Kepler continuously monitors more than 150,000 stars, looking for "telltale dips'' in their brightness. Follow-up observations from ground-based telescopes also are needed to confirm the discovery of planets.

The latest discovery comes from a team led by astronomers at the California Institute of Technology. The team used data publicly released by the Kepler mission, along with follow-up observations from the Palomar Observatory, near San Diego, and the W.M. Keck Observatory atop Mauna Kea in Hawaii. Their measurements dramatically revised the sizes of the planets from what was originally estimated, revealing their small nature, the release states.

For the latest Kepler discovery, the team obtained the sizes of the three planets (called KOI-961.01, KOI-961.02 and KOI-961.03) with the help of a well-studied twin star to KOI-961, Barnard's Star. A better understanding of the KOI-961 star, allowed the team to determine how big the planets must have to be to cause the dips in starlight.

NASA's Ames Research Center in Moffett Field, CA manages Kepler's ground system development, mission operations and science data analysis. JPL managed the Kepler mission's development.

For information about the Kepler mission, visit: http://www.nasa.gov/kepler .