Kepler Discovers Smallest 'Habitable Zone' Planets

NASA's Kepler mission has discovered two new planetary systems that include three super-Earth-size planets in the "habitable zone," the range of distance from a star where the surface temperature of an orbiting planet might be suitable for liquid water.

The two planetary systems are Kepler-62 and Kepler-69.  The Kepler-62 system has five planets; 62b, 62c, 62d, 62e and 62f. The Kepler-69 system has two planets; 69b and 69c. Kepler-62e, 62f and 69c are the habitable-zone "super Earths."

"The discovery of these rocky planets in the habitable zone brings us a bit closer to finding a place like home," said John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters. "It is only a matter of time before we know if the galaxy is home to a multitude of planets like Earth, or if we are a rarity."

The  planets of the Kepler-62 system orbit a star classified as a K2 dwarf, measuring just two-thirds the size of the sun and only one-fifth as bright. At seven billion years old, the star is somewhat older than the sun. It is about 1,200 light-years from Earth in the constellation Lyra.

Kepler-62f is only 40 percent larger than Earth, making it the exoplanet closest to the size of our planet known in the habitable zone of another star. Kepler-62f is likely to have a rocky composition. Kepler-62e, orbits on the inner edge of the habitable zone and is roughly 60 percent larger than Earth.

The planets of the Kepler-69 orbit a star in the same class as our sun, called G-type. It is 93 percent the size of the sun and 80 percent as luminous and is located approximately 2,700 light-years from Earth in the constellation Cygnus.

Kepler-69c is 70 percent larger than the size of Earth. Astronomers are uncertain about the composition of Kepler-69c, but its orbit of 242 days around a sun-like star resembles that of our neighboring planet Venus.

"We only know of one star that hosts a planet with life, the sun. Finding a planet in the habitable zone around a star like our sun is a significant milestone toward finding truly Earth-like planets," said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute, and lead author of the Kepler-69 system discovery published in the Astrophysical Journal.

"Kepler has brought a resurgence of astronomical discoveries and we are making excellent progress toward determining if planets like ours are the exception or the rule," added William Borucki, Kepler science principal investigator at NASA's Ames and lead author of the Kepler-62 system paper in Science.

Scientists do not know whether life could exist on the newfound planets, but their discovery signals we are another step closer to finding a world similar to Earth around a star like our sun.

Says Grunsfeld, "the Kepler spacecraft has certainly turned out to be a rock star of science."

For more information about the Kepler mission and to view the digital press kit, visithttp://www.nasa.gov/kepler