The scientists say the data shows that about half the planets in the galaxy either have no surface or an extremely inhospitable atmosphere that is not likely to be compatible with life. All of Kepler's observations were in a small patch of sky between the constellations of Cygnus and Lyra.
Kepler has already discovered 4,034 potential exoplanets, 2,335 of which have been confirmed by other telescopes as actual planets.
The Kepler telescope detects the presence of planets by registering minuscule drops in a star's brightness that occurs when a planet crosses in front of it, a movement known as a transit. "Both results have significant implications for the search for life", NASA reports. The mission has also found 50 candidates similar in size to Earth, with more than 30 of them confirmed.
And it only looked in a tiny part of the galaxy, one quarter of one percent of a galaxy that holds about 200 billion of stars. "Understanding their frequency in the galaxy will help inform the design of future NASA missions to directly image another Earth". Kepler's main mission ended in 2013 after the failure of two of its four wheels that control its orientation in space.
One of Kepler's other big surprises was a profusion of planets intermediate in size between Earth and Neptune.
As a sort of insurance policy to ensure there was no under or over counting of planets, the scientists running the mission introduced simulations of transits by planets into the Kepler data set to figure out whether Kepler was mis-identifying planets. Then, they added data that appear to come from a planet, but were actually false signals, and checked how often the analysis mistook these for planet candidates. "It's unbelievable the things that Kepler has found, it has shown us these terrestrial worlds, and we still have all this work to do to understand how common Earths are in the galaxy".
One research group took advantage of the Kepler data to make precise measurements of thousands of planets, revealing two distinct groups of small planets.
After four years of searching, the Kepler telescope has detected a total of 49 planets in the Goldilocks zone. He likened the discovery to realizing that mammals and reptiles are on separate branches of the evolutionary tree.
These planets are usually 1.6 times the size of Earth, with rocky terrain.
The U.S. space agency says that these 10 new candidates are in the correct range of their stars where water could form on the surface of the more rocky planets. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development.
Ames manages the Kepler missions for NASA's Science Mission Directorate.
Jet Propulsion Laboratory, Pasadena, Calif.