NASA’s Kepler mission has discovered its first Earth-size planet candidates and its first candidates in the habitable zone, a region where liquid water could exist on a planet’s surface. Five of the potential planets are near Earth-size and orbit in the habitable zone of smaller, cooler stars than our Sun.
Candidates require follow-up observations to verify they are actual planets. Kepler also found six confirmed planets orbiting a Sun-like star, Kepler-11. This is the largest group of transiting planets orbiting a single star yet discovered outside our solar system.
“In one generation we have gone from extraterrestrial planets being a mainstay of science fiction, to the present, where Kepler has helped turn science fiction into today’s reality,” said NASA Administrator Charles Bolden. “These discoveries underscore the importance of NASA’s science missions, which consistently increase understanding of our place in the cosmos.”
The discoveries are part of several hundred new planet candidates identified in new Kepler mission science data, released Feb. 1. The findings increase the number of planet candidates identified by Kepler to-date to 1,235. Of these, 68 are approximately Earth-size; 288 are super-Earth-size; 662 are Neptune-size; 165 are the size of Jupiter and 19 are larger than Jupiter.
Of the 54 new planet candidates found in the habitable zone, five are near Earth-sized. The remaining 49 habitable zone candidates range from super-Earth size — up to twice the size of Earth—to larger than Jupiter.
The findings are based on the results of observations conducted May 12 to Sept. 17, 2009, of more than 156,000 stars in the Kepler telescope’s field of view, which covers approximately 1/400 of the sky.
“The fact that we’ve found so many planet candidates in such a tiny fraction of the sky suggests there are countless planets orbiting Sun-like stars in our galaxy,” said William Borucki of NASA’s Ames Research Center in Moffett Field, Calif., the mission’s science principal investigator. “We went from zero to 68 Earth-sized planet candidates and zero to 54 candidates in the habitable zone, some of which could have moons with liquid water.”
Among the stars with planetary candidates, 170 show evidence of multiple planetary candidates. Kepler-11, located approximately 2,000 light years from Earth, is the most tightly packed planetary system yet discovered. The Kepler-11 findings were published in the Feb. 3 issue of the journal Nature.
Kepler, a space telescope, looks for planet signatures by measuring tiny decreases in the brightness of stars caused by planets crossing in front of them. This is known as a transit.
Since transits of planets in the habitable zone of Sun-like stars occur about once a year and require three transits for verification, it is expected to take three years to locate and verify Earth-size planets orbiting Sun-like stars.
The Kepler science team uses ground-based telescopes and the Spitzer Space Telescope to review observations on planetary candidates and other objects of interest the spacecraft finds. The star field that Kepler observes in the constellations Cygnus and Lyra can only be seen from ground-based observatories in spring through early fall. The data from these other observations help determine which candidates can be validated as planets.
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