Three super-Earth-sized planets in two newly discovered planetary systems are in a “habitable zone” – a distance from their stars suitable for supporting liquid water – and could potentially support life as we know it, according to NASA’s Kepler mission. “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 in Washington. “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 Kepler space telescope, which simultaneously and continuously measures the brightness of more than 150,000 stars, is NASA’s tenth Discovery Mission and the first mission capable of detecting Earth-sized planets around stars like our sun. It has found five planets in the Kepler-62 system: 62b, 62c, 62d, 62e and 62f; and two planets in the Kepler-69 system: 69b and 69c. Kepler-62e, 62f and 69c are the super-Earth-sized planets. Relative sizes of Kepler habitable-zone planets discovered as of April 18, 2013. From left: Kepler-22b, Kepler-69c, Kepler-62e, Kepler-62f and Earth (except for Earth, these are artists’ renditions). It is not yet known whether life could exist on the newfound planets, but the discovery signals that we are another step closer to finding a world similar to Earth around a star like our sun. “We only know of one star that hosts a planet with life: the sun,” said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, Calif., and lead author of the Kepler-69 system discovery published in The Astrophysical Journal. “Finding a planet in the habitable zone around a star like our sun is a significant milestone toward finding truly Earthlike planets.” The five 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 7 billion years old, the star is somewhat older than the sun. It is about 1200 light-years from Earth and in the constellation Lyra. The diagram compares the planets of the inner solar system to Kepler-62, a five-planet system about 1200 light-years from Earth in the constellation Lyra. The five planets of Kepler-62 orbit a star classified as a K2 dwarf, measuring just two-thirds the size of the sun and only one-fifth as bright. At 7 billion years old, the star is somewhat older than the sun. The artistic concepts of the Kepler-62 planets are the result of scientists and artists collaborating to help imagine the appearance of these distant worlds. When a planet candidate transits, or passes in front of the star from the spacecraft’s vantage point, a percentage of light from the star is blocked. The resulting dip in the brightness of the starlight reveals the transiting planet’s size relative to its star. Using the transit method, Kepler has detected 2740 candidates. Using various analysis techniques, ground telescopes and other space assets, 122 planets have been confirmed. Early in the mission, the Kepler telescope found primarily large, gaseous giants in very close orbits of their stars. The size and very short orbital period of these “hot Jupiters,” as they are known, make them easy to detect. Earth would take three years to accomplish the three transits required to be accepted as a planet candidate. As Kepler’s data continues to be analyzed, transit signals of habitable-zone planets the size of Earth orbiting stars like the sun will begin to emerge. “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,” said William Borucki, Kepler science principal investigator at NASA’s Ames Research Center at Moffett Field, Calif., and lead author of the paper appearing in Science (doi: 10.1126/science.1234702).