The space agency said today its Kepler space telescope spotted what it called its first Earth-size planet candidates and its first candidates in what it considers to be the habitable zone, a region where liquid water could exist on a planet's surface. 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.
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The discoveries are part of several hundred new planet candidates identified by Kepler mission science data this week. The discoveries 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, NASA stated.
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, NASA stated.
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. All six of its confirmed planets have orbits smaller than Venus, and five of the six have orbits smaller than Mercury's. The only other star with more than one confirmed transiting planet is Kepler-9, which has three, NASA stated.
"Kepler-11 is a remarkable system whose architecture and dynamics provide clues about its formation," said Jack Lissauer, a planetary scientist and Kepler science team member at NASA Ames in a statement. "These six planets are mixtures of rock and gases, possibly including water. The rocky material accounts for most of the planets' mass, while the gas takes up most of their volume. By measuring the sizes and masses of the five inner planets, we determined they are among the lowest mass confirmed planets beyond our solar system."
Kepler has been busy. In January Kepler spotted its first rocky planet orbiting a sun similar to our own -- 560 light years from our solar system. While not in an area of space considered habitable, the rocky planet known as Kepler-10b and is never-the-less significant because it showcases the ability of Kepler to find and track such small exoplanetary movements.
According to NASA: "Kepler's ultra-precise photometer measures the tiny decrease in a star's brightness that occurs when a planet crosses in front of it. The size of the planet can be derived from periodic dips in brightness. The distance between the planet and the star is calculated by measuring the time between successive dips as the planet orbits the star, NASA stated."
Kepler has already made a number of other key space discoveries.
In August, Kepler discovered two Saturn-sized exoplanets crossing in front of, or transiting, the same star. At the time NASA said in addition to the two confirmed giant planets, Kepler spotted what appears to be a third, much smaller transit signature in the observations of the sun-like star designated Kepler-9, which is 2,000 light years away from Earth. The planets were named Kepler-9b and 9c.
NASA reported last January Kepler spotted five planets orbiting stars beyond our own solar system. The five planets are called "hot Jupiters" because of their deep mass and extreme temperatures, NASA said. They range in size from about the same size as Neptune to larger than Jupiter and have orbits ranging from 3.3 to 4.9 days, NASA stated. The orbs likely have no known living organisms because NASA estimates their temperatures to range from 2,200 to 3,000 degrees Fahrenheit, hotter than molten lava and all five orbit stars hotter and larger than Earth's sun. In June, mission scientists announced the mission has identified more than 700 planet candidates that it had not confirmed as planets.
The grand prize for Kepler of course would be finding a planet similar to Earth or those that orbit stars in a warm habitable zone where liquid water could exist on the surface of the planet, according to NASA. Since transits of planets in the habitable zone of solar-like stars occur about once a year and require three transits for verification, it is expected to take at least three years to locate and verify an Earth-size planet, NASA stated. The satellite has been peering at a patch of space, scanning over 150,000 stars since 2009.
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