Kepler Discovers Earth-size Exoplanets   
       
   Dec 20, 2011:  NASA's Kepler mission has discovered the first Earth-size   
   planets orbiting a sun-like star outside our solar system. The planets, called   
   Kepler-20e and Kepler-20f, are too close to their star to be in the so-called   
   habitable zone where liquid water could exist on a planet's surface, but they   
   are the smallest exoplanets ever confirmed around a star like our sun.   
       
   The discovery marks the next important milestone in the ultimate search for   
   planets like Earth. The new planets are thought to be rocky. Kepler-20e is   
   slightly smaller than Venus, measuring 0.87 times the radius of Earth.   
   Kepler-20f is a bit larger than Earth, measuring 1.03 times its radius. Both   
   planets reside in a five-planet system called Kepler-20, approximately 1,000   
   light-years away in the constellation Lyra.   
       
   http://www.nasa.gov/mission_pages/kepler/multimedia/images/kepler-20-planet-l   
   ineup.html   
       
   This chart compares artist's concept images of the first Earth-size planets   
   found around a sun-like star to planets in our own solar system, Earth and   
   Venus. Image credit: NASA/Ames/JPL-Caltech   
      
   Kepler-20e orbits its parent star every 6.1 days and Kepler-20f every 19.6   
   days. These short orbital periods mean very hot, inhospitable worlds.   
   Kepler-20f, at 800 degrees Fahrenheit, is similar to an average day on the   
   planet Mercury. The surface temperature of Kepler-20e, at more than 1,400   
   degrees Fahrenheit, would melt glass.   
       
   "The primary goal of the Kepler mission is to find Earth-sized planets in the   
   habitable zone," said Francois Fressin of the Harvard-Smithsonian Center for   
   Astrophysics in Cambridge, Mass., lead author of a new study published in the   
   journal Nature. "This discovery demonstrates for the first time that   
   Earth-size planets exist around other stars, and that we are able to detect   
   them."   
       
   The Kepler-20 system includes three other planets that are larger than Earth   
   but smaller than Neptune. Kepler-20b, the closest planet, Kepler-20c, the   
   third planet, and Kepler-20d, the fifth planet, orbit their star every 3.7,   
   10.9 and 77.6 days. All five planets have orbits lying roughly within   
   Mercury's orbit in our solar system. The host star belongs to the same G-type   
   class as our sun, although it is slightly smaller and cooler.   
       
   The system has an unexpected arrangement. In our solar system, small, rocky   
   worlds orbit close to the sun and large, gaseous worlds orbit farther out. In   
   comparison, the planets of Kepler-20 are organized in alternating size: large,   
   small, large, small and large.   
       
   "The Kepler data are showing us some planetary systems have arrangements of   
   planets very different from that seen in our solar system," said Jack   
   Lissauer, planetary scientist and Kepler science team member at NASA's Ames   
   Research Center in Moffett Field, Calif. "The analysis of Kepler data continue   
   to reveal new insights about the diversity of planets and planetary systems   
   within our galaxy."   
       
   Scientists are not certain how the system evolved but they do not think the   
   planets formed in their existing locations. They theorize the planets formed   
   farther from their star and then migrated inward, likely through interactions   
   with the disk of material from which they originated. This allowed the worlds   
   to maintain their regular spacing despite alternating sizes.   
       
   The Kepler space telescope detects planets and planet candidates by measuring   
   dips in the brightness of more than 150,000 stars to search for planets   
   crossing in front, or transiting, their stars. The Kepler science team   
   requires at least three transits to verify a signal as a planet.   
       
   On Dec. 5 the team announced the discovery of Kepler-22b in the habitable zone   
   of its parent star. It is likely to be too large to have a rocky surface.   
   While Kepler-20e and Kepler-20f are Earth-size, they are too close to their   
   parent star to have liquid water on the surface.   
       
   "In the cosmic game of hide and seek, finding planets with just the right size   
   and just the right temperature seems only a matter of time," said Natalie   
   Batalha, Kepler deputy science team lead and professor of astronomy and   
   physics at San Jose State University. "We are on the edge of our seats knowing   
   that Kepler's most anticipated discoveries are still to come."   
       
   For more information about the Kepler mission and to view the digital press   
   kit, visit: http://www.nasa.gov/kepler   
       
       
   Production Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   NASA's Kepler Mission   
       
   Credits:  NASA's Ames Research Center manages Kepler's ground system   
   development, mission operations and science data analysis. NASA's Jet   
   Propulsion Laboratory in Pasadena, Calif., managed Kepler mission development.   
   Ball Aerospace and Technologies Corp. in Boulder, Colo., developed the Kepler   
   flight system and supports mission operations with the Laboratory for   
   Atmospheric and Space Physics at the University of Colorado in Boulder. The   
   Space Telescope Science Institute in Baltimore archives, hosts and distributes   
   the Kepler science data. Kepler is NASA's 10th Discovery Mission and is funded   
   by NASA's Science Mission Directorate at the agency's headquarters.   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.64   
    * Origin: NCS BBS (1:3828/7)