Kepler Discovers a Planet with Two Suns   
       
   Sept. 15, 2011: The existence of a world with a double sunset, as portrayed in   
   the film Star Wars more than 30 years ago, is now scientific fact. NASA's   
   Kepler mission has made the first unambiguous detection of a circumbinary   
   planet -- a planet orbiting two stars -- 200 light-years from Earth.   
       
   Unlike Star Wars' Tatooine, the planet is cold, gaseous and not thought to   
   harbor life, but its discovery demonstrates the diversity of planets in our   
   galaxy. Previous research has hinted at the existence of circumbinary planets,   
   but clear confirmation proved elusive. Kepler detected such a planet, known as   
   Kepler-16b, by observing transits, where the brightness of a parent star dims   
   from the planet crossing in front of it.   
       
   "This discovery confirms a new class of planetary systems that could harbor   
   life," Kepler principal investigator William Borucki said. "Given that most   
   stars in our galaxy are part of a binary system, this means the opportunities   
   for life are much broader than if planets form only around single stars. This   
   milestone discovery confirms a theory that scientists have had for decades but   
   could not prove until now."   
       
   http://www.nasa.gov/mission_pages/kepler/multimedia/images/Kepler-16_planet-p   
   ov-art.html   
       
   An artist's concept of Kepler-16b, the first planet known to definitively   
   orbit two stars -- what's called a circumbinary planet. The planet, which can   
   be seen in the foreground, was discovered by NASA's Kepler mission.   
   A research team led by Laurance Doyle of the SETI Institute in Mountain View,   
   Calif., used data from the Kepler space telescope, which measures dips in the   
   brightness of more than 150,000 stars, to search for transiting planets.   
   Kepler is the first NASA mission capable of finding Earth-size planets in or   
   near the "habitable zone," the region in a planetary system where liquid water   
   can exist on the surface of the orbiting planet.   
       
   Scientists detected the new planet in the Kepler-16 system, a pair of orbiting   
   stars that eclipse each other from our vantage point on Earth. When the   
   smaller star partially blocks the larger star, a primary eclipse occurs, and a   
   secondary eclipse occurs when the smaller star is occulted, or completely   
   blocked, by the larger star.   
       
   Astronomers further observed that the brightness of the system dipped even   
   when the stars were not eclipsing one another, hinting at a third body. The   
   additional dimming in brightness events, called the tertiary and quaternary   
   eclipses, reappeared at irregular intervals of time, indicating the stars were   
   in different positions in their orbit each time the third body passed. This   
   showed the third body was circling, not just one, but both stars, in a wide   
   circumbinary orbit.   
       
   The gravitational tug on the stars, measured by changes in their eclipse   
   times, was a good indicator of the mass of the third body. Only a very slight   
   gravitational pull was detected, one that only could be caused by a small   
   mass. The findings are described in a new study published Friday, Sept. 16, in   
   the journal Science.   
       
   "Most of what we know about the sizes of stars comes from such eclipsing   
   binary systems, and most of what we know about the size of planets comes from   
   transits," said Doyle, who also is the lead author and a Kepler participating   
   scientist. "Kepler-16 combines the best of both worlds, with stellar eclipses   
   and planetary transits in one system."   
       
   This discovery confirms that Kepler-16b is an inhospitable, cold world about   
   the size of Saturn and thought to be made up of about half rock and half gas.   
   The parent stars are smaller than our sun. One is 69 percent the mass of the   
   sun and the other only 20 percent. Kepler-16b orbits around both stars every   
   229 days, similar to Venus' 225-day orbit, but lies outside the system's   
   habitable zone, where liquid water could exist on the surface, because the   
   stars are cooler than our sun.   
       
   "Working in film, we often are tasked with creating something never before   
   seen," said visual effects supervisor John Knoll of Industrial Light & Magic,   
   a division of Lucasfilm Ltd., in San Francisco. "However, more often than not,   
   scientific discoveries prove to be more spectacular than anything we dare   
   imagine. There is no doubt these discoveries influence and inspire   
   storytellers. Their very existence serves as cause to dream bigger and open   
   our minds to new possibilities beyond what we think we 'know.'"   
       
   For more information about the Kepler-16 discovery, visit:   
       
   http://kepler.nasa.gov/Mission/discoveries/kepler16b/   
       
       
   Production Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   more images and animations   
       
   Kepler home page -- from nasa.gov   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.64   
    * Origin: NCS BBS (1:3828/7)