Thursday, January 19, 2012

A Planet with Two Suns

Star Wars' planets with two suns are common, says Nasa - and could be a hunting ground for alien life
 Tatooine, the desert planet with two suns where Luke Skywalker grows up, is one of the Star Wars series' best-loved settings. Nasa's Kepler telescope detected two new planet systems with two suns - named Kepler-34 and Kepler-35 - leading Nasa astronomers to say that planets like the fictional Tatooine are common.
Many could be a good hunting ground for planets that support life, says William Welsh of San Diego University.

'This discovery broadens the hunting ground for systems that could support life.'The two new planets, named Kepler-34b and Kepler-35b, are both gaseous Saturn-size planets. Kepler-34b orbits its two sun-like stars every 289 days, and the stars orbit one another every 28 days. The planets reside too close to their parent stars to be in the 'habitable zone' - the region where liquid water could exist on a planet's surface.At 4,900 and 5,400 light-years from Earth, located in the constellation Cygnus, Kepler-34b and Kepler-35b are among the most distant planets discovered. 'This work further establishes that such 'two sun' planets are not rare exceptions, but may in fact be common, with many millions existing in our galaxy,' said William Welsh of San Diego State University, who led the study. The findings are described in a new study published Wednesday, Jan. 11, 2012 in the journal Nature.

Before this, 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.

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