NASA's Kepler spacecraft has discovered a distant planetary system, in which planets do not circle a single star, but rather orbit two stars. This rare type of planetary systems is termed circumbinary system, since the central object is a binary star, two gravitationally-bound stars orbiting each other. The newly discovered system, known as Kepler-47, is located 4,900 light-years away from Earth, and is visible in the sky among stars of the remarkable constellation Cygnus, The Swan.
This discovery demonstrates that several planets can form and persist in the stressful environment surrounding a binary star, and reveals the diversity of planetary systems in our Milky Way Galaxy.
Astronomers detected two planets in the Kepler-47 system. Interestingly, the system’s stars eclipse each other every 7.5 days. The larger of the two stars is similar to the Sun in size, but only 84 percent as bright. The smaller star is a dwarf, measuring only one-third the Sun’s size and less than 1 percent as bright.
The planets have been given the designations Kepler-47b and Kepler-47c. The inner planet, Kepler-47b, orbits the pair of stars in less than 50 days. Its diameter is three times larger than Earth’s, and it is thought to be a very hot world.
The outer planet, Kepler-47c, orbits its parent stars every 303 days, within the so-called "habitable zone," the region in a planetary system where liquid water might exist on the surface of a planet. Kepler-47c is thought to be a gaseous giant slightly larger than Neptune, the fourth largest planet. It might be enveloped by an atmosphere of thick bright water-vapor clouds.
"Unlike our Sun, many stars are part of multiple-star systems where two or more stars orbit one another. The question always has been -- do they have planets and planetary systems? This Kepler discovery proves that they do," said William Borucki, Kepler mission principal investigator. "In our search for habitable planets, we have found more opportunities for life to exist."
To search for planets beyond the Solar System, the Kepler spacecraft monitors the brightness of over 150,000 stars located within a small field of sky. When an unknown planet passes in front of one of these stars, Kepler measures a slight decrease in the star’s brightness, allowing astronomers to discover and track the planet. Kepler was launched in March 2009, and was placed into an orbit around the Sun.
References
NASA
www.nasa.gov/
Wikipedia