NASA’s Kepler mission has discovered the first two-planet solar system around a binary star, with the help of astronomers at the University of Texas at Austin utilizing two telescopes at the University’s McDonald’s observatory at West Texas. The discovery confirms that planetary systems can form around binary stars.
The binary star is Kepler-47. The main star is approximately the Sun’s mass. The accomplice is an M-dwarf star about one-third its size. The inner planet is thrice the Earth’s size and orbits around the binary star once in 49.5 days and the outer planet is 4.6 time the size of the Earth orbiting once every 303.2 days. The outer planet is the first planet found in a “habitable zone”, where water may be available. But the planet’s huge size (similar to Uranus) makes it an ice giant that may not support life forms. Analysis of the stars’ orbits demonstrated that daylight on the planets would differ largely over the 7.4 Earth-day duration as the stars finish their orbits and come closer to and move farther from the two planets, which are also moving.
The Kepler mission watched out for tiny dips in the quantity of light emanating from a star which might indicate that a planet is passing before it, which is called “transit”. Eclipsing of binary stars can be identified by telescopes wherein binary stars cross each other as they orbit. In case of Kepler-47 both planetary transits and stellar eclipses were seen in one system.
Astronomers at the MCDonald observatory studied the system through the Hobby-Eberly Telescope and the Harlan J. Smith Telescope. They looked for indications of movement of the main star through its light attributes and they calculated its mass. The secondary star was too indistinct to be gauged.