Kepler Captures Planetary Group Orbiting Stellar Pair
Sharing the Light of Two Suns: This artist's concept illustrates Kepler-47, the first transiting circumbinary system. Credit: NASA/JPL-Caltech/T. Pyle
What’s new under the Sun? How about what’s new under two suns! NASA’s Kepler mission just released the news of multiple planets orbiting a binary star system.
This is the first time a circumbinary planetary system has been confirmed. Less than a year ago, a circumbinary planet, Kepler-16b was discovered. Now there is proof that more than one planet can form and survive the huge gravitational stress of a binary star.
Astronomers detected two planets in the Kepler-47 system, located approximately 4,900 light years from Earth in the constellation of Cygnus. This pair of orbiting stars that eclipse each other every 7.5 days, as seen from Earth, aren’t twins – they’re disparate. The larger star is much like the Sun, about the same mass but only 84% as bright. Its companion is much smaller – only about one-third the size of Sol and less than 1% as luminous.
“In contrast to a single planet orbiting a single star, the planet in a circumbinary system must transit a ‘moving target.’ As a consequence, time intervals between the transits and their durations can vary substantially, sometimes short, other times long,” said Jerome Orosz, associate professor of astronomy at San Diego State University and lead author of the paper. “The intervals were the telltale sign these planets are in circumbinary orbits.”
The inner planet, Kepler-47b, orbits the pair of stars in less than 50 days and can only be “seen” through the transit method. Astronomers speculate its a very hot world, one perhaps very similar to Venus – but roughly three times the radius of Earth. Known as Kepler-47b, it is the smallest known transiting circumbinary planet. Its outer companion, Kepler-47c, orbits the binary star system every 303 days. Oddly enough, it’s is located in the “habitable zone“. This means the distance conditions make it right to perhaps contain liquid water. While it wouldn’t be particularly conducive to life, it may closely match the conditions of planets like Neptune, where water-vapor might exist in the atmosphere.
“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 at NASA’s Ames Research Center in Moffett Field, Calif. “In our search for habitable planets, we have found more opportunities for life to exist.”
Imagine a world with two different Suns in the sky, similar to Luke Skywalker’s home desert planet Tatooine in “Star Wars.”
“While the outer planet is probably a gas giant planet and thus not suitable for life, large moons, if present, would be interesting worlds to investigate as they could potentially harbour life,” says William Welsh (San Diego State University, USA), co-author of the study.
Just what led to the discovery? In the search for transiting planets, the research team used data from the Kepler space telescope, which records changes in the brightness of more than 150,000 stars. Additional ground-based spectroscopic observations using telescopes at the McDonald Observatory at the University of Texas at Austin further refined the stellar properties. The findings are published in the journal Science.
“The presence of a full-fledged circumbinary planetary system orbiting Kepler-47 is an amazing discovery,” said Greg Laughlin, professor of Astrophysics and Planetary Science at the University of California in Santa Cruz. “These planets are very difficult to form using the currently accepted paradigm, and I believe that theorists, myself included, will be going back to the drawing board to try to improve our understanding of how planets are assembled in dusty circumbinary disks.”
“Since about one third of all stars are either binary or multiple star systems, finding planets in binary star systems has very important implications not only for estimating the total numbers of planets that exist, but for how star-planet systems form as well,” concludes Jerome Orosz.
Original Story Source: NASA Kepler Mission News.
