Planets with double suns are common

January 11, 2012

Astronomers using NASA's Kepler mission have discovered two new circumbinary planet systems - planets that orbit two stars, like Tatooine in the movie Star Wars. Their find, which brings the number of known circumbinary planets to three, shows that planets with two suns must be common, with many millions existing in our Galaxy.

"Once again, we're seeing science fact catching up with science fiction," said co-author Josh Carter of the Harvard-Smithsonian Center for Astrophysics.

The work was published online in the journal Nature and presented by lead author William Welsh (San Diego State University) at a press conference at a meeting of the American Astronomical Society.

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 themselves orbit each other every 28 days. Kepler-35b revolves around a pair of smaller stars (80 and 89 percent of the Sun's mass) every 131 days, and the stars orbit one another every 21 days. Both systems reside in the constellation Cygnus the Swan, with Kepler-34 located 4,900 light-years from Earth and Kepler-35 at a distance of 5,400 light-years.

Circumbinary planets have two suns, not just one, and due to the orbital motion of the stars, the amount of energy the planet receives varies greatly. This changing energy flow could produce wildly varying climates.

"It would be like cycling through all four seasons many times per year, with huge temperature changes," explained Welsh. "The effects of these climate swings on the atmospheric dynamics, and ultimately on the evolution of life on habitable circumbinary planets, is a fascinating topic that we are just beginning to explore."

The Kepler team announced the first circumbinary planet, Kepler-16b, last September. Like Kepler-16b, these new planets also transit (eclipse) their host stars, which is how Kepler spotted them. When only Kepler-16b was known, many questions remained about the nature of circumbinary planets; most importantly, was it a fluke? With the discovery of these two new worlds, astronomers can now answer many of those questions as they begin to study an entirely new class of planets.

"It was once believed that the environment around a pair of stars would be too chaotic for a circumbinary planet to form, but now that we have confirmed three such planets, we know that it is possible, if not probable, that there are at least millions in the Galaxy," said Welsh.

"The search is on for more circumbinary planets," agreed Carter, "and we hope to use Kepler for years to come."
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Harvard-Smithsonian Center for Astrophysics

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