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Planet hunters find Tatooine-like system

tattooine.jpg NASA’s planet-hunting telescope has spotted one of the touchstones of science fiction: a circumbinary, or a planet that orbits two stars.

The discovery, announced today in the journal Science, comes from the Kepler mission, which has been staring at 155,000 stars in the same patch of sky since its 2009 launch, looking for the slight dimming of light that occurs when a planet passes in front of its parent star.

In this circumbinary system, however, Kepler detected four such dimmings: two that occur when the stars eclipse each other, and then two much smaller ones when the planet, about the size of Saturn, crosses in front of each star. The stars are about 20% and 69% as massive as the Sun, respectively, and orbit each other every 41 days. The planet has a nearly circular 229-day orbit.

A few other examples of circumbinaries had been found before by looking for slight irregularities in the timing of the binary star eclipses — an indication that the tiny gravitational tug of a planet might be upsetting the pas de deux of the binaries. But the evidence from Kepler, with its transit observations, is far more direct. At a NASA press conference this afternoon, a representative from Lucasfilm’s Industrial Light and Magic was included to comment on the similarities between the planet, Kepler 16b, and Tatooine, the imagined planetary home for Luke Skywalker in Star Wars.

What’s remarkable is that astronomers caught the circumbinary at all. The planet’s orbit is within 0.4 degrees of the plane in which the two stars orbit each other. Even that slight amount of tilt means that the transits can be viewed from Earth only 40% of the time; one of the transits is expected to stop occurring beginning in May 2014.

But the high amount of co-planarity between the planet and its stars indicates that the planet, rather than being captured, formed from the same disk of dust and gas as the two stars — a novel situation that presents some challenges for solar system formation models. It also indicates that planets might not be quite so hard to achieve in binary systems, which comprise roughly half of the star systems in the sky.

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    Derek Silva said:

    Now let’s go out there and find an Arrakis-like planet and solar system. Then we can start harvesting melange!

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