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Many Planets Could Circle Twin Suns, NASA Says

Victoria Jaggard
National Geographic News
March 30, 2007
 
"But I was going into Toshi Station to pick up some power converters."

If life exists on other worlds, someone could be whining about doing their chores on a planet not unlike Star Wars's Tatooine.

The latest data from NASA's Spitzer Space Telescope suggests that the universe might be brimming with planets that have two suns like the desert world that Luke Skywalker called home (see related images from Spitzer).

More than half of all known star systems are binaries, with twin stars locked in a gravitational dance, NASA scientists say.

The new data show that dusty disks of debris that could be indicators of planet formation are just as abundant around binaries as they are around single stars.

"There could be countless planets out there with two or more suns," lead study author David Trilling of the University of Arizona, Tucson, said in a press release.

Trilling and colleagues will publish a paper on their research in the April 1 issue of the Astrophysical Journal.

Twin Suns

Existing techniques for looking directly for planets don't work very well when searching around binary stars.

Normally, planet hunters look for the so-called Doppler wobble as evidence of a planet's gravity tugging on its host star.

"But everything in a binary system is more complicated," Trilling told National Geographic News.

That's because, in addition to any planets in orbit, both stars are tugging on each other, he said. Each star's effect on the other would be great enough to mask the planet's effect.

So Trilling's team used Spitzer's infrared cameras to scan for planetary disks instead.

"Spitzer is very good at detecting emitted thermal radiation from dust," Trilling said. "When we're searching for the dust disks, we're looking at a wavelength at which the stars are faint but the dust is bright."

Of the 69 binary systems the team studied, 40 percent were shown to have these dusty disks, meaning they could very well have planets in orbit.

Tatooine Plausible

Astronomers had previously found that planetary disks exist in binary systems where the twin stars are very far apart from each other—about a hundred times farther apart than the distance between Earth and the sun.

Nearly 200 planets outside our solar system have been discovered so far with the wobble technique. About a quarter orbit one star in a binary system (related: "Many 'Earths' Are Out There, Study Says" [April 6, 2005]).

The latest project focused on binary stars that are much closer together—less than 500 times the distance between Earth and the sun.

What really astonished astronomers was that 60 percent of the tightly circling twin stars they saw had dusty disks—a setup that could create a scene like the Tatooine sunset in Star Wars.

This finding actually makes perfect sense, said Alan P. Boss, an expert in planet formation at the Carnegie Institution in Washington, D.C.

"The close binary appears to be pretty much a single, massive star to the material in orbit around it that is trying to form a planetary system," Boss said in an email interview.

And "if the planetary orbits are stable and at a distance where liquid water is possible, then they will be habitable."

If planets are in the dusty disks spied by Spitzer, there's no reason some of them couldn't support life, study author Trilling said.

"I've been thinking about it, and there's nothing astronomically wrong with that picture," he noted, referring to the famous movie still (see photo above).

"But it is still science fiction—there's no reason to believe it really exists."

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