The double sunset that Luke Skywalker gazed upon in the film Star Wars might not be a fantasy. Astronomers using NASA's Spitzer Space Telescope have observed that planetary systems -- dusty disks of asteroids, comets and possibly planets -- are at least as abundant in twin-star systems as they are in single-star systems like our own. Since more than half of all stars are twins, or binaries, the finding suggests the universe is packed with planets that have two suns. Sunsets on some of those worlds would resemble the ones on Tatooine where two fiery balls dip below the horizon one by one.

"There appears to be no bias against having planetary system formation in binary systems," said David Trilling of the University of Arizona, Tucson, lead author of a new paper about the research appearing in the April 1 issue of the Astrophysical Journal. "There could be countless planets out there with two or more suns."

Previously, astronomers knew that planets could form in exceptionally wide binary systems, in which stars are 1,000 times farther apart than the distance between Earth and the sun, or 1,000 astronomical units. Of the approximately 200 planets discovered so far outside our solar system, about 50 orbit one member of a wide stellar duo.

"Binary systems were largely ignored before," added Trilling. "They are more difficult to study, but they might be the most common sites for planet formation in our galaxy."

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