Twin-star systems enjoy double sunset.(Planets)

The double sunset that Luke Skywalker gazed upon in the film "Star Wars" might not be a fantasy, as astronomers using NASA's Spitzer Space Telescope have observed that certain celestial systems--containing dusty disks of asteroids, comets, and, possibly, planets--are at least as abundant in twin-star setups as they are in those, like our own, with only one star. 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 Skywalker's planet, 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," says David Trilling of the University of Arizona, Tucson, lead author of a paper about this research. "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.

The Spitzer study focuses on binary stars that are a bit more snug, with separation distances between zero and 500 astronomical units. Until now, not much was known about whether the close proximity of stars like these might affect the growth of planets. Standard ...