U.S. astronomers say some of the hundreds of planets that once orbited stars outside our solar system may have fallen into their stars and no longer exist.

University of Washington astronomer Rory Barnes says recent computer modeling has provided the first evidence gravitational forces might pull a planet into its parent star.

"When we look at the observed properties of extrasolar planets, we can see that this has already happened -- some extrasolar planets have already fallen into their stars," he said.

Computer models can show where planets should line up in a particular star system, but direct observations show some systems are missing planets close to the stars where models say they should be.

The researchers said they hope their findings lead to a better understanding of how stars destroy planets and how that process might affect a planet's orbit, Jackson said.

Barnes is co-author of a paper with Brian Jackson and Richard Greenberg of the Lunar and Planetary Laboratory at the University of Arizona. The paper has been accepted for publication in the Astrophysical Journal.