Spiral arms of dust and gas seen around two distant stars might be showing evidence of giant planets, 10 times as big as Jupiter, orbiting those stars, astronomers say.

The pancake shaped collections of dust and gas, known as circumstellar disks, are seen for a few million years after the stars form, they say.

Some scientists believe that new planets forming around those stars could betray their presence by causing changes in the shape or configuration of the circumstellar disks.

Astronomers focused on two distant young stars, SAO 206462 and MWC 758, both of which have surrounding disks that have been pulled or stretched into distinctive spiral shapes.

That may be the result of the gravity of giant planets interacting with the disk to increase its density in certain regions, the researchers suggest.

"Although it had been speculated that planets can produce spiral arms, we now think we know how," says researcher Zhaohuan Zhu of Princeton University.

The finding, reported in The Astrophysical Journal Letters, is useful because the planets often cannot be observed directly, he explains.

"Simulations also suggest that these spiral arms have rich information about the unseen planet, revealing not only its position but also its mass," he says.

If planets were not present, the disks would not display the spiral shapes seen, the researchers say.

The large scale of the spiral features in the disks around the two stars suggests the planets would have a mass at least 10 times that of Jupiter in our solar system, they add.

The discovery adds yet another weapon to the arsenal of astronomers searching the universe for exoplanets around distant stars, says study leader Ruobing Dong of the Lawrence Berkeley National Laboratory in California.

"It's difficult to see suspected planets inside a bright disk surrounding a young star," he says. "Based on this study, we are convinced that planets can gravitationally excite structures in the disk."

Such gravitationally induced features in a circumstellar disk could be "a smoking gun of forming planets," he says.

Other experts say they agree the new discovery can provide unique insights into how and when planets form.

"You can't learn a lot about how planets form by observing our solar system," says Tony Darnell, a spokesman for the Space Telescope Science Institute. "But you can by looking at these kinds of systems."