Hubble Space Telescope's picture of Fomalhaut debris ring (click for larger image)

It took about seven years, but NASA has finally found a planet that circles another star.

The Hubble Space Telescope took the first visible-light snapshot of Fomalhaut b, which orbits a southern star, called Fomalhaut, about 25 light-years away.

NASA said Thursday that the planet is estimated to be less than three times Jupiter's mass, and the star is part of the constellation Piscis Australis, or the "Southern Fish." The finding has been published in the Nov. 14 issue of Science magazine.

In the early 1980s, NASA's Infrared Astronomy Satellite discovered dust around the star. In 2004, a high-resolution camera on Hubble's Advanced Camera for Surveys produced the first resolved visible-light image of the region and found a ring of protoplanetary debris, about 21.5 billion miles across. It had a sharp inner edge, indicating that a planet had a gravitational effect on the ring particles. The ring resembles the Kuiper Belt around the solar system. That belt consists of objects that range in size from dust particles to dwarf planets, like Pluto.

In 2005, Hubble astronomer Paul Kalas, of the University of California at Berkeley, and others hypothesized that a planet between the star, Fomalhaut, and the inner edge of the ring had a gravitational effect that offset the ring from the center of the star. Independent researchers supported the theory.

Now, Hubble has captured evidence. It photographed a point source of light 1.8 billion miles inside the ring's inner edge, NASA said.

NASA said that Hubble's Advanced Camera for Surveys' coronagraph showed in observations taken 21 months apart that the object moves around the star, indicating it is gravitationally tied to it. The planet is 10.7 billion miles from the star.

Scientists believe that the planet may have a Saturn-like ring of ice and dust that reflects starlight, since it's brighter than expected for its size.

"Our Hubble observations were incredibly demanding," Kalas said. "Fomalhaut b is 1 billion times fainter than the star. We began this program in 2001, and our persistence finally paid off."

NASA hopes that its James Webb Space Telescope, scheduled for launch in 2013, will capture infrared images while searching for other planets and asteroid belts. NASA also will seek signs of water vapor clouds and give a glimpse of how the 100 million-year-old planet evolved.

"Fomalhaut is the gift that keeps on giving," team member Mark Clampin of NASA's Goddard Space Flight Center in Greenbelt, Md., said in a statement. "Following the unexpected discovery of its dust ring, we have now found an exoplanet at a location suggested by analysis of the dust ring's shape. The lesson for exoplanet hunters is 'follow the dust.'"