Planet (or Is It?) Found Orbiting Star

German astronomers have published a photograph of an object 450 light-years from Earth that they say could be the first taken of a planet outside our solar system.

The finding has spurred debate over whether the object qualifies as a planet -- and claims from competing astronomers that they already produced an image of a different possible planet a year ago.

At issue is the mass of the object, which circles a million-year-old star named GQ Lup. If the new object’s mass is greater than 13 times that of Jupiter, it would be considered a brown dwarf -- a failed star -- and not a planet.

The astronomers estimated the object’s mass by measuring its brightness, a technique based on models that are still poorly developed.

“I am pretty sure that it’s a planet,” said the lead author, Richard Neuhaeuser, director of the Astrophysics Institute and University Observatory in Jena, Germany.

The best estimates, he said, place the object’s mass at twice that of Jupiter’s. Other models, he said, resulted in a figure of up to 42 Jupiter masses.

The paper, released online by the journal Astrophysics & Astronomy, stopped short of calling the object a planet, opting for “companion.”

About 150 planets have been discovered outside the solar system. Planets and the stars they orbit exert gravitational force on each other, making it possible to detect planets -- without actually seeing them -- by looking for wobbly stars. The planets are difficult to photograph because they give off little light.

The object the German astronomers found is young in astronomical terms and still emitting light as it cools.

The published image was taken June 25, 2004, by the European Southern Observatory’s Very Large Telescope in Chile. Other images, dating to 1999, were used to confirm that the body is orbiting a star. It takes 1,200 Earth years to complete one revolution around its star, which is part of the Lupus constellation.

Last year, a French-led group announced that it had photographed another potential planet, an object 225 light-years away that appears to be orbiting the brown dwarf known as 2M1207 in the constellation Hydra.

Ben Zuckerman, a professor of physics and astronomy at UCLA who was part of that team, said the group had as much claim as the Germans to being the first to photograph a planet outside our solar system.

The object they found is roughly 8 million years old, an age that he and other astronomers said allowed for a more reliable measure of its mass. It was estimated to be five times the mass of Jupiter.

But doubt remains about whether that object was orbiting a star -- a key requirement for planet status -- or was a body lurking in the stellar background.

To complicate matters, the star in question is a brown dwarf.

Could the object in the French image still be considered a planet?

Alan Boss, an astrophysicist at the Carnegie Institution of Washington, said he recently put the question before members of the International Astronomical Union’s working group on extrasolar planets.

“Half said they thought it was a planet,” he said. “Half said they thought it wasn’t a planet.”