Photo marks milestone in planet search

By Robert Roy Britt

Senior science writer

updated 11:04 p.m. ET April 1, 2005

After a few close calls, astronomers have finally obtained the first photograph of a planet beyond our solar system, Space.com has learned.

And this time they say they're sure — alhough some doubt lingers about the mass of the object.

The planet is thought to be one to two times as massive as Jupiter, according to the scientists who imaged it. It orbits a star similar to a young version of our sun.

The star, GQ Lupi, has been observed by a team of European astronomers since 1999. They have made three images using the Very Large Telescope of the European Southern Observatory in Chile. The Hubble Space Telescope and the Japanese Subaru Telescope each contributed an image, too.

The work was led by Ralph Neuhaeuser of the Astrophysical Institute & University Observatory.

"The detection of the faint object near the bright star is certain," Neuhaeuser told Space.com on Friday.

The system is young, so the planet is rather warm, like a bun fresh out of the oven. That warmth made it comparatively easier to see in the glare of its host star compared with more mature planets. Also, the planet is very far from the star — about 100 times the distance between Earth and the sun, another factor in helping to separate the light between the two objects.

The discovery will be detailed in an upcoming issue of the journal Astronomy & Astrophysics. Neuhaeuser's co-authors include Ph.D. student Markus Mugrauer, who performed the observations, and Guenther Wuchterl.

The object appears to be "the first directly imaged and confirmed companion to a sunlike star, and as such [would mark] the dawn of a new era in planet detection," said Ray Jayawardhana, a University of Toronto researcher who was not involved in the discovery but has seen the scientific paper.

Jayawardhana added, though, that some models used to estimate the object's heft show it could be tens of times as massive as Jupiter, in which case it might cross over into the territory, bulk-wise, of a failed type of star known as a brown dwarf.

Other recent milestones
Over the past decade, astronomers have found about 150 extrasolar planets. The vast majority have only been detected indirectly, by noting wobbles that the planets induce in their stars.

Earlier this month, astronomers announced the detection of a planet's infrared light using the Spitzer Space Telescope. But that observation did not involve a photograph. Instead, the system's total light was seen to drop when the planet was eclipsed by the star.

Late last year, another European team announced what might have been the first photograph of an extrasolar planet. That planet candidate has yet to be confirmed, however, because it's not yet clear whether it is orbiting the star or is merely an object in the distant background. And even if it is a planet, it is an unusually large one — several times the mass of Jupiter — and it orbits a failed star known as a brown dwarf.

The object around GQ Lupi is clearly linked to the star gravitationally.

"The separation between star and planet has not changed from 1999 to 2004, which means that they move together on the sky," Neuhaeuser said. "In our case, we do have a normal plain image showing the bright star and the faint planet a little bit west of the star. The planet is only 156 times fainter than the star, because the planet is still very young and hence still forming, still contracting."

This object "appears to pass" the observational tests "for being a planetary mass companion to its parent star," Jayawardhana said.

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