Exoplanet spotted in motion around its 'sun'

By Katia Moskvitch
Science reporter, BBC News

image captionBeta Pictoris b is located in the constellation of Pictor

Astronomers say they have followed, for the first time, an extra-solar planet in orbit around a young white star.

The team used the European Southern Observatory's Very Large Telescope (VLT) in Chile to track the motion of a gas giant Beta Pictoris b.

The planet's "sun" is also believed to be the youngest star to host a planet.

The find shows that Jupiter-like giants can form near stars in much shorter time-spans than previously thought, the scientists report in Science journal.

Astronomers have so far spotted some 450 extra-solar planets (exoplanets).

But Beta Pictoris b, a gas giant about nine times the mass of Jupiter, is one of only a few to be detected by direct imaging.

It has the smallest orbit of all exoplanets that have been directly imaged so far.

It is also the youngest of them, a co-author of the study, Dr Markus Kasper from the European Southern Observatory, told BBC News.

Its host star, which is also called Beta Pictoris, is very young as well, he said.

It is believed to be around 12 million years old, less than three-thousandths of the age of our Sun.

The new find is located at a distance of 8-15 AU (Astronomical Units) from its parent star - equivalent to the distance of Saturn from the Sun.

This means the scientists should be able to record its full orbit within 15-20 years, said a co-author of the study Mickael Bonnefoy, a student researcher from the University Joseph Fourier in Grenoble, France.

"Further studies of Beta Pictoris b will provide invaluable insights into the physics and chemistry of a young giant planet's atmosphere."

First images

The exoplanet's star is some 60 light-years from Earth, in the constellation of Pictor.

Surrounding it is a debris disc - a dusty gas-rich disc composed of tiny particles that mainly come from collisions of comets with the star.

The team leader Dr Anne-Maris Lagrange from the University Joseph Fourier said astronomers had suspected there was a planet in the disc long before she set out to produce the proof.

She and her team noticed a warp in the disc, a secondary inclined disc and comets close to the star.

image captionAstronomers observed the planet with the Very Large Telescope in Chile

"Those were indirect, but tell-tale signs that strongly suggested the presence of a massive planet, and our new observations now definitively prove this," she said.

The latest results also show that gas giant planets form rapidly within disks - a lot faster than previously assumed.

"The presence of an exoplanet around Beta Pic proves that [gas giants] of about nine Jupiter masses form on a time scale of 10 to 12 million years - very early in the formation of the stars themselves," said Dr Kasper.

The first images of a point-like source in the star's debris disc were obtained back in 2003, but the data was not sufficient to confirm that it was indeed a planet.

The astronomers used the ultra-precise NaCo instrument of the European Southern Observatory's Very Large Telescope in Chile to take more pictures of the disc in 2008 and early 2009 - only to find that the source had disappeared.

It "re-emerged" several months later - on the other side of the disc.

The astronomers then concluded that the "source" was indeed a new giant gas planet bound to Beta Pictoris.

It was not visible during the earlier observations simply because of its constant orbital movement - it was hiding either behind its sun or in its glare in front of it.

Important results

Dr Lagrange said the results of the research gave vital clues about the formation of gas giants, both in our Solar System and beyond.

"The recent direct images of exoplanets… illustrate the diversity of planetary systems," she said.

"Among those, Beta Pictoris b is the most promising case of a planet that could have formed in the same way as the giant planets in our Solar System."

More on this story

Related Internet Links

The BBC is not responsible for the content of external sites.