Youngest exoplanet discovered - and it grew up fast

Posted by Emma Woollacott

Images of an alien planet passing in front of its sun have demonstrated that gas giants can form very quickly.

It's the first time astronomers have been able to directly follow the motion of an exoplanet as it moves from one side of its host star to the other.

Only 12 million years old, Beta Pictoris is located about 60 light-years away towards the constellation of Pictor, and is surrounded by a dusty debris disc.

Earlier observations showed a warp of the disc, a secondary inclined disc and comets falling onto the star.

"Those were indirect, but tell-tale signs that strongly suggested the presence of a massive planet, and our new observations now definitively prove this," says team leader Anne-Marie Lagrange.

"Because the star is so young, our results prove that giant planets can form in discs in time-spans as short as a few million years."

The team used the NAOS-CONICA instrument (NACO) on ESO's Very Large Telescope (VLT), to study the immediate surroundings of Beta Pictoris. In 2003 a faint source inside the disc was seen, but it wasn't possible to exclude the possibility that it was a background star.

But in images taken in 2008 and spring 2009 the source had disappeared - and in fall 2009, the object appeared again on the other side of the disc.

This confirmed that it really was an exoplanet orbiting its host star. It also showed that the planet has the smallest orbit of any of the ten exoplanets discovered so far, at about the distance of Saturn from the Sun.

"Together with the planets found around the young, massive stars Fomalhaut and HR8799, the existence of Beta Pictoris b suggests that super-Jupiters could be frequent byproducts of planet formation around more massive stars," said team member Gael Chauvin.