Published online 7 January 2003 | Nature | doi:10.1038/news030106-4


29 hours is a year on OGLE-TR-56b

Most distant planet orbiting another star spotted in passing.

The newfound planet is shrouded in clouds of iron atoms.The newfound planet is shrouded in clouds of iron atoms.© D.A. Aguilar, Harvard-Smithsonian Center for Astrophysics.

Astronomers have found the most distant planet orbiting another star. It is also the fastest yet found - its year lasts a mere 29 hours.

The planet is 5,000 light years away, towards the centre of our Milky Way, and 20 times further than the previous record holder.

The planet, called OGLE-TR-56b, is fourteen times closer to its star than Mercury is to the Sun, its discoverers told this week's American Astronomical Society meeting in Seattle. "It's a very strange orbit," says Dimitar Sasselov of the Harvard-Smithsonian Center for Astrophysics, who led the team.

The discovery might open the way for finding planets similar to Earth. OGLE-TR-56b is the first planet astrophysicists have discovered by watching it pass in front of the star that it orbits, a phenomenon called transiting.

Based on the 1% dimming in the star's brightness, the team believe the new planet is about the size of Jupiter.

Only planets in solar systems that are side-on to us will have orbits that obscure our view of their stars. One other planet has been shown to do this, but it was first spotted using the traditional method of measuring its gravitational pull on its parent star.

Transiting should be much more sensitive than the gravitational technique, but several years of searching had yielded nothing. "People were getting desperate," says Sasselov.

“This is going to quieten the detractors down quite a bit”

Scott Gaudi
Institute for Advanced Study, Princeton

The lack of success had drawn criticism, says Scott Gaudi of the Institute for Advanced Study in Princeton, who is also searching for transiting planets. "This is going to quieten the detractors down quite a bit," he says.

Now that we know the method works, says Sasselov, we can be confident of finding small, Earth-like planets orbiting nearby stars at distances where life might survive. The Kepler space mission, due for launch in 2007, could find as many as 20 candidates in its first five years of operation, Sasselov believes. 

Institute for Advanced Study, Princeton