Astronomers track nearby planet

Epsilon Eridani: Its planet could be viewed by Hubble

By BBC News Online science editor Dr David Whitehouse

Astronomers have discovered a planet orbiting the star Epsilon Eridani.

The relative proximity to Earth - just 10.5 light years away - means this is the closest star yet to have a planet found circling about it.

This raises the exciting possibility that the Hubble Space Telescope may be able to obtain an image of the planet.

Were this to happen, it would be an astronomical landmark as it would be the first planet actually seen circling another star.

The discovery will be announced at the International Astronomical Union's General Assembly in Manchester, UK, on Monday.

Larger than Jupiter

The planet orbiting Epsilon Eridani, a star very similar to our own Sun, was found by a team led by Dr William Cochran, of the University of Texas McDonald Observatory.

The planet orbits Epsilon Eridani from a distance of about 500m km (300m miles) - roughly the distance from the Sun to the asteroid belt in our own Solar System.

Researchers estimate that the planet is probably just larger than Jupiter, the largest planet in our Solar System.

Epsilon Eridani is a star slightly less massive than our Sun and slightly cooler.

It is most probably younger as well, being only about one billion years old compared with our Sun's age of 4.5bn years.

Earth-sized planets

Dr Cochran said of the discovery "is like finding a planet in our own backyard, relatively speaking."

"Not only is this planet nearby, it lies 478 million kilometres (297 million miles) from its central star," Cochran said.

"Having a large planet orbiting a fair way out from Epsilon Eridani means there could be room for Earth-like planets in a reasonably stable orbit closer into the star.

"All the planets found so far that are the size of Jupiter are much closer to the parent star."

Viewed from Earth

It may be possible to view the new exoplanet with the Hubble Space Telescope or with the new generation of advanced imaging systems connected to ground-based telescopes.

If the planet could be seen as a tiny speck of light next to the artificially suppressed image of its parent star, it would be a major scientific achievement - the first time an image of a planet circling another star would have been obtained.

With such an image, astronomers could analyse the light from the planet and determine its physical characteristics and composition.

To date, current imaging technology has forced astronomers to use indirect methods to detect the presence of planets around stars. This can involve looking for a tell-tale "wobble" in the parent star - behaviour that can be explained only by the gravitational effects associated with a planet-sized body circling nearby.