Earth-like planet discovered surrounding a star.

An Earth-like planet that could be covered in oceans and may support life has been discovered outside the Solar System.

The new world, which is 20.5 light years away, orbits a region with the right temperature to allow liquid water on its surface.

Scientists believe it is only 1.5 times larger and five times more massive than Earth, making it the smallest extra-solar planet known.

But the really exciting discovery is that the planet inhabits the habitable zone of its parent star, Gliese 581.

Also known as the "Goldilocks zone", this is the narrow orbit in which temperatures are not too hot, not too cold, but just right for surface water to exist as a liquid.

The habitable zone varies according to the heat output of the star, and Gliese 581 is much smaller and colder than the Sun. So even though the planet is 14 times closer to the star than the Earth is to the Sun, it lies in a region where rivers, lakes and oceans are possible.

Liquid water is one of the pre-requisites for life as we know it on Earth.

The planet was found by Swiss, French and Portuguese astronomers using the European Southern Observatory's 3.6 metre telescope at La Silla in Chile.

They employed a method of long-distance planet finding that looks for the "wobble" on a star caused by the gravity of a large object orbiting it.

By measuring the wobble motion, shown as shifts in the star's light spectrum, astronomers can calculate a planet's orbit and mass.