Scientists have discovered a planet not much bigger than Earth that could be covered in oceans and has the right temperature to support life. And it is only 20.5 light years away.

By 2020, it should be possible for a telescope to take a close look at the planet, which has not yet been named, to see if there is any sign of life.

The newly found planet is older than our solar system. It is revolving around the star known as Gliese 581, a red dwarf in the Libra constellation. Its year lasts only 13 days because it is 14 times closer to its star than the Earth is to the Sun. But that is a good sign, because red dwarfs are less than half the size of the sun, and cooler.

In the zone where the planet has been discovered, surface temperatures would be between 0C and 40C - just right for oceans to have formed and life to have begun.

It is the smallest planet yet discovered outside the solar system, with a radius about one and a half times that of Earth giving it about twice the gravitational pull. Any living creatures on it would need thick bones and sturdy legs because they will be twice as heavy as on Earth.

Dr Malcolm Fridlund of the European Space Agency said: "This is an important step on the road to finding Earth-like planets. The planets we've found so far outside the solar system have all been more like Jupiter or Neptune. If this is a rocky planet it's likely that it will have liquid water on its surface, which means there may also be life.

"There are caveats, one being that the environment around a red dwarf is full of radiation. All red dwarfs have a lot of flare activity, but this doesn't necessarily exclude life."

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