Planet 'just right' to support life discovered

Not too far from its star, and not too close, so it could contain

liquid water. The planet itself is neither too big nor too small for the proper surface, gravity and atmosphere. Just like Earth.

"This really is the first 'Goldilocks' planet," said co-discoverer R Paul Butler of the Carnegie Institution of Washington.

The planet circles a star called Gliese 581, about 120 trillion miles from Earth. It sits in the middle of what astronomers refer to as the habitable zone, unlike any of the nearly 500 other planets astronomers have found outside Earth's solar system.

The planet is about three times the mass of Earth, slightly larger in width and much closer to its star.

Temperatures can be as hot as 71C or down to minus 4C, but in between it would be "shirt-sleeve weather", say scientists.

Because conditions are ideal for liquid water, and because there always seems to be life on Earth where there is water, they believe "that chances for life on this planet are 100 per cent".