The first planet that could support life as we know it outside our solar system has been discovered.
A team of European astronomers say they have detected a rocky world, possibly only 50 per cent larger than the Earth, circling a small red star called Gliese 581, 20.5 light years away in the constellation Libra.
What makes the discovery so important is that the planet orbits in what astronomers call the "Goldilocks zone" – where makes it neither too hot, nor too cold for life.
Astronomers have found more than 200 planets circling other stars, but, until now, all have been unsuitable for life because they are either massive gas balls, resembling Jupiter, that circle scorchingly close to their parent, stars, or have eccentric orbits that take them out into the bitterly cold depths of space.
The newly found "super-Earth," about five times more massive than our planet, is 14 times closer to its star than the Earth is from the sun. As a result, its year lasts only 13 Earth days. It has been named , named 581 c.
However, because the star is only a third the mass of our sun, it is also much cooler.
Astronomers estimate that the world's surface temperature would therefore be between 0 and 40 degrees.
"Water would thus be liquid," one of the discoverers, Stephane Udry, from Switzerland's Geneva Observatory, said.
"Models predict that the planet should be either rocky – like our Earth – or covered with oceans."