By Alexia Vlahos
SANTIAGO (Reuters) - Scientists searching for a planet like Earth said on Tuesday they have found the smallest planet ever detected outside the solar system, less than twice the size of our own.
The exoplanet, a planet that orbits a star beyond the solar system, is called Gliese 581e after the star it circles. Because of its relatively small size it is likely rocky, like Earth, as opposed to gas giants such as Jupiter or Saturn, the astronomers said.
"It is the lightest planet detected outside the solar system so far," Dr. Gaspare Lo Curto, an astronomer at the European Organization for Astronomical Research in the Southern Hemisphere, told a news conference.
"We are not too far away from finding a planet like Earth," he added.
Gliese 581e orbits its star in just 3.15 days, but lies outside a so-called "habitable zone" and could not sustain life, Lo Curto said. Its mass is just 1.9 times that of Earth, and it is 20.5 light years away.
But while the small planet is outside the habitable zone, the biggest of three other previously discovered planets in the same system appears to be inside this just-right zone.
"The most outlying planet is inside what is defined as a habitable zone, which is a zone where there could be water in a liquid state on the surface of the planet," Lo Curto said.
The international team of researchers used a 3.6 meter telescope at the Paranal Observatory in La Silla, 370 miles north of Chile's capital Santiago. Their findings are also being presented to an astronomical meeting this week in Britain.
Around 340 exoplanets have so far been found orbiting other stars besides the Earth's sun, most of them gas giants with characteristics similar to Jupiter and Neptune.
(Editing by Simon Gardner and Vicki Allen)
Scientists have made two major discoveries in the search for other Earth-like planets. British astronomers say they have discovered the smallest known Earth-like exoplanet orbiting a living star called Gliese 581 e and also discovered that a nearby planet called Gliese 581 d, discovered in 2007, is in the much sought after 'habitable zone'. Astronomers also believe there is a possibility that 581 d could have liquid oceans on its surface, calling the find "extraordinary."
Artist's impression of the planetary system around the red dwarf Gliese 581. 
"The Holy Grail of current exoplanet research is the detection of a rocky, Earth-like planet in the 'habitable zone'," said astrophysicist at Switzerland's Geneva University, Michel Mayor.

Astronomers say 581 e is 20.5 light years away from Earth and that it's roughly 1.9 times larger than Earth, making it the smallest exoplanet discovered to date. It was found using the High Accuracy Radial Velocity Planet Searcher (HARPS). It orbits too close to its parent star, Gliese 581, which would make it too hot, unable to support life as we know it. It takes just over 3 days for it to orbit the star.

Exoplanet 581 d, however, is another story. Astronomers say this makes it possible to not only support life, but have liquid water in the forms of oceans. 581 d is approximately 7.7 times larger than Earth. Astronomers originally thought it was too cold to have liquid water thus would not be able to host Earth-like life.

"It is very exciting that such a promising candidate for an Earthlike planet has been found so close to us. It means there are likely to be many more when we search further," added Mayor.