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.