Washington, Jul 31 (IANS): Astronomers using a NASA telescope have confirmed the discovery of the nearest rocky planet outside our solar system which is larger than Earth and a potential gold mine of science data.

Dubbed HD 219134b, the exoplanet, which orbits too close to its star to sustain life, is mere 21 light-years away.

It is also the closest exoplanet to Earth to be detected transiting, or crossing in front of, its star and, therefore, perfect for extensive research.

"Transiting exoplanets are worth their weight in gold because they can be extensively characterised," said Michael Werner, project scientist for the Spitzer telescope mission at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

Rocky planets such as this one, with bigger-than-Earth proportions, belong to a growing class of planets termed super-Earths.

"Most of the known planets are hundreds of light-years away. This one is practically a next-door neighbour," said study co-author Lars A. Buchhave of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

HD 219134b was determined to have a mass 4.5 times that of Earth, and a speedy three-day orbit around its star.

Now that astronomers know HD 219134b transits its star, scientists will be scrambling to observe it from the ground and space.

The goal is to get chemical information out of the dimming starlight as the planet passes before it.

If the planet has an atmosphere, chemicals in it can imprint patterns in the observed starlight.

The planet, initially discovered using HARPS-North instrument on the Italian 3.6-metre Galileo National Telescope in the Canary Islands, is the subject of a study accepted for publication in the journal Astronomy and Astrophysics.