Astronomers find 'home from home' - 500 light years away.

ASTRONOMERS have uncovered the first clear evidence that Earth-like planets made from solid rocky material exist outside the Solar System.

A new study of a world 500 light years away, with five times the Earth's mass, has revealed important clues about its internal structure.

Knowing the planet's mass and radius enabled scientists to work out that its density is similar to the Earth's.

This indicates that the planet is solid and rocky rather than mostly gaseous like Jupiter or Saturn.

The planet, known as COROT-7b, was discovered in February this year by the European space telescope COROT. It was detected circling a star now known as COROT-7, towards the constellation of Monoceros, the Unicorn.

The star is slightly smaller and cooler than the Sun and younger, with an age of about 1.5bn years. COROT-7b is only 2.5m kilometres from its parent star - 23 times closer than Mercury is to the Sun.

To calculate the planet's mass, scientists had to make extremely precise measurements of the tugging effect of its gravity on the star.

The data was obtained by the High Accuracy Radial velocity Planet Searcher (Harps), an instrument attached to the European Southern Observatory's 3.6 metre telescope at La Silla, in Chile.

It took 70 hours of observations for the astronomers to collect the information they needed.

Study leader Dr Didier Queloz, from the Geneva Observatory in Switzerland, said "This is science at its thrilling and amazing best. We did everything we could to learn what the object discovered by the COROT satellite looks like and we found a unique system."

COROT-7b orbits its star at a speed of more than 750,000 kilometres per hour, more than seven times faster than the Earth's motion around the Sun.

Temperatures on its "day" face are believed to exceed 2,000C while those on its "night" face may be as low as minus 200C.

CAPTION(S):

An artist''s impression of COROT-7b