BBC NEWS | Science/Nature | Small planets seen by astronomers

US astronomers say they have found two more Neptune-sized planets orbiting stars beyond our Solar System.

They say their discovery of the smallest worlds yet seen circling other stars is a breakthrough in the search for other Earths and for life in space.

They are only about 15 times more massive than the Earth. Previously known worlds were Jupiter-class, some 318 times more massive than the Earth.

One of the new planets is in the first four-planet system ever discovered.