Clouds of dust around a young star are beginning to form into planets say astronomers.

Although scientists believe they know in broad outline how planets are formed out of gas and dust that surround some young stars there is still a lot of detail that is not understood.

New observations of three stars may have filled some of the gaps about how planets form. Henry Throop of the University of Colorado at Boulder believes that he may have found a "birthing star".

A dust disk around a "birthing star"

It may be a previously unseen stage in the formation of planets - the link between space dust and large planets.

The stars are 1500 light years distant in a stellar nursery called the Orion nebula. Hubble Space Telescope images of some of the new-born stars in this region have revealed discs of large particles around them.

The particles are about 100 times larger than normal space dust and have apparently grown by the accumulation of smaller grains.

"This is the first time scientists have been directly able to see the accretion process in the formation of planets," said Mr Throop.

When stars forms from a cloud of gas and dust they ignite when the temperature and pressure inside them become great enough for nuclear reactions to occur.

Left around the young star is a disc of leftover gas and dust that can form into planets.