'Tatooine-like' double-star systems can host planets

An artist's impression depicts the two relatively small planets orbiting
a binary in the constellation Cygnus 

A new study shows that planetary systems can form and survive in the chaotic environment around pairs of stars.

A team reports in Science the discovery of two planets orbiting a pair of stars - a so-called binary.

Gravitational disturbances generated by stellar pairs are thought to be very severe for any orbiting planets.

Nasa's Kepler space telescope found two small planets around a pair of low-mass stars.

Such systems have particular significance for science fiction fans. In the Star Wars films, Luke Skywalker's home planet of Tatooine orbits a binary star.

The planetary system, known as Kepler-47, is located roughly 5,000 light-years away, in the constellation Cygnus.

It contains a pair of stars whizzing around each other every 7.5 days. One star is Sun-like, while the other is about one-third the size of its neighbour and 175 times fainter.

Circling the stars is an inner planet about three times larger in diameter than the Earth, and an outer planet that is just slightly larger than Uranus.


The inner planet - dubbed Kepler-47b - takes 49 days to complete an orbit, while the outer planet - Kepler-47c - takes 303 days.

The orbit of the outer planet places it in the so-called "habitable zone", the region around a star where it is neither too cold nor too hot for liquid water to persist on the surface of a planet.

While the outer world is probably a gas-giant planet and thus not suitable for life, its discovery establishes that these "circumbinary" planets can, and do, exist in habitable zones.

-  BBC.co.uk