Astronomers discover first proof that there are other solar systems like ours

Astronomers have found a planet in another solar system that bears an uncanny resemblance to Jupiter, raising the prospect that we might one day discover a twin to Earth.

The latest "exoplanet" beyond our own solar system is similar in size to Jupiter, the largest of the known planets, and travels in a similar orbit around a star that is very like the Sun.

The techniques used to identify the planet are not yet refined enough to pick out smaller, Earth-sized planets but astronomers believe new space-based telescopes may one day take pictures of other worlds where life exists.

Scientists had never before identified an exoplanet orbiting at a distance from its own star similar to that between the Sun and Jupiter. The find is proof that other solar systems like ours do exist.

Geoffrey Marcy, a professor of astronomy at the University of California, Berkeley, and Paul Butler of the Carnegie Institution of Washington in Pasadena, said the find reminded them of our own solar system. "All other exoplanets discovered up to now orbit closer to the parent star, and most of them have had elongated, eccentric orbits. This new planet orbits as far from its star as our own Jupiter orbits the Sun," said Professor Marcy.

The planet is a "gas giant" like Jupiter but is between three and a half and five times bigger. Its elongated orbit takes it around its star – 55 Cancri in the constellation Cancer – once every 13 years, compared with the 11.86 years it takes for Jupiter to orbit the Sun.

Mr Butler and Professor Marcy have been searching for other planets for more than 15 years and have pioneered a technique of analysing the "wobble" of a star caused by the gravitational pull of a passing planet. Since the first exoplanet was identified in 1995, some 90 planets beyond our own solar system have been confirmed. All, however, are orbiting too close to their stars to support life. One of the objects of the search for exoplanets is to find a rocky, Earth-like planet orbiting in the "Goldilocks" zone, which is neither too hot nor too cold for liquid water.

Dr Butler said a project to monitor 1,200 stars could one day reveal a solar system even more similar to our own.

The latest Jupiter-like planet is about 511 million miles from its star, compared with the 512 million miles between Jupiter and the Sun and the 93 million miles separating Earth from the Sun. It has a slightly elliptical orbit, compared with the circular orbit of Jupiter.

Working with Debra Fischer from the University of California, Berkeley, the Butler-Marcy team announced the discovery of 13 exoplanets including the smallest so far – a planet in the constellation Auriga that is about 15 per cent of the mass of Jupiter.

The scientists used telescopes at the Lick Observatory in California to make their discoveries. A number of space telescopes are needed for the search for Earth-like planets.