Scientists at the Geneva Observatory have discovered a new planet circling a star almost identical to our Sun.

It is the eighteenth planet known to be orbiting another star but is important because the mass of the new planet is similar to that of Saturn in our solar system. Previously discovered extra-solar planets have been somewhat larger.

At the moment astronomers are not able to detect Earth-sized planets around other stars. But they argue, if Jupiter and Saturn-sized planets exist, then it is likely that there are Earth-sized ones as well.

Major aim

Detecting an Earth-like planet is one of the major goals of Nasa's future space missions. Several designs of space observatories with this aim are being prepared for launch during the next 10-15 years.

Scientists have not obtained a picture of the new planet. That is not possible because of the glare of the star it is orbiting. Its presence was revealed through its slight gravitational effect on its parent star's motion. The star, called HD 75289, is in the southern sky and is 70 light years distant.