Credit: T. Riecken/NASA

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You know the planets of our Solar System, each a unique world with its own distinctive appearance, size, and chemistry. Mars, with its bitter-cold, rusty red sands; Venus, a fiery world shrouded in thick clouds of sulphuric acid; sideways-tilted Uranus and its strange vertical rings. The variety is breathtaking.

Now imagine the variety that must exist in hundreds of solar systems. There are worlds out there that make Venus seem hospitable and Jupiter pint-sized.

And to think that only 20 years ago, astronomers were unsure whether any other worlds existed beyond our own Solar System. Now, they've found nearly 290 of them, each with its own planetary personality, each a fascinating example of what a world can be.

Heyday of planetary discovery

Yet the heyday of planetary discovery is only just beginning. In late 2008 astronomers will start a massive search for new planets by observing about 11,000 nearby star systems over a period of six years. This number dwarfs the roughly 3,000 stars that astronomers have searched to date for the presence of planets.

Scientists hope that the NASA-funded project, called MARVELS (Multi-object Apache Point Observatory Radial Velocity Exoplanet Large-area Survey), will find at least 150 new planets, but potentially many, many more.

"We're looking in particular for giant planets like Jupiter," says Jian Ge, principal investigator for MARVELS and an astronomer at the University of Florida in Gainesville, USA. He likens big planets to beacons of lighthouses: signalling the presence of entire solar systems. "Once we find a big planet around a star, we know that smaller planets could be there, too."

MARVELS will do much more than just catalogue a few hundred more planets. By surveying the Jupiter-like planets around such a large number of stars, the project aims to give astronomers the data they need to test competing theories for how planetary systems form and evolve.

To look at so many stars, astronomers will use a telescope that can separately image 60 stars at a time, and this number will eventually be increased to 120 stars. The telescope, which will be housed at the Apache Point Observatory in the Sacramento Mountains of New Mexico, U.S., has a 2.5-metre primary mirror and a wide field of view that covers seven square degrees of the sky; an area that would appear 35 times larger than the Moon.

An array of 60 fibre-optic threads will carry light from the telescope's focal plane to highly sensitive interferometers. These instruments can detect tiny changes in the frequency of a star's light.