Planet systems come into view

The Milky Way may be "teeming" with Earth-like planets, according to astronomers who have discovered three planets in orbit around a relatively nearby star. This is the first planetary system found outside our own Solar System and suggests that collections of planets may be more abundant than realised.

"It implies that planets can form more easily than we ever imagined, and that our Milky Way is teeming with planetary systems," stated Dr Debra Fischer of San Francisco State University.

The star in question is Upsilon Andromedae, about the same size as the Sun but an estimated 1.5 billion years younger. It is a mere 44 light years away, a close neighbour as astronomical distances go. The trio of planets are real heavyweights, however, great hulking giants more like Jupiter than the Earth.

The innermost planet, which in fact was discovered three years ago, has three-quarters the mass of Jupiter but sits cheek-by-jowl with Upsilon Andromedae, fewer than six million miles out and able to complete an orbit in just 4.6 days. By contrast, the Earth orbits the sun at 93 million miles.

The newly-discovered second and third planets are twice the size and four times the size of Jupiter respectively. The big fellow in the back row orbits once every 3.5 to four years.

Astronomers have been on the hunt for distant planets for years but only in recent times have systems improved to the degree that they can be identified. A small collection of stars are known to have single large planets in orbit but this is the first with a clutch of planets in tow.

NASA hopes to launch a new spacecraft, SIM, in 2005. SIM will spend five years in orbit probing nearby stars for signs of Earthsized planets.