Ninety light years away lies a star similar to our own Sun, circled by a giant planet that closely resembles Jupiter in its location, they said.

"This is the closest we have yet got to a real Solar System-like planet, and advances our search for systems that are even more like our own," team leader Hugh Jones of Britain's Liverpool John Moores University, told a conference here.

However, no-one should let their sci-fi fantasies run away with them.

There is no evidence yet that the planet is habitable -- and even if it is, our current rocket technology is so primitive it would take us at least one and a half million years to get there.

The exciting star, HD70642, is located in Puppis, a constellation of stars that make up the stern of the Argo Navis, the ship used by the Argonauts of mythology.

The planet is about twice the mass of Jupiter and orbits HD70642 about every six years, whereas Jupiter takes a dozen years to go around the Sun. In equivalent terms to our Solar System, the planet is about halfway between Mars and Jupiter.

It was discovered using the 3.9-metre (12.7-feet) Anglo-Australian Telescope in New South Wales, Australia, using a technique that measures the "wobble" made by a star when it is subjected to the gravitational tug of a large passing mass.

The presentation was made at a conference on extrasolar planets organised by France's Institute of Astrophysics. The paper has been accepted for publication by the Astrophysical Journal, the organ of the American Astronomical Society.

The discovery is part of a loose-knit programme to sniff out "extrasolar" planets.

So far more than a 100 of these phenomena have been detected since 1995, and each new piece of information is helping to build a picture that is remarkably varied.

Previously, the thinking was that extrasolar systems would be like ours.

In our case, there are four solid planets -- Mercury, Venus, Earth and Mars -- that are in relatively close orbits to the Sun.

After that come the "gas giants," respectively Jupiter, Saturn, Uranus and Neptune (Pluto is solid, but its size and orbit have prompted many astronomers to privately declassify it as the ninth and outermost planet of the Solar System and to consider it a large chunk in the Kuiper Belt, a distant ring of orbiting rubble).

These gas giants are thought to have a vital nurturing role in the formation of the rocky planets that lie closer to the Sun and where human life is possible. Jupiter also plays the role of guardian, taking impacts from comets or giant space rocks that could wipe out life on Earth.

But the evidence shows that extrasolar systems can be very diverse, and not at all like our own.

Indeed, most of the extrasolar planets found so far have egg-shaped orbits, which implies temperature extremes that would make it uninhabitable for humans, or they are otherwise freezingly far or scorchingly close to their sun.

The latest discovery is intriguing because of the planet's similarity to Jupiter, especially its location relative to HD70642.

This raises the possibility that in closer orbit are rocky planets that -- who knows? -- may be Earth-like, although it would be difficult to detect the smaller "wobble" they would exert on the star.

But advances, in sensors and mathematics, are being made all the time in this new frontier of astronomy.

"It is the exquisite precision of our measurements that lets us search for these Jupiters -- they are harder to find than the more exotic planets found so far," Alan Penny, from Britain's Rutherford Appleton Astronomy, said.

"Perhaps most stars will be shown to have planets like our own Solar System."

SPACE.WIRE