Astronomers in America yesterday announced the strongest evidence to date that our own nine-planet solar system is not alone.
They are due to publish results of two independent studies showing that there are at least three planets orbiting the star Upsilon Andromedae.
The star is 44 light years from Earth and was already known to have one planet, discovered in 1996.
The discovery of two further planets is the culmination of 11 years of telescope surveys designed to look for a star's "wobble", caused by the gravitational pull of orbiting planets.
It is the first hard evidence that the universe could be teeming with planets and solar systems, given that the first planet was found after a survey of just 107 stars - a minute fraction of the 200 billion stars in our own galaxy, the Milky Way.
The discovery of the first solar system beyond the Sun was made independently by scientists at San Francisco State University, Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts, and the High Altitude Observatory in Boulder, Colorado. The work is due to be published in The Astrophysical Journal.
Debra Fischer, an astronomer at San Francisco State University, said that the discovery of three planets orbiting a single star opened up possibilities for further finds.
"It implies that planets can form more easily than we ever imagined, and that our Milky Way is teeming with planetary systems," said Dr Fischer.
Observations so far indicate that all three planets are giant worlds, equivalent in size to Jupiter, the biggest planet in the solar system.
The innermost planet of Upsilon Andromedae is at least three-quarters of the mass of Jupiter and orbits at a distance of less than a tenth of that between Earth and the Sun, making its "year" just 4.6 days long.
The middle planet is at least twice the size of Jupiter and takes 242 days to orbit the star; the outermost planet - a massive world - is at least four times bigger than Jupiter and takes between 3.5 and 4 years to complete its stellar orbit.
Because instruments used in the research were not sensitive enough to detect small bodies, scientists have not ruled out the possibility that the newly discovered solar system also contains Earth-sized planets.
Discovering three Jupiter-sized planets around one star has puzzled scientists, who say that the phenomenon is not easy to explain by current theories of planet formation.
"This will shake up the theory of planet formation. A question was whether the massive bodies orbiting stars really were planets, but now that we see three around the same star, it is hard to imagine anything else," said Robert Noyes, professor of astronomy at the Harvard-Smithsonian Centre.
The scientists are convinced that their observations reflect a genuine discovery because they have been made independently by two groups, said Sylvain Korzennik, a member of the Harvard-Smithsonian team.
Dr Fischer agreed: "Having two completely independent sets of observations gives us confidence in this detection."
After finding the initial "wobble" that led to the discovery of the first planet, the scientists found other movements of the star, which could only be explained by the presence of a second and third planet.
"We looked at the two-planet solution [but] there was still too much extra noise. We concluded that the extra wobble could only be explained by the presence of a third planet," said Dr Fischer.Reuse content