Astronomers based in Geneva have discovered five new planets outside our solar system. The planets cannot be seen directly but were detected by the gravitational pull they exert on their host stars.This content was published on August 7, 2000 - 18:11
The most significant discovery concerns one planet, named HD 83443c. It is the lightest planet ever discovered outside the solar system, with a mass roughly half that of Saturn. It is also only the second planet ever found which is part of a multi-planet system.
The discoveries, formally announced on Monday, were made by a team of astronomers from the Geneva observatory. They found the planets after examining information gathered by the La Silla Observatory in Chile.
Because planets produce no light of their own, they can only be detected by the gravitational pull they exert on the stars they orbit. Measurements of the minute effects planets have on their host stars allows astronomers to calculate a planet's orbit as well as its mass.
So far around 50 extra-solar planets have been discovered, but because they can only be detected by the effect they have on their stars, all are far bigger than Earth, and most are the size of Saturn or larger.
Such planets are almost certainly composed mainly of gas, with a rocky core. Like the gas giants of the solar system - Jupiter, Saturn, Uranus and Neptune - they are unlikely to be unable to support life.
The planet HD 83443c circles the star HD 83443, along with two Saturn-sized gas giants. The system is 141 light years from our Sun and lies in the Vela constellation.
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