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Friday, July 30, 1999 Published at 12:02 GMT 13:02 UK


Planet discovered orbiting Sun-like star

The wobble that betrays the presence of a planet

By BBC News Online Science Editor Dr David Whitehouse

A new planet with an Earth-like orbit has been found by astronomers at the European Southern Observatory in South America.

It is circling a star that is very similar to our Sun and is just visible to the unaided eye at a distance of 56 light-years in the southern constellation of Horologium or the Pendulum Clock.

The discovery came about following a long-term survey of forty solar-type stars that was begun in November 1992.

It measured stellar radial velocities, that is the speed with which a star moves towards and away from the Earth. This way the slight wobble caused by an orbiting planet can be detected.

The new planet, called iota Hor b, has an orbital period of 320 days and is about 2.26 times more massive than Jupiter, the largest planet in our solar system.

It revolves around its host star in a somewhat elongated orbit. If it were located in our own solar system, this orbit would stretch from just outside the orbit of Venus to just outside the orbit of the Earth.

Of all the planets discovered so far, the orbit of iota Hor b is the most Earth-like.

The new planet is probably a gas-giant which means that if life did develop in its atmosphere it would be unlike life on Earth. It is possible that the new world has moons which could be favourable places for life to start.

The astronomers say that the high scatter of the data points in their radial velocity measurements of the star suggests that there may be the signal from another planet in the data.

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