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Wednesday, February 10, 1999 Published at 16:25 GMT


Pluto passes Neptune

Pluto and its moon Charon

By BBC News Online Science Editor Dr David Whitehouse

A rearrangement of the Solar System's outer planets is about to take place as tiny Pluto regains is crown as the most distant planet.

For such a small and distant world, Pluto has been the centre of attention over recent months.

A debate about reducing its status as a true planet had astronomers all over the world saying that Pluto should not be demoted.

[ image: Our best map of Pluto]
Our best map of Pluto
As if by way of a reply, at 1122 GMT on Thursday, Pluto crosses the orbit of Neptune and once again becomes the furthest planet from the Sun.

Pluto, discovered in 1930, follows an elliptical orbit around the Sun taking 248 years for one revolution.

For a few years each orbit, it comes closer to the Sun than Neptune, the next furthest planet.

This happened on 7 February, 1979, when it crossed Neptune's path moving sunward. Pluto reached its closest point to the Sun on 5 September, 1989, when it was 4.4 billion km (2.7 billion miles) from it.

Astronomers plan no ceremony when Pluto regains its title but they do hope that the renewed interest in the world will boost their chances of sending a spaceprobe to visit it.

There is no danger of a collision between Pluto and Neptune. Their orbits are synchronised so that they are never in the same place at the same time.

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