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Monday, September 28, 1998 Published at 12:07 GMT 13:07 UK


Closing in on a comet

Rosetta is being designed to land on a comet

By our science editor David Whitehouse

As a picture it is not very impressive but the tiny smudge of light picked up by one of the world's most powerful telescopes will eventually become one of the most famous objects in the sky.

The newly-built Very Large Telescope at the Paranal observatory in South America turned its gaze towards dim and distant comet Wirtanen as part of its evaluation phase.

It is a faint patch light, a small object but it will eventually become one of the most studied objects in space.

Scientists are building an ambitious spacecraft to fly to comet Wirtanen and land on it - but it will not be easy to do.

[ image: Far out: Comet Wirtanen]
Far out: Comet Wirtanen
A comet is a flying mountain of ice and rock, in Wirtanen's case only about 1 km (0.6 mile) across. This means that it has very little gravity making the design of a craft to land on it rather tricky.

The comet rendezvous and landing mission is called Rosetta and is due for launch in 2003.

To send it on the correct trajectory a close watch needs to be kept on Wirtanen.

Wirtanen is one of the smallest comets know but, for its size, one of the most active.

Spending most of its time in the cold outer reaches of the solar system it is a frozen snowball that occasionally blasts out into space gas and dust.

When it catches up with Wirtanen in 2012 Rosetta will fly in formation with it for 18 months.

Comets are important because they are leftovers after the formation of the solar system made of material unchanged since before the sun was born four and a half billion years ago.

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