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Monday, 12 February, 2001, 19:05 GMT
At a glance: Asteroid touchdown
BBC/Nasa Near-Shoemaker ends its five-year journey
Near-Shoemaker ends its five-year journey
The Near spacecraft is ending its mission with an historic descent on to the surface of an asteroid.

Near-Shoemaker began its life as simply Near: Near Earth Asteroid Rendezvous. It was renamed Near-Shoemaker in 2000 after geologist Gene Shoemaker, who died in a car accident in 1997. Shoemaker was studying asteroid impact craters in Australia and once said he would like to take a geologist's hammer to Eros.

The probe was launched on 17 February, 1996, from Cape Canaveral in Florida. Its trip to Eros was delayed by a year and 23 days in 1998 when controllers were unable to manoeuvre it into the correct orbit.

The craft is about the size of a car, though it looks like an oversized gold-coloured dustbin with four solar panels extended at one end.

Near Shoemaker is the first of the Discovery series of spacecraft - built as part of the American space agency's (Nasa) "faster, better, cheaper" programme. Subsequent missions will analyse the solar wind, three comets and the planet Mercury.

Eros, otherwise known as Asteroid 433, was chosen as a destination because it is relatively big and close to Earth. It is thousands of times bigger than some of its neighbours and part of a group known as the near-Earth asteroids. They are believed to have broken away from the main asteroid belt between Mars and Jupiter and are our nearest neighbours in space after the Moon.

Near is providing important information on the structure and composition of asteroids, which would be needed for any future attempt to deflect an Earth-bound asteroid. Scientists would need to know where the centre of gravity of any incoming asteroid was and how hard to hit it to deflect it without splitting it up.

The gravity on Eros is very weak, but was still strong enough to hold Near-Shoemaker in orbit for a year. A person weighing 90 kg on Earth would weigh around 50 g on Eros and someone who could jump a metre in the air on Earth would be able to jump well over a kilometre and risk entering orbit.

The temperature on Eros is estimated to vary between 100 degrees Celsius during the day and 150 below zero during the night.

The functioning equipment on the probe includes a device to measure the asteroid's magnetism, a spectrometer to examine its composition, an electronic camera and a laser rangefinder to survey its precise shape.

Near is the first Nasa planetary mission controlled by a non-Nasa space centre. The mission operations centre is the John Hopkins University Applied Physics Laboratory.

Signals from Near-Shoemaker take around 15 minutes to reach Earth.

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