Nasa probe set for first landing on an asteroid

Controlled descent' on to Eros today is a 'bonus' finale to a mission which aims to uncover the secrets of our solar system's birth

A duet in space that began last St Valentine's Day is about to culminate in a delicate kiss when a space probe lands on an asteroid named after the god of love. Eros, a potato-shaped lump of rock the size of central London, has been flirting with the orbiting Near-Shoemaker spacecraft since last February, but today the dalliance will come to an exciting climax.

A duet in space that began last St Valentine's Day is about to culminate in a delicate kiss when a space probe lands on an asteroid named after the god of love. Eros, a potato-shaped lump of rock the size of central London, has been flirting with the orbiting Near-Shoemaker spacecraft since last February, but today the dalliance will come to an exciting climax.

The first "controlled descent" on to an asteroid will take place after a series of four engine burns brings the Near-Shoemaker probe from its position 22 miles from Eros to land - hopefully softly - on its hard surface. The US National Aeronautics and Space Administration (Nasa) said the probe had gathered more than enough data during its year-long orbit and now was the time to test its ability to land safely.

When the project began four years ago, Andrew Cheng, the project scientist at the Applied Physics Laboratory at the Johns Hopkins University in Baltimore, said the probe should begin to resolve some of the mysteries about asteroids. Are they solid rocks or lumps of "builder's rubble" left over from the birth of the solar system? More recently, Dr Cheng said: "We have answered the question we had when the orbit began. We now know that Eros is a solid body of uniform composition, made of material probably older than the Earth. But we also found other things we didn't expect to see and have questions we didn't know to ask at the start of the mission. Scientists will be looking at this data for years."

Nasa has planned a complex sequence of manoeuvres that will take the space probe out of its current orbit and into a gradual descent to the "saddle", a distinctive depression six miles wide in the centre of the asteroid. "If everything goes to plan, the spacecraft will land without any damage and send a signal beacon back to Earth telling us it has arrived. Unfortunately, it won't be able to carry on collecting scientific data," said Mike Buckley, a spokesman for Johns Hopkins University.

Eros's "saddle" has intrigued the scientists, who should be able to get close-up photographs of objects that are just four inches wide as the space probe comes in to land.

The techniques learnt during the landing will also help scientists to plan other landing missions to asteroids. Some have speculated that these could be useful if asteroids were to be mined for their mineral-rich resources, or in the event of them having to be blown off course if they threatened to collide with Earth.

"With the spacecraft just about out of fuel and our science objectives met, this is a great way to end a successful mission," said Robert Farquhar, Near-Shoemaker's director. "It's all bonus science. It's never been tried before and it certainly is a complicated set of manoeuvres, but at this point the only real risk is not taking one," he said.