Rosetta homes in on rare asteroid

A UK-backed space probe will visit a peculiar potato-shaped world tomorrow night to find out clues about how planets formed. Europe’s $1.5 billion Rosetta spacecraft flies past the three-mile wide asteroid Steins at around 8pm UK time, Friday evening, four and a half years after it was launched from French Guiana.

The three-ton, unmanned ship will pass around 500 miles from Steins which is one of the rarest types of asteroid and thought to be a fragment of a much larger one that broke up.

Scientists believe it is older than the planets and similar to the material that collected to form worlds like the Earth more than four billion years ago.

During its flypast, Rosetta will make accurate photos and measurements of the asteroid’s size, shape and volume. It will also check whether Steins has any mini moons of its own.

The encounter will happen 224 million miles away from Earth and results will take 20 minutes to reach us when they are radioed back across space.

Following the flyby, Rosetta will head for another asteroid called Lutetia in 2010 and then on to a final rendezvoud with a comet called Churyumov-Gerasimenko in 2014. It will go into orbit around the comet and try to land a probe on it.

Rosetta has been bouncing around the solar system during its long flight, gaining momentum from close passes to the Earth and Mars. It sent home stunning images of our own planet during one flyby. Last year, in an embarrassing moment false alarm for astronomers, it was itself mistaken for a threatening asteroid when it was spotted heading for a planned close approach.

There is much UK involvement from industry and science in the Rosetta mission. Several companies helped build the probe and scientists from universities on the mainland and Northern Ireland are involved in ten of its 21 experiments.