The threat of space rocks smashing into Earth is bigger than previously thought, say scientists studying the terrifying meteor that exploded without warning over a Russian city last winter.

An out of control satellite, the size of a bus, is due to hit the earth this evening, it is still not known where.

A small meteorite or piece of man-made space junk may have struck the Columbia shuttle while it was still in orbit causing it to crash on its return to earth, Nasa said today.