He was then hit over the back of his head with a heavy object - possibly a rock or a hammer - and fell to the ground.

BBC: Rugby fan's warning after mugging

Its first action was just to hammer down briefly on a rock target last weekend - a simple check to prove the machinery was behaving as it should.

BBC: Curiosity Mars rover takes historic drill sample

Scientists need to be sure that when the big hammer tool turns in a rock it breaks the surface into a useable powder that will not clog or damage the sample handling mechanism.

BBC: Curiosity Mars rover deploys its rock brush

He said the drill diameter would be reduced from 28 inches to 26 inches until the hammer had cleared the hard rock but added that the slightly smaller diameter would not cause problems for the rescue.

CNN: STORY HIGHLIGHTS

Sponsors participate at every stage of the paleontological process, side-by-side with a site scientist: from the use of hammer and chisel to free fossils from hard rock, to the moulding of bone replicas for display at the on-site laboratory.

BBC: The dinosaur route of northwest Patagonia

Sougarret said the drill hammer had been swapped out but hit fresh problems after running into rock that was tougher than expected.

CNN: STORY HIGHLIGHTS