Curiosity is building towards using its hammer-drill, the last major tool yet to be deployed on the mission.

BBC: Curiosity Mars rover deploys its rock brush

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

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