Mars rover Curiosity driving backwards

NASA rover Curiosity is now being driven in reverse mode on Mars to protect its wheels.

The rover drove 100.3-metre backwards, the longest one-day trek in more than three months, said NASA.

Rover operators were practising driving in reverse after ground tests showed that it might better protect the rover's wheels as it travels over sharp rocks.

Curiosity hit some unexpectedly rough terrain en route to Mount Sharp, a five kilometer mound of layered sediment in the middle of Gale Crater, where the rover landed 18 months ago.

Scientists are eager to reach the mountain's foothills to look for habitats that could have supported microbial life and preserved the evidence.

"We wanted to have backwards driving in our validated toolkit because there will be parts of our route that will be more challenging," Curiosity project manager Jim Erickson said in a statement.

In addition to driving Curiosity in reverse, operators used pictures taken by orbiting Mars spacecraft to plot a course to Mount Sharp that seems to transverse smoother ground.

Scientists plan to stop at a waypoint called 'Kimberley' where different types of rock layers intersect.

"No route will be perfect; we need to figure out the best of the imperfect ones," Erickson said.