NASA says it might need to choose a different route for its Mars rover Curiosity as the 1-ton vehicle makes it way to its next destination, the base of a high mountain on the Red Planet.

Its intended path to Mount Sharp, the 3.4-mile-high peak in the middle of the rover's Gale Crater landing site, was to be through a sandy, football field-size patch of ground that controllers dubbed "Hidden Valley."

However, those controllers had Curiosity turn back after entering the northeastern end of the valley when the going got surprisingly slippery, the space agency announced.

Wheel slippage in the loose sand proved to be considerably worse than predicted based on a test rover's drive on sand dunes in the California desert, NASA's Jet Propulsion Laboratory in Pasadena, Calif., said.

"We need to gain a better understanding of the interaction between the wheels and Martian sand ripples, and Hidden Valley is not a good location for experimenting," said Jim Erickson, Curiosity Project Manager.

If the rover is sent back into Hidden Valley there is no alternate exit from it except at its far end, so the science team says it is looking at possible alternative paths that would see Curiosity skirting the valley to the north.

If and when the rover reaches Mount Sharp, it will be sent on a climb though its foothills in an effort to assess from the rocks it encounters a history of the Red Planet's evolution from a wet and warm planet to the dry, cold world it has become.

It's all a part of the primary aim of the $2.5 billion mission that put Curiosity on the planet's surface, to determine if Mars could ever have sustained microbial life.

Curiosity has already confirmed that ancient Mars had systems of streams and lakes that may have offered habitats amenable to life.

The rover has covered 5 miles on the Martian surface to this point, and has around 2 miles to go to reach the foothills of Mount Sharp, a goal NASA is hoping can be accomplished by the final days of this year.

In traversing more rocky terrain in its travels to this point, Curiosity has suffered damage to its wheels from sharp rocks tearing holes in them.

That was one reason NASA chose to investigate a route to Mount Sharp through softer, sandy terrain, a decision that has brought its own problems and led to the rover being backed out of Hidden Valley and taken a viewpoint to examine possible alternative routes.