NASA's Mars rover breaks off-Earth roving record

NASA's Opportunity Mars rover that landed on the Red Planet in 2004 now holds the off-Earth roving distance record after trekking for 40 km.

"Opportunity has driven farther than any other wheeled vehicle on another world," said John Callas, a project manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

The previous record was held by the Soviet Union's Lunokhod 2 rover.

"This is so remarkable considering Opportunity was intended to drive about one km and was never designed for distance. But what is really important is not how many kilometres the rover has racked up, but how much exploration and discovery we have accomplished over that distance," Callas added in a NASA statement.

The rover had driven more than 32 km before arriving at Endeavour Crater in 2011.

Here, it has examined outcrops on the crater's rim containing clay and sulfate-bearing minerals.

The sites are yielding evidence of ancient environments with less acidic water than those examined at Opportunity's landing site.

If the rover can continue to operate the distance of a marathon -- about 42.2 km - it will approach the next major investigation site mission scientists have dubbed "Marathon Valley".

Observations from spacecraft orbiting Mars suggest several clay minerals are exposed close together at this valley site, surrounded by steep slopes where the relationships among different layers may be evident.