Mars Opportunity 'keeps on tickin'

Washington: The Mars Rover Opportunity has arrived at the rim of a big crater that scientists never thought it could reach, NASA said.

Geologists controlling the golf-cart-sized robot hope it can explore the depths of Victoria Crater to find out more about the history of the red planet - especially whether water still exists there.

So far it has taken pictures of rugged walls with layers of exposed rock and a floor blanketed with dunes, the US space agency said.

''This is a geologist's dream come true,'' said Steve Squyres of Cornell University in New York on Wednesday, the principal investigator for NASA's twin rovers Opportunity and Spirit.

''Those layers of rock, if we can get to them, will tell us new stories about the environmental conditions long ago. We especially want to learn whether the wet era that we found recorded in the rocks closer to the landing site extended farther back in time,'' he said.

Opportunity has lasted 10 times as long as the 90 days NASA originally projected. It has been exploring Mars since January of 2004 and driven more than 9 kilometre.

''We're so proud of Opportunity, the rover that 'takes a lickin' but keeps on tickin','' said a Mars rover mission manager at NASA's Jet Propulsion Laboratory in California, Cindy Oda.

''It continues to overcome all challenges despite its aging parts and difficult terrain,'' she said.

Spirit, the other rover, is hibernating through winter on the other side of Mars.