The US space agency's Mars rovers Spirit and Opportunity this month mark their fifth anniversary on the Red Planet, where they have endured harsh conditions and revealed a deluge of information.

The twin robots, which landed on Mars three weeks apart in January 2004, were initially expected to have just 90-day missions, but have since sent back to Earth a quarter-million images, toured mountains and craters and survived violent dust storms.

"The American taxpayer was told three months for each rover was the prime mission plan. The twins have worked almost 20 times that long," said NASA assistant administrator Ed Weiler in a statement.