NASA are celebrating five years of success on Mars by two WALL-E style robots that were designed to last for an initial mission of just 90 days.

Intrepid rovers Spirit and Opportunity have been trundling about on opposite sides of the planet since they bounced to a landing, protected by giant airbags, in January 2004.

Amazingly, both survived a massive dust storm that blew up and encircled the planet in 2007, blotting out the sun and threatening to drain their solar power supplies.

Opportunity, which landed in the Meridiani Planum region of Mars, was already continuing to explore the martian surface on its six wheels despite nursing a broken robotic arm.

Spirit, in Gusev Crater, is in a more serious condition. After soldiering on for years with a broken right front wheel, it is conserving power to help keep it from dying.

Spirit’s wonky wheel turned out to be a lucky break. The rover was forced to drag it through the martian soil, creating a furrow that revealed salts and minerals that scientists realised must have been produced by flowing water.

Both rovers found deposits of sulphates and phosphates, which commonly form in water. Opportunity also spotted a crop of “blueberries” on a crater’s walls — not the fruit, of course, but mineral balls produced by water and left like a dirty ring around a bathtub.

The two rovers have phoned home a quarter of a million photos, driven more than 13 miles, climbed a mountain and descended into craters. An astonishing image of Opportunity, complete with tyre tracks on the edge of the spectacular Victoria Crater was taken from space.

Unlike WALL-E in last-year’s hit movie, the rovers cannot think for themselves. So a team of drivers take turns to steer them from Nasa’s Jet Propulsion Laboratory in California. WALL-E’s creators visited them at JPL for inspiration for designiing and animating their loveable little robot.

Each rover – about the size of a small car – has its own page set up by fans on Facebook which have been given the blessing of the Nasa chiefs. It is still not “rover and out” for the plucky duo. Nasa hopes to get more years of service out of both robots.

Team member Steve Squyres said: “The journeys have been motivated by science, but have led to something else important. This has turned into humanity’s first overland expedition on another planet.”

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