Nasa's engineers cheered this weekend when images returned from Mars showed the six-wheeled geological research vehicle was finally freed from the dune and making tracks, according to a posting on the JPL website (www.jpl.nasa.gov).

Engineers worked for nearly five weeks to manoeuvre the craft out of the dune.

A photograph on the JPL site on Sunday showed fresh rover tracks stretching across what appeared to be the surface of a large dune.

Parallel missions

The red planet is the subject of
several robotic explorations

Opportunity and its twin robotic explorer, Spirit, are 16 months into their mission and have been traversing opposite sides of the red planet since landing there in January 2004.

Early in the mission, Opportunity found layered bedrock bearing geological evidence of a shallow ancient sea. More than a year later, Spirit found layered bedrock after driving more than two miles and climbing into a series of hills.

Opportunity got its wheels stuck on 26 April while trying to cross the soft sand of the Meridiani Planum, a ripple-shaped
dune of windblown dust and sand.