Radio signals instructing Spirit to make its first brief excursion were sent by mission controllers at the Pasadena-based Jet Propulsion Laboratory at 12:21am PST (3:21am EST/0821 GMT), but they said it would take at least 90 minutes to confirm through a return transmission the rover had moved. 

The golf cart-sized probe was expected to crawl only about 10 feet in its initial outing, a 78-second prelude to its mobile search for signs of life-sustaining water.

For at least the next 78 days, Spirit is supposed to roam its surroundings in Gusev Crater, a barren, wind-swept basin about the size of Connecticut that scientists believe may have been the site of an ancient lake bed once fed by a long, deep martian river. 

Spirit already has sent back stunning, three-dimensional, colour photographs of Mars, revealing the planet's terrain in vivid, unprecedented detail. The JPL team is even more eager to closely examine soil and rocks, using a collection of high-tech geologic gadgets carried on the rover's robot arm. 

New era of exploration

The command for Spirit's first jaunt, away from the landing pod in which it bounced to the Martian surface on 3 January, comes as NASA looks forward to a new era of manned space exploration called for on Wednesday by President George  Bush, including the eventual goal of sending astronauts to the red planet.

Spirit is the fourth probe ever to successfully land on Mars, following in the footsteps of two Viking landers in the 1970s and the Pathfinder mission in 1997. 

On 24 January, Spirit's twin rover, named Opportunity, is scheduled to land on the opposite side of the planet for its own three-month mission.

Later on Thursday, JPL controllers plan to aim an instrument called a mini-thermal emission spectrometre, or mini-TES, upward to obtain a reading of infrared radiation emitted by particles in the martian sky at the time the European obiter Mars Express snaps the same type of images from 186 miles overhead. 

The simultaneous images of the martian sky from opposite vantage points will provide scientists with new detailed data about the composition of the planet's atmosphere, deputy project scientist Albert Haldemann said.