A small roll for rover, a giant leap for mankind

As tiny titanium wheels churn the Martian soil, their tracks show space explorers the way to go. Charles Arthur reports

It might not seem that important: at 6.46BST yesterday morning an electric-powered car about the size of a microwave oven was halfway down a ramp; by 6.59 it was off it. But the cheers and roars from the 70 scientists greeting the news that "the rover is on the surface of Mars" were entirely in keeping with the occasion.

For this could be the future of successful, affordable space exploration. It could be the prototype of how we search for life in the solar system. The vehicle, called Sojourner, has already left its mark: a track from its six studded titanium wheels. Never before has a vehicle been driven on another planet. "Six wheels on the ground," reported flight director Chris Salvo as the signal came in. The response was ecstatic.

An hour after the vehicle moved off the ramp, the Sun went down and Sojourner was left parked overnight on the Martian soil, a symbol of our ability to build systems which can travel millions of miles and still stay in touch. Guided by lasers and feeding back stereoscopic pictures to a "driver" at mission control at the Jet Propulsion Laboratory (JPL) in Pasadena, California, it was waiting yesterday for the Sun to rise. The Martian day is 34 minutes longer than Earth's and is synchronised roughly with time on the West Coast of the US.

Scientists were preparing to explore the area around the Pathfinder rocket, using the rover's ability chemically to "sniff" rocks with its X-ray spectrometer and to examine the solidity of the soil by churning it with its wheels. Such examinations will go on for at least a week while the lander takes high-resolution photographs. Last night Sojourner was preparing to investigate a multi-coloured rock which has been dubbed "Barnacle Bill", because it appears to be covered with small markings. Then it will move to a larger rock, "Yogi". Even so, after the first two nights few of the 700 fingernails at JPL mission control will have survived unbitten. First there was the nerve-racking landing on Friday night, plummeting to the surface at 600mph. Then there was the three-hour wait to see if the lander had been damaged.

It turned out to be fine. But getting the rover off the lander proved troublesome. By Saturday morning the airbags which helped the lander survive impact had not deflated. That was overcome by lifting the "petals" of the lander up and down.

Then, more seriously, the computers on the rover and on the lander refused to talk to each other. Without that link, the solar-powered Sojourner could not be controlled from Earth, though it could have performed a two-day pre-programmed sequence of investigations.

Last night, after much anguish, the problem was solved, as are so many terrestrial computer problems, by turning the misbehaving components off and then on again. The controllers were relieved. "We feel like we've been invited back to the party," said rover operator Matt Wallace.

Scientists will use the rover's first few days on Mars to learn how to handle the vehicle. There is a time delay of almost 11 minutes before the signal reaches the "driver" on Earth from the vehicle on Mars.

So even though it moves at only 0.02 mph, about half an inch a second, the delay means that in the time it takes to see an event and to react to it, the rover will travel more than 53 feet. Thus the experience for the driver will be rather like trying to pick sites of interest while zipping along a motorway.

The significance of the Sojourner's little trundle lies in the possibilities it opens. Pathfinder is the first of a series of low-cost missions planned by the US space agency, Nasa. With a budget of only $266m (pounds 166m), it is a far cheaper method of exploration than putting people - who need food, water and air - into rockets."This really strengthens the case for unmanned missions," said Sir Martin Rees, Astronomer Royal.

But even the Martian adventure may pale beside planned expeditions to take samples from passing comets and even to dig beneath the surface of Europa, an icy moon of Jupiter, to look for signs of vestigial life.