Mars exploration has been dogged by disasters. Of 31 robotic missions to the red planet only 11 have been completely successful. After six initial failures, the fly-by in 1964 by the Mariner 4 spacecraft paved the way, but the first major success was the one-billion dollar Viking 1 and 2 landers and orbiters. The first lander touched down on the western slopes of Chryse Planitia (the Plain of Gold) in August 1975 and the second in Utopia Planitia of the other side of Mars, close to the edge of the north polar cap, in September 1975. Both were searching for water and life. Their cameras revealed a gently rolling freeze-dried ferric-oxide-red wasteland, with wind-blown fine dust drifting into impact craters and clinging to eroded rocks, all shivering beneath a thin carbon dioxide atmosphere. The Martian surface was blasted by cosmic radiation because Mars has only a negligible magnetic field which is incapable of shielding the planet from incoming ionised particles. It was also illuminated by life-threatening doses of ultraviolet light. The Martian soil was apparently antiseptic and organics-free and was rich in peroxides and superoxides. Cameras on board the Viking probes enabled scientists on Earth to select specific soil samples from the surroundings. These were then collected by manipulating scoops and sucked into miniature onboard biology laboratories. There the soil was exposed to water, and liquid food laced with radioactive carbon. The results indicated that the planet Mars was lifeless.

Observations of the surrounding landscape continued for six years. Little changed. The banks of wind-blown Martian dust seemed to be much more permanent than Earth’s sand dunes. What was really exciting, however, was the simple fact the Earth-made Viking probes were out there, on the surface of a neighbouring planet, standing on the soil and observing features in millimetre detail, whilst around them the wind roared, and the dust hissed, and occasion rumbles from nearby landslides and active volcanoes rent the thin poisonous air.

On 4 July 1997 Mars Pathfinder, a $250 million, ‘faster, better, cheaper’ mission, landed close to the mouth of a canyon, Ares Vallis, that some 3.6 to 4.5 billion years previously had been carved out by a flash flood of water. A new epoch of Mars exploration was launched. Mars Pathfinder was carrying with it Sojourner, a small, 10.6 kg, half a meter long, six-wheeled roving robot. This could be guided from Earth, rather like a child can guide a radio–controlled toy car. Sojourner, moved away from Pathfinder at about 0.6 metre per minute and eventually examined 250 square meters of the nearby soil and rocks. Surprisingly there was little evidence of chemical diversity. The rocks were volcanic and consisted of a mixture of basalt and quartz, very similar to the Andes Mountains in South America.

Sojourner added much excitement and drama to the mission, and showed that a Martian rover could be effectively driven and manipulated from Earth. This remote robotic rover could explore the nearby planetary surface effectively, quickly and relatively cheaply. It could steer round or climb over rocks, and maintain a steady course. If it fell over, however, there was nobody around to put it back on its wheels again.