1997: Sojourner rolls onto the surface of Mars

On 6 July 1997, two days after NASA's Mars Pathfinder mission touched down in the dusty plain of Ares Vallis, a microwave-oven-sized rover named Sojourner rolled down a folding ramp and pressed its six wheels into Martian soil. It was the first wheeled robot to operate on another planet, and its short, careful drive marked a quiet but genuine milestone in the history of robotics and autonomous systems.

Sojourner was tiny by today's standards: about 65 centimetres long, powered by a modest solar panel, and controlled by an 8-bit, 16-megahertz processor with roughly 512 kilobytes of memory — far less computing power than a modern calculator watch. Yet it had to solve a problem no earthbound robot faced at the time. Radio signals between Earth and Mars take several minutes to travel each way, far too slow for a human operator to steer the rover in real time or react to a sudden obstacle. Engineers at NASA's Jet Propulsion Laboratory gave Sojourner a simple but effective form of onboard autonomy: a hazard-avoidance system that used light stripe cameras to detect rocks and slopes, letting the rover pause, assess, and choose its own safe path before continuing along a route sketched out by human planners.

This was not artificial intelligence in the sense of learning from data or holding conversations, but it was a working example of a machine making independent, moment-to-moment decisions in an unpredictable environment, based on rules its designers had anticipated in advance. Over 83 days of operation, Sojourner travelled only about 100 metres in total, yet it proved that semi-autonomous robots could be trusted to explore hostile terrain without constant human hand-holding.

The mission's success helped justify decades of increasingly ambitious successors: Spirit and Opportunity in 2004, Curiosity in 2012, and Perseverance in 2021, which now carries the small autonomous helicopter Ingenuity and uses far more sophisticated computer-vision and path-planning software to navigate for itself across kilometres of Martian landscape.

Sojourner's cautious roll onto red dirt is a useful reminder that today's headline-grabbing AI, from chatbots to self-driving cars, sits atop a much older and less glamorous engineering tradition: giving machines just enough judgement to act sensibly when no one can tell them what to do next.