Mars Pathfinder & Sojourner

Mars Pathfinder proved that NASA could land on Mars cheaply, quickly, and with a radically new approach — and it delivered the first wheeled rover to another planet. Launched in December 1996, the mission reached Mars on July 4, 1997, using an audacious landing system: instead of the complex retro-rockets of the Viking era, Pathfinder was cocooned in airbags and simply bounced across the surface until it rolled to a stop.

The lander carried a small rover named Sojourner, about the size of a microwave oven, which became the first mobile robot to explore the surface of Mars. Over the following weeks, Sojourner trundled between nearby rocks — nicknamed by the team with playful names — analyzing their composition with an onboard instrument. It demonstrated that a rover could navigate the Martian terrain and make decisions with limited human guidance across the long communication delay, laying the groundwork for the far more capable rovers to come.

Pathfinder was also a public phenomenon. Its images and daily updates drew record traffic to NASA's early websites, bringing Mars exploration to a global audience in a way no previous mission had. The rock-strewn landing site showed evidence of ancient catastrophic floods, reinforcing the growing picture of a Mars that was once far wetter than today. The mission's low cost and high impact reshaped how NASA approached planetary exploration, and Sojourner's tracks were the first ever made by a rover on another world — a direct ancestor of Spirit, Opportunity, and Curiosity.