On July 4, 1997, the Mars Pathfinder, encapsulated in a 17’ by 17’ tetrahedral airbag, bounced along the surface of Mars. Cocooned within the cushioning was a mobile robot the size of a microwave oven—Sojourner—the first rover to successfully operate on Mars. For 83 Mars days the Sojourner gathered critical information about the Martian environment, including the mineral composition of rocks and the topology near its landing site, which provided evidence that Mars once had water.