Mars Pathfinder & Sojourner

On the morning of 4 July 1997, while Americans set out picnic blankets, a cocoon of airbags slammed into an ancient Martian flood plain, bounced at least fifteen times, the first rebounds reaching roughly fifteen metres, and rolled to a stop in Ares Vallis. Inside the deflating bags sat the first spacecraft to reach the surface of Mars in 21 years. At the Jet Propulsion Laboratory the room erupted when the signal reappeared. America was back on Mars, and it had arrived on Independence Day.

Pathfinder was NASA's wager that Mars could be done faster, better, cheaper. A Discovery-class mission costing roughly 265 million dollars including launch and operations, a fraction of Viking's price, it traded retro-rocket legs for parachutes and airbags and carried a passenger: Sojourner, a 10.6-kilogram rover the size of a microwave oven, named by twelve-year-old Valerie Ambroise for the abolitionist Sojourner Truth. A day after landing, Sojourner rolled down a ramp and became the first wheeled vehicle ever to drive on another planet.

The little rover crept among boulders nicknamed Barnacle Bill and Yogi, pressing its spectrometer against rocks swept there by catastrophic floods billions of years ago. Designed for seven days of roving, it worked for 83 sols, never straying more than about a dozen metres from the lander, which had been renamed the Carl Sagan Memorial Station for the astronomer who died months before touchdown. Together they returned more than 16,500 lander images, 550 rover images, and 15 chemical analyses before the lander fell silent on 27 September 1997.

Pathfinder was also the first planetary landing of the internet age. NASA's websites strained under hundreds of millions of hits in the first days as the world clicked through fresh Martian panoramas, a preview of how the public would experience exploration ever after. The mission's deeper legacy rolled on wheels: Spirit, Opportunity, Curiosity, and Perseverance all descend from the toy-sized rover that proved driving on Mars was possible.