Those plucky little NASA rovers! The robotic pair landed on opposite sides of the planet in January 2004, and have far exceeded their expected lifespans of 3 months. Instead, over 4 years later, Spirit and Opportunity are still trucking over the terrain, snapping photos like tourists and digging trenches in the dirt.
The crafts that held the rovers were cocooned in airbags during their landings, which allowed them to bounce and roll over the surface. Once the rovers rolled out, they began exploring craters and hillsides, and eventually discovered gullies that may have been carved by liquid water during a warmer era of Martian history.