Every time Spirit has gained altitude, we've found different rock types,
Spirit is our tough, hardworking robot. Opportunity looks like she just came off the showroom floor, clean and pretty.
Spirit has given us a wonderful window into the very ancient past of Mars. It was a violent place, a place where meteorite impacts, volcanic explosions happened frequently, where hot stuff was raining from the sky.
This climb was motivated by science. Every time Spirit has gained altitude, we've found different rock types. Also, we're doing what any field geologist would do in an area like this: climbing to a good vantage point for plotting a route.
What field geologists typically do - and Spirit is a robotic field geologist - is you climb to the top of the nearest hill and take a look around so you get the lay of the land and figure out where you want to go,