Happy Birthday Spirit!
It's been an amazing five years since your thrilling plunge through the thin Martian atmosphere, bouncing to a stop in Gusev Crater. Lasting twenty times longer than your principal 90-sol mission, you've really put the "exploration" into Mars Exploration Rover!
Spirit has a long list of accomplishments and discoveries including signs of a watery Martian past and a former environment suitable for microbial life. Spirit, and its twin Opportunity have, as reported by CNN:
...returned 250,000 images, covered more than 21 kilometers (13 miles), climbed a mountain, descended into craters, struggled with sand traps and ageing hardware and survived dust storms, NASA said.
Steve Squyres, a principal investigator on the Spirit MER project noted that this is truly humanity's first overland exploration of another planet:
"When people look back on this period of Mars exploration decades from now, Spirit and Opportunity may be considered most significant not for the science they accomplished but for the first time we truly went exploring across the surface of Mars."
Lest readers think all is fun and games for you on Mars, the photo below shows that exploring Mars really is a Dirty Job. Where's Mike Rowe when a rover needs him?