NASA's twin robot geologists Spirit and Opportunity, known collectively as the Mars Rovers, celebrated five years on the planet's surface in January of 2009. The two rovers, who are identical twins of each other, continue to provide scientists with thousands of images and geological samples of the red planet.CNN: NASA's rovers mark five years on Red Planet (January 3, 2009)

1. June, 2003: Rovers are launched
2. January 3, 2004: Spirit lands on Mars
3. January 25, 2004: Opportunity lands on Mars
4. June 28, 2007: Opportunity descended a 200-foot-deep crater to search for ancient signs of water
5. March, 2008: Threats of budget cuts to the program quickly reversed
6. November, 2008: Spirit's status listed as "Serious but Stable" to do lack of solar chargingMars Rovers: Spirit
7. November, 2008: Opportunity began a 2-week independent exploration of "Santorini" areaMars Rovers: Opportunity

Spirit and Opportunity are dependent on their solar arrays to maintain power and functions during their missions. Solar power is used to move the crafts, to run the several analytical tools and to heat components so they do not freeze during the long Martian winters. It was originally thought that the probes would only be able to survive three months on the surface as martian dust accumulated on the solar chargers and prevented recharging. However, dust storms on the surface of mars helped to blow dust off of the arrays and have allowed Spirit and Opportunity to last far beyond their initial mission.FOX News: Mars Rover Meant for 3-Month Mission Still on the Job 5 Years Later (January 4, 2009)

The rovers also survived threats of budget cuts in 2008. The funding for the missions was threatened to be cut in March, 2008, which may have scarified one or both rovers. However, less than 24 hours later, the edict was quickly reversed. Nevertheless, the extended mission length of the rovers which included millions of dollars in unexpected costs, may affect future plans and missions to mars.Universe Today: NASA U-Turn Over Mars Rover Funding (March 25, 2008) FOX News: Cost Overruns Threaten NASA's Mars Rover Project (October 8, 2008)

1. Determine whether Life ever arose on MarsMars Exploration Rover Mission: Goals
2. Characterize the Climate of MarsMars Exploration Rover Mission: Goals
3. Characterize the Geology of MarsMars Exploration Rover Mission: Goals
4. Prepare for Human ExplorationMars Exploration Rover Mission: Goals