"NASA rovers Spirit and Opportunity may still have big achievements ahead as they approach the fifth anniversaries of their memorable landings on Mars."

"Of the hundreds of engineers and scientists who cheered at NASA's Jet Propulsion Laboratory in Pasadena, Calif., on Jan. 3, 2004, when Spirit landed safely, and 21 days later when Opportunity followed suit, none predicted the team would still be operating both rovers in 2009."

"'The American taxpayer was told three months for each rover was the prime mission plan,' said Ed Weiler, associate administrator for NASA's Science Mission Directorate at NASA Headquarters in Washington. 'The twins have worked almost 20 times that long. That's an extraordinary return of investment in these challenging budgetary times.'"

NASA - Mars Exploration Rover Mission

"Surveying intact bedrock layers with the Compact Reconnaissance Imaging Spectrometer for Mars, or CRISM, scientists found carbonate minerals, indicating that Mars had neutral to alkaline water when the minerals formed at these locations more than 3.6 billion years ago. Carbonates, which on Earth include limestone and chalk, dissolve quickly in acid. Therefore, their survival until today on Mars challenges suggestions that an exclusively acidic environment later dominated the planet. Instead, it indicates that different types of watery environments existed. The greater the variety of wet environments, the greater the chances one or more of them may have supported life."

NASA - Scientists Find 'Missing' Mineral and Clues to Mars Mysteries

Spirit, mission designation MER-A (Mars Exploration Rover - A), is the first of the two rovers of NASA's Mars Exploration Rover Mission. It landed successfully on Mars on 04:35 Ground UTC on January 4, 2004, three weeks before its twin Opportunity (MER-B) landed on the other side of the planet. Its name was chosen through a NASA-sponsored student essay competition.

The rover completed its planned 90-sol mission, then, aided by cleaning events which resulted in higher power from its solar panels, went on to function effectively over twenty times longer than NASA planners expected. This allowed it to perform more extensive geological analysis of Martian rocks and planetary surface features. Initial scientific results from the first phase of the mission (roughly, the 90-sol prime mission) were published in a special issue of the journal Science.

On May 1, 2009, Spirit was stuck in soft soil on Mars, one of the mission's embedding events. NASA is carefully analyzing the situation to get the rover back on track, but it will take weeks before a new attempt will be made to extricate the rover from its current position called "Troy".

Source: http://en.wikipedia.org/wiki/Spirit_rover

Opportunity, mission designation MER-B (Mars Exploration Rover - B), is the second of the two rovers of NASA's Mars Exploration Rover Mission. It landed successfully at Meridiani Planum on Mars on January 25, 2004 05:05 Ground UTC (circa 13:15 local time), three weeks after its twin Spirit (MER-A) had landed on the other side of the planet. Its name was chosen through a NASA-sponsored student essay competition.

The NASA rover has continued to function effectively over twenty times longer than its planned 90-sol mission, aided by solar cell cleaning events, which allowed it continue performing extensive geological analysis of Martian rocks and planetary surface features.

Mission highlights include completion of the 90-sol mission, discovery of the first meteor on another planet, Heat Shield Rock (Meridiani Planum), and over 2 years studying Victoria crater. The rover narrowly survived dust-storms in 2007, and is now making its way to Endeavour crater.

Source: http://en.wikipedia.org/wiki/Opportunity_rover