Let me tell you what! NASA has sure gotten their money's worth with those two little rovers that they sent to Mars. Both rovers are still on the go and still making valuable contributions to our scientific knowledge.
Initially their mission was slated to last only 90 days. As that estimation came and went both were still going strong. Then there was the first Martian winter. Scientists speculated that the pair of rovers could not collect enough sun light to survive through the winter... Again the rovers defied the naysayers. They were dropped on the surface of Mars in April of 2004 and while they are starting to show their age, both are continuing to explore the surface of Mars and push forward the limits of our understanding. This is the kind of value I like to see from an investment of tax payer money.
Recently NASA scientists discovered yet another indication that Mars was once awash with water. The discovery occurred largely through serendipity. Spirit, the rover dropped on the rugged Gusev Crater has been having trouble with its right front wheel. Because of that, it drags the wheel along where ever it goes, churning up the soil as it moves. In the picture above you see a light batch of sand uncovered by the frozen wheel's passing. This light soil interested the rover's NASA handlers so they maneuvered the rover back around so that it could lower its alpha particle X-ray spectrometer on the soil and analyze the soil's composition. It turns out that the soil is 90% pure silica, a mineral that can only form in the presence of liquid water.
I've kept my eye on the science being returned by these rovers since the beginning and I'm very happy to see that they are still alive and kicking!