This month marks the sixth anniversary of NASA's Spririt and Opportunity Mars robots. They were originally designed to explore Mars for about three months. But the two little robots have proven themselves to be survivors, lasting 6 Earth years (3.2 Martian years) in the severe Martian environment. Opportunity is still going strong but Spirit faces an uncertain future, trapped in "Troy", a sandy area on the sloping edge of Gusev Crater. NASA has been trying to get Spirit unstuck for some time without success. Spirit's right front wheel stopped working back in 2006 and now the right rear wheel has stopped working too. Dust is building up on Spirit's solar panels, reducing the exposure to declining sun light of Martian winter. According to rover power engineer Jennifer Herman,
At the current rate of dust accumulation, solar arrays at zero tilt would provide barely enough energy to run the survival heaters through the Mars winter solstice.
The best Spirit can hope for at this point is to survive winter but remain stuck, which will limit the science it can do. On the upside, Opportunity is going strong, taking photos such as the one above (shot on Sol 1798), and doing a lot of useful science too. Earlier in 2009, the US Congress passed a resolution recognizing the contributions to science that have been made by these two little robots.