he successful launch Aug. 4 of NASA’s Mars Phoenix lander certainly is a noteworthy event, particularly given the history behind the mission, but a far more remarkable story has unfolded over the last three-and-a-half years on the surface of the red planet. There, two tiny NASA rovers are defying the elements and the odds while gathering data that is enhancing our understanding of Earth’s neighbor.

The Spirit and Opportunity rovers arrived separately at Mars back in January 2004, for what were supposed to be 90-day missions. That they have survived this long – both are in relatively good health – is nothing short of incredible. Even more amazing is that they have continued to hang on during the current flurry of dust storms that has blocked out much of the sunlight that the rovers need to recharge their batteries.

On July 20, NASA served notice that Spirit and Opportunity might not weather the

storm; two weeks later, with both rovers tantalizingly close to unexplored martian features that could bring exciting discoveries, scientists were still couching their situation as day to day. Spirit is in better shape at this point; it continues to make scientific observations, whereas Opportunity, which is suffering from lower power levels, is focused on staying alive.

But both already have far exceeded all expectations; anything they can do from here on out is that much more icing on the cake. The NASA-led team is to be congratulated.

The rovers also have given the Mars Phoenix lander a tough – perhaps impossible – act to follow. Interestingly, the timing of the missions could have been the other way around: Some of the Phoenix instrumentation and scientific objectives were inherited from the Mars Polar Lander, which was lost during its 1999 descent into the martian atmosphere; much of the Phoenix lander hardware was salvaged from the 2001 Mars Surveyor, which was canceled in the wake of that mishap. As it has turned out, Phoenix now has success rather than failure to build upon.