Eight months after landing on Mars, the rovers Spirit and Opportunity still keep Steve Squyres busy. Each robot has more than doubled its expected lifetime of 90 sols, or Mars days, but the pace continues to be hectic as the team at NASA’s Jet Propulsion Laboratory tries to squeeze even more work out of the plucky pair. Between normal flight-operations meetings and a conference about a possible dune drive for Opportunity, Squyres, the head of science operations for both rovers, managed to wolf down some lunch while he spoke with me about the rovers’ successes and future plans.
The highlight of the mission so far remains Opportunity’s discovery of strong evidence for ancient water in the Meridiani Planum region. Considering the size of Mars—its surface is as extensive as all of Earth’s continents combined—finding the critical evidence so close to Opportunity’s landing site was a stroke of good fortune, Squyres says. Proof for water came from a series of discoveries. Opportunity found high concentrations of sulfate minerals and other rocks containing holes with shapes showing that sulfate minerals were once present. The probe also detected concentrations of chlorine and bromine in the rocks that are consistent with rocks formed by evaporation on Earth and discovered striking “blueberries,” concretions of hematite, a water-related mineral. More evidence came in the form of an iron sulfate mineral, jarosite, known to form on Earth in acidic groundwater. The presence of jarosite at Meridiani Planum means that a shallow caustic sea once covered this area. In the months since the big find, Opportunity has conducted follow-up examinations of nearby layered rocks. “The fundamental story of rocks that were laid down in liquid water and that are rich in sulfate salts has remained the same as we have worked our way down through this stack of layered sediments,” Squyres says.
Complementing the data from the rovers, the Mars Global Surveyor orbiting the Red Planet has examined the Meridiani region from a greater distance. On September 9 Brian Hynek of the University of Colorado reported that the patterns of hematite show that a sea of a similar area to Europe’s Baltic Sea once covered this area of Mars.
On the opposite side of the Red Planet, meanwhile, Spirit continues to explore Gusev Crater. So far, the rover has traveled almost two and a half miles, more than twice as far as Opportunity. In June Spirit found a softball-size rock studded with bulb-shaped spokes in the crater’s Columbia Hills. The rock, dubbed “pot of gold” by the NASA team, also contains hematite. Hematite is more difficult to interpret than jarosite, however, because it can sometimes form even where there is little water present. Squyres and his science team are still trying to determine how much water really was present in the crater and what forces could have eroded the rock’s strange spokes, which have never been seen on rocks here on Earth.
Now just a few weeks away from the height of the Martian winter, Squyres and his team are managing a new challenge: Maintaining the solar-powered rovers in working order as the days grow shorter and sunlight becomes scarce. The team is keeping the rovers on slopes that face north to maximize sunlight. Although they receive less power than before, the trickle should keep key electrical systems running, as long as no critical components fail. The rovers’ mechanical systems seem to be holding up well, Squyres reports, although ground controllers recently had to adjust how Spirit drives to minimize wear on its right front wheel. Even if no systems fail, dust buildup on the rovers’ solar arrays will gradually cause power failure and bring the mission to an end.
The length of the rovers’ mission is leading to one unexpected result: fatigue among the science crew. “I’m exhausted. The whole team’s exhausted,” Squyres says. “These rovers—they just don’t quit.” He is cautiously optimistic that the rovers will survive the Martian winter and continue exploration in the spring. If they do, he’s confident that NASA will scrounge up funding to keep the mission going for as long as the rovers can soldier on. “Mars is a big planet—so big that a rover’s work is never really done,” he says. “The hard part is choosing wisely among the enormous number of things that we have to do.”