Mars rover update
New evidence for water in Mars's past and more discoveries of intriguing rocks mark the twin rovers' extended missions so far.
August 18, 2004; updated August 19
Mission scientists report that while the twin Mars rovers, Spirit and Opportunity, are starting to show some wear and tear after weathering more than 8 months on the Red Planet, they continue to return exciting data to Earth. The initial 3-month mission for each rover was completed successfully in April, and the extended missions are a boon that investigators hope will last through the martian winter.
Spirit, plagued by a bum wheel, has been driving on five of its six wheels except on the most difficult terrain. Having traveled more than 3 kilometers from its landing site, Spirit currently is positioned at an outcrop named Clovis inside the Columbia Hills. Preliminary images and data indicate the area contains rocks that were altered by water sometime in Mars's past.
Compared to basalt from within the crater, Clovis contains a greater concentration of water-soluble elements, including sulfur, chlorine, and bromine. "This is the most compelling — most powerful — evidence [for water] that we have seen in the rocks at Gusev," said Steve Squyres of Cornell University and principal investigator for the science instruments on both rovers. "So far, we have intriguing clues hinting that this rock Clovis has interacted with liquid water. We still need to understand the nature of that interaction."
At Meridiani Planum, Opportunity has been driving carefully into Endurance Crater. During its descent, the rover took detailed measurements of progressively older rocks in the stratigraphy. The samples showed that while the amount of sulfur and magnesium in the rocks declines slightly, the amount of chlorine present rises dramatically. While the samples indicate the rocks have basically the same general chemistry, the layers probably were deposited there under different conditions.
Also deep in the crater, at Axel Heiberg outcrop, scientists are investigating what appear to be variations of the now-familiar "blueberry." Red instead of blue-gray and coarse instead of smooth, the newly identified "popcorn" rocks also vary in size unlike the blueberries. In some cases, spherules contain a mixture of both red and blue particles. While a number of hypotheses have been suggested, the exact origin of these concretions remains a mystery. Says Zoe Learner, a science team collaborator from Cornell, "even though we've driven away [from the area], we're definitely going to look at this data a lot more carefully."
So while scientists continue to puzzle over new data and piece together Mars's history, the rovers ramble on. After it concludes its investigation of Clovis, Spirit will be headed uphill toward some layered bedrock. Opportunity may linger at the base of Endurance crater to probe the edge of a dune field, but only if mission planners deem it safe. The rover also will investigate a very unusual-looking, lumpy rock on its way out. If the solar-powered batteries on each rover can withstand progressively lower Sun angles as winter advances on Mars, we can expect more exciting discoveries — and questions — to come.