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Rat Crumbs
Composite image of Adirondack with original dust coating, after RAT brushing, and after RAT excavation.
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Rat Crumbs

After three hours of "chewing" on sol 34, Spirit's RAT got its fill and scientists and engineers were left to marvel at the aftermath of its dusty meal - the momentous first unveiling of the secrets of a martian rock.

While the team was overwhelmed with the success of the operation, the apparent dark scarring around the RAT hole was perplexing.

"It looks like we took a blowtorch to Adirondack," joked Steve Gorevan, lead scientist for the rock abrasion tools on both rovers. "It's actually just the dust accumulation from drilling. However, we've never seen this kind of asymmetrical dust distribution when we used the RAT in testbeds on Earth. It could be that wind, which isn't a factor in a testbed, transported and spread the dust out."

After the RAT retreated, it was time for the other instruments to have a look at Adirondack's new dimple. The powerful alpha particle X-ray spectrometer (APXS) helped to reveal what could be a time-saving tip for the duration of the mission. The RAT used its brush to sweep the rock on the sol before drilling, in hopes of removing a coating of loose material whose composition could be different and misleading as to the composition of the rock itself. Since brushing is a time-consuming activity, scientists and engineers were pleased to see that it might be unnecessary in the future.

"The APXS tells the key story," Gorevan said. "The dust coating on these rocks doesn't really matter - it's not giving us false results. We didn't need to brush it away and we probably won't need to brush other rocks at the Gusev site, assuming the coating is as thin as Adirondack's."

Comparison of APXS data from before grinding and after grinding reveals that we are seeing less sulfur, potassium and chlorine than one would expect because the RAT has removed not only the dust but the first layer of rock. The reason the spectrometer is picking up any signs of the minerals is likely due to dust getting caught in the natural nooks and crannies of the rock, Gorevan noted.

The historic first grinding of a rock on Mars and the ongoing analysis could bring the team one step closer to tracing the history hidden in the rocks.

"We have established a ground-truth," Gorevan said. "For the first time ever in the history of Mars exploration we've gotten to look below the surface of any coatings or dust layers on martian rocks."

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