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Curiosity's first sample from mountain matches orbital observation

Jenny Winder, News Writer
Nov 7, 2014, 19:01 UTC

Sen—The first hole drilled into a martian mountain by NASA's Curiosity rover has yielded the mission's first confirmation of a mineral that had been mapped from orbit. The sample of reddish rock powder taken shows oxidation that could have provided a chemical energy source for any microbes.

Curiosity collected the powder by drilling into a rock outcrop at the base of Mount Sharp in late September and delivered a pinch of the sample to the Chemistry and Mineralogy (CheMin) instrument inside the rover. The sample, from a target called Confidence Hills within the Pahrump Hills outcrop, contained much more hematite than any rock or soil sample previously analyzed by the rover.

Hematite is an iron-oxide mineral that gives clues about ancient environmental conditions from when it formed. In observations reported in 2010, before selection of Curiosity's landing site, a mineral-mapping instrument on NASA's Mars Reconnaissance Orbiter provided evidence of hematite in the geological area that includes the Pahrump Hills outcrop.

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This side-by-side comparison shows the X-ray diffraction patterns of two different samples collected from rocks on Mars by NASA's Curiosity rover. Image credit: NASA/JPL-Caltech

The landing site is inside Gale Crater, an impact basin about 96 miles (154 kilometres) in diameter with Mount Sharp rising about three miles (five kilometres) high in the centre.

"This connects us with the mineral identifications from orbit, which can now help guide our investigations as we climb the slope and test hypotheses derived from the orbital mapping," said Curiosity Project Scientist John Grotzinger, of the California Institute of Technology.

Ralph Milliken of Brown University, a member of Curiosity's science team and lead author of the 2010 report, said, "We're now on a path where the orbital data can help us predict what minerals we'll find and make good choices about where to drill."

The form of hematite at Pahrump Hills is most important as a clue about oxidation conditions. Plenty of other evidence in Gale Crater has testified to the ancient presence of water.

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This view shows the path and some key places in a survey of the Pahrump Hills outcrop by NASA's Curiosity Mars rover in autumn of 2014. Image Credit: NASA/JPL-Caltech/MSSS

Curiosity has already investigated a low area of Gale Crater called Yellowknife Bay. Rocks there held evidence of wet environmental conditions billions of years ago that offered ingredients and an energy source favorable for microbial life.

The rover then traveled to the base of Mount Sharp. The hematite found in the first sample from the mountain shows environmental conditions different from those recorded at Yellowknife Bay. The rock material had interacted with water and atmosphere to become more oxidized. 

The rocks analyzed earlier also contain iron-oxide minerals, mostly magnetite. One way to form hematite is to put magnetite in oxidizing conditions. The latest sample has about eight per cent hematite and four per cent magnetite. The drilled rocks at Yellowknife Bay and on the way to Mount Sharp contain at most about one per cent hematite and much higher amounts of magnetite.

The sample is only partially oxidized, and preservation of magnetite and olivine indicates a gradient of oxidation levels that could have provided a chemical energy source for microbes.

The rover team is now using Curiosity to survey the outcrop and assess possible targets for close inspection and drilling.

Curiosity will eventually proceed farther up Mount Sharp, where higher layers include an erosion-resistant band of rock with such a strong orbital signature of hematite. The feature is known as Hematite Ridge.