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The Mars rover Opportunity has taken the first close-up pictures ever of Martian bedrock, and these reveal important new details of the intriguing strata. The rover's earlier observations revealed layering, as well as round grains in the soil, both highly suggestive of sedimentary rocks deposited in water.
The new close-up images show that the thinness of the parallel layers of the rock continues down to the smallest scales the images are capable of showing. Furthermore, the small bead-like spheres seen earlier on the soil turn out to be heavily concentrated in the bedrock itself.
The spheres are both "in the soil and in the outcrop", said Jim Erickson, Opportunity mission manager, on Sunday. An earlier microscope image showed the spheres ranged up to three millimetres in diameter, and those seen in the new images appear similar.
Earlier in the mission, some team members had suggested that if rounded grains were found in the layered rock, that would strongly imply a sedimentary formation process in deep water subject to wave action. On Earth, waves can produce very smoothly rounded grains, which can then be buried and compressed into rock.
Concentric rings
However, a volcanic mechanism could also account for both the fine layering and the grains, with eruptions of ash alternating with eruptions of molten rock whose droplets hardened to form glassy spheres. But the absence of any known volcano in the region seems to make this less likely. Another possibility is sedimentary formation, but caused by wind, not water.
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