Quote:
Mars rover beams back striking photo of mystery spheres
Small spherical objects fill the field in this mosaic combining four images from the Microscopic Imager on NASA's Mars Exploration Rover Opportunity. The view covers an area about 2.4 inches (6 centimeters) across, at an outcrop called "Kirkwood" in the Cape York segment of the western rim of Endeavour Crater. The individual spherules are up to about one-eighth inch (3 millimeters) in diameter.
Although NASA’s new Curiosity rover is stealing all of the headlines, it’s the long-in-service Opportunity rover that’s snapped one of the most curious photos from the Red Planet.
The rover has encountered a series of spherical outcroppings on the rock that look different from the “blueberries” of iron-rich spherules it photographed when it landed in 2004.
“This is one of the most extraordinary pictures from the whole mission,” said Opportunity’s principal investigator, Steve Squyres of Cornell University in Ithaca, N.Y., on NASA’s website. “Kirkwood is chock full of a dense accumulation of these small spherical objects. Of course, we immediately thought of the blueberries, but this is something different. We never have seen such a dense accumulation of spherules in a rock outcrop on Mars.”
Source: http://news.nationalpost.com/2012/09...stery-spheres/
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On Earth these structures are formed in sedimentary rocks when minerals grow around a nucleation object. On Earth that object will often be a fossil, so sometimes there will be something interesting inside. Obviously I do not think these spherical objects are Martian fossils, particularly since they are only an eighth of an inch in diameter. However, the geological process is called "concretion."