This image provided by NASA shows long, narrow gullies along the walls of a crater on the giant asteroid Vesta taken by the NASA Dawn spacecraft. Scientists are unclear how these gullies formed and ... more 
This image provided by NASA shows long, narrow gullies along the walls of a crater on the giant asteroid Vesta taken by the NASA Dawn spacecraft. Scientists are unclear how these gullies formed and work is underway to determine their origin. (AP Photo/NASA) less 
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Associated Press | Photo By NASA
Thu, Dec 6, 2012 5:29 PM EST