This undated handout two-picture combo of artist conceptions provided by NASA/JPL Caltech shows what NASA says are good candidates for a mission to capture an asteroid, haul it to the moon for ... more 
This undated handout two-picture combo of artist conceptions provided by NASA/JPL Caltech shows what NASA says are good candidates for a mission to capture an asteroid, haul it to the moon for astronauts to visit. One prime candidate swung close by Earth in 2011 so astronomers know its size, about 20 feet, mass and density, but they donât really know what it looks like. These images are two different artist conceptions of what the lightweight asteroid could look like, either a pile of small rocks flying together in formation, left, or a larger porous rock with pebbles surrounding it, right. (AP Photo/NASA/JPL Caltech) less 
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Associated Press | Photo By AP Photo/NASA/JPL Caltech
Fri, Jun 20, 2014 6:00 AM EDT