NASA's Sample Return Challenge aims to make robots capable of navigating and retrieving samples by themselves. This image shows the space agency's past rovers (smallest to largest): Sojourner, Mars ... more 
NASA's Sample Return Challenge aims to make robots capable of navigating and retrieving samples by themselves. This image shows the space agency's past rovers (smallest to largest): Sojourner, Mars Exploration Rover and Curiosity. less 
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SPACE.com | Photo By NASA/JPL-Caltech
Mon, Jun 3, 2013 3:15 PM EDT