(left): Meridian Planum, Mars, scale about 50m (NASA Opportunity Rover); (right): Rock, dry river bed, Sunset Crater NP, AZ, scale about 200m (Stephen Strom)

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(left): Meridian Planum, Mars, scale about 50m (NASA Opportunity Rover); (right): Rock, dry river bed, Sunset Crater NP, AZ, scale about 200m (Stephen Strom)
(left): Meridian Planum, Mars, scale about 50m (NASA Opportunity Rover); (right): Rock, dry river bed, Sunset Crater NP, AZ, scale about 200m (Stephen Strom) ,  ​ ​ © © Stephen Strom,  Image courtesy Stephen Strom
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