... Shadow of a Martian Robot . ... Credit Copyright: Mars Exploration Rover Mission , JPL , NASA Explanation: What if you saw your shadow on Mars and it wasn't human ? Then you might be the Opportunity rover currently exploring Mars. Opportunity and sister robot Spirit have been probing the red planet since early 2004, finding evidence of ancient water , and sending breathtaking images across the inner Solar System . ... 2003 2004 . ... Publications with keywords: Mars - Opportunity rover . ...