The story of the two robot vehicles, Spirit and Opportunity, that were sent to explore Mars, lasting far past their projected lives of three months and sending back invaluable images of the environmentally hostile planet. Interest Level: 3-6 Reading Level: 6.4 ATOS Book Level: 6.4 AR Interest Level: MG AR Points: 3 AR Quiz: 151231EN Reading Counts Level: 7.4 Reading Counts Points: 7 Lexile Measure: 950 Guided Reading Level: X.