"One way I like to think about it is that Opportunity is the field geologist doing the exploration type of stuff, and Curiosity is the geologist who then takes samples back to his lab to do more detailed analysis on them," planetary scientist Diana Blaney, with NASA's Jet Propulsion Laboratory in Pasadena, Calif., told Discovery News.
The different missions grew out of different, but complementary science goals.
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"When Spirit and Opportunity were built, we had places (on Mars) that we knew had had water, but we really didn't have any evidence for any place where water had been around doing chemistry on the surface for a long time.
"In that era the big questions were 'What is the history of water at these particular locations on Mars?'" Blaney said.
With its 10 science instruments and a two-year design life, Curiosity, which is about the size of a small car, is intended to address two difficult follow-on questions: whether Mars had ingredients besides water, such as organics, necessary for life and whether it had the means to preserve it.