Curiosity isn’t the first Mars rover, of course. The first was the small rover Pathfinder, which spent nearly three months on Mars in 1997 and set the precedent for all following rovers. Most people are probably more familiar with the Mars Exploration Rovers (MER), Spirit and Opportunity. The MER twins landed on opposite sides of Mars in 2004, their mission to answer the big question: has there ever been permanent water on Mars? In the time since their deployment, these rovers, along with the handful of other landers and orbiters we’ve sent to Mars, have uncovered astounding evidence of past Martian environments: geologic features that hint at ancient river beds, floods, and perhaps even oceans. The resounding answer is yes, Mars used to have plenty of water.
And why do we care if Mars had water? Because on Earth, water is the basis of all life. If Mars had water at one point, could it also have had life like we have on Earth? This is the underlying question in all Mars research, and it is the main objective of the Mars Science Laboratory mission.