The Mars Exploration Rover mission is part of NASA's Mars Exploration Program, a long-term effort of robotic exploration of the red planet. Primary among the mission's scientific goals is to search for and characterize a wide range of rocks and soils that hold clues to past water activity on Mars.
This is important for several reasons.
1 For scientists to see if the planet is suitable for human life.
2 General planet discovery.
3 Atmosphere tests