Mars Exploration Rovers
Spirit and Opportunity
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Answer questions about the history of water on Mars.
Like Pathfinder and MSL, the Mars Exploration Rovers (MER) entered Mars's atmosphere directly from their interplanetary trajectories; they did not first orbit the planet the way Viking did.
After the airbag-protected landing craft settled onto the surface and opened, the rovers rolled out to take panoramic images, giving scientists information to select promising geological targets that tell part of the story of water in Mars's past.
The rovers visit(ed) locations to perform on-site scientific investigations on the surface of Mars. Opportunity is still operating today.
Cruise stage was spin-stabilized.
MER Project Website.