Curiosity Function defines Form

NASA’s Mars Exploration Rover (MER) mission is an ongoing robotic space mission involving two Mars rovers, Spirit[1] and Opportunity,[2] exploring the planet Mars. It began in 2003 with the sending of the two rovers: MER-A Spirit and MER-B Opportunity—to explore the Martian surface and geology. Both rovers outlived their planned missions of 90 Martian solar days by far. MER-A Spirit was active until 2010. MER-B Opportunity is still active. The success of the two MERs led to the Mars Science Laboratory (MSL) mission, sending a bigger rover Curiosity in 2012.
[Source: https://en.wikipedia.org/wiki/Mars_Exploration_Rover]