NASA's Mars Exploration Rover (MER) mission is an ongoing robotic space mission involving two Mars rovers, Spirit and Opportunity, exploring the planet Mars. It began in 2003 with the launch of the two rovers: MER-A Spirit and MER-B Opportunity -- to explore the Martian surface and geology; both landed on Mars at separate locations in January 2004. Both rovers far outlived their planned missions of 90 Martian solar days: MER-A Spirit was active until 2010, while MER-B Opportunity is still active in 2018, and holds the record for the longest distance driven by any off-Earth wheeled vehicle.

Based on this passage, what are the names of the two rovers currently exploring mars? Let's give stream of consciousness first:
The relevant information to answer the above question is: NASA's Mars Exploration Rover (MER) mission is an ongoing robotic space mission involving two Mars rovers, Spirit and Opportunity, exploring the planet Mars.
So, the final answer is Spirit.