Which NASA mission sent the twin rovers Spirit and Opportunity to Mars?

NASA’s Mars Exploration Rover mission sent the twin rovers Spirit and Opportunity to Mars. The two spacecraft were designed as robotic geologists to study Martian rocks and soils for evidence of ancient water and environmental conditions.

Spirit, designated MER-A, launched on June 10, 2003, while Opportunity, or MER-B, launched on July 7, 2003. Both reached Mars in January 2004, landing at widely separated sites: Spirit in Gusev Crater and Opportunity in Meridiani Planum.

The rovers were planned for roughly 90 Martian sols, but both greatly exceeded that goal. Spirit operated until 2010 after becoming stuck, while Opportunity continued working until 2018, when a planet-wide dust storm blocked sunlight from its solar panels. Their observations supplied strong evidence that liquid water had once shaped parts of Mars.

Mars Pathfinder is a different mission, famous for delivering the Sojourner rover in 1997. Mars Science Laboratory carried Curiosity, and Mars 2020 carried Perseverance; neither launched Spirit and Opportunity.