The Spirit and Opportunity rovers together represented NASA's Mars Exploration Rover Mission (MER), part of the Mars Exploration Program. Launched about a month apart in 2003, the twin rovers’ main scientific objective was to search for a range of rocks and soil types and then look for clues for past water activity on Mars.
Curiosity is a car-sized Mars rover designed to explore the Gale crater on Mars as part of NASA's Mars Science Laboratory mission
Opportunity, also known as MER-B (Mars Exploration Rover – B) or MER-1 is a robotic rover that was active on Mars from 2004 until mid-2018.