Mars Exploration Rover

Spirit and Opportunity, MER-A / B, MER-1 / 2

Mission Profile

Mars Exploration Rover (MER) comprised twin NASA rovers Spirit (MER-A) and Opportunity (MER-B), launched on Delta II 7925-9.5 rockets in June 2003 and landing in January 2004 at Gusev Crater and Meridiani Planum respectively. Designed for 90-day missions, both rovers far exceeded their planned lifetimes: Spirit operated for over six years until becoming stuck in soft soil in 2009 and going silent in 2010, while Opportunity drove for nearly 15 years and 45.16 km — the all-time distance record for any off-Earth rover — before a planetary dust storm ended its mission in June 2018. Opportunity's most significant discovery was evidence that Mars once had standing liquid water in an environment potentially suitable for microbial life, finding layered rocks in which water-soluble minerals had precipitated from shallow liquid water. Together Spirit and Opportunity conducted the most successful Mars surface missions before Curiosity and Perseverance, transforming the scientific understanding of Mars's ancient habitability.