NASA’s Opportunity rover operated on Mars from 2004 until 2018, far beyond its planned 90-sol mission. It landed in Meridiani Planum on 25 January 2004, three weeks after its twin, Spirit, reached Mars.
Opportunity was designed to search for evidence that liquid water had once affected the Martian surface. It found geological features such as sedimentary rocks and hematite-rich spherules, supporting the conclusion that ancient Mars had wet environments.
The rover continued working for nearly 15 years, traveling more than 45 kilometers across the Martian surface, a record for extraterrestrial surface travel at the time. NASA declared the mission complete in February 2019 after a planet-wide dust storm prevented communication. Opportunity is often confused with Curiosity, which landed in 2012 and remains a larger, nuclear-powered rover.