Opportunity is a Mars rover that has driven over 40 km (25 miles), the furthest roving distance of any space probe. Opportunity launched a month after its twin rover, Spirit, landing on the opposite side of Mars from it, inside Eagle Crater. Evidence from Opportunity suggests that Eagle Crater was once the shoreline of a salty sea on Mars. Together, Spirit and Opportunity formed NASA’s Mars Exploration Rovers (MER) Program, acting as robotic geologists in search of answers about the history of water on Mars. While Spirit lost communication with Earth in 2010, Opportunity has continued operations for several years past its original 90 day mission. From Eagle Crater, Opportunity roamed on to explore Endurance Crater, Erebus Crater and Victoria Crater. Recently, one of Opportunity’s seven memory banks has been failing as a result of its age, but the six remaining continue to survive.