The Mars Opportunity rover was expected to last for 91 days. It’s still going after 9 years!
The Mars Opportunity rover was launched from Earth on July 7, 2003. It landed on Mars on January 25, 2004. NASA scientists planned for Opportunity to be active or about 90 sol or Mars days.
However, it is still active in 2013 and has exceeded it's expected lifetime by 9 years and about 176 days. This is 38 times the lifetime it was designed for.
Throughout it's time on Mars, Opportunity has been reporting back scientific observations about the landscape. It discovered Martian meteorites and studied Victoria crater for two years. Opportunity's twin rover, Spirit, stopped moving in 2009 and lost communication with Earth in 2010.