
Originally designed to operate for just one year around Mars, MAVEN’s mission was repeatedly extended, enabling the most extensive research into the workings of the Martian atmosphere ever attempted.
https://www.cbsnews.com/news/nasa-declares-end-mars-orbiter-maven-mission
Thanks to MAVEN, we know how the Mars atmosphere has been eroded by solar wind over billions of years. Designed to work for a single year, it operated for over eleven years.