This month the Planetary Society is “celebrating 10 years on Mars with the Mars Exploration Rovers” with a virtual on line party: Happy Birthday Opportunity! – The Planetary Society
The Spirit rover landed on January 4, 2004 and Opportunity landed on January 25, 2004. The baseline plan saw each rovers working for 90 days. However, Spirit remained operational until March 4, 2010 and Opportunity is still actively exploring Mars.
You can send a message congratulating the Mars Exploration Rovers (MER) team: Send a Message to the MER Team – The Planetary Society.