On December 11, 2005, Opportunity, one of the twin rovers exploring Mars, celebrated its first Martian birthday. Opportunity had been on the red planet 687 Earth days, which is one Martian year. (A year is the time it takes a planet to make a complete loop around the sun). Join us for a look back over the those 687 days of discovery: what we learned, what we saw, and what questions remained unanswered.