On June 10, 2003, NASA launched the Spirit rover on its mission to Mars. It preceded the twin rover Opportunity, which launched on July 7. Spirit landed on Mars on January 4, 2004.

Spirit was intended to operate for 90 days, but it continued functioning for six years, thanks in part to wind blowing dust off its solar panels. The rover had a flaky front wheel, but its other five were fine—leading mission controllers to drive the rover backwards, dragging the broken wheel for a total of 4.8 miles on the Martian surface.

Spirit became permanently stuck in the soil in 2009 and stopped communicating in 2010. Over its service lifetime, Spirit sent back 128,224 images. (Opportunity is now over 220,000.)

The twin rovers are active on Twitter, with Opportunity nicknamed "Oppy." The twins have now provided nearly a decade and a half of on-the-ground science. To further understand the rovers' success, check out this NASA documentary made five years into their mission:

If you're interested in the current status of Opportunity science, NASA has you covered.