NASA's Mars Odyssey orbiter has become the longest-serving spacecraft at the Red Planet. Launched in 2001, the craft has been in orbit around Mars for 3,340 days. The previous record was set between 1997 and 2006 by NASA's Mars Global Surveyor.
NASA explains Odyssey's mission:
Odyssey's longevity enables continued science, including the monitoring of seasonal changes on Mars from year to year and the most detailed maps ever made of most of the planet. In 2002, the spacecraft detected hydrogen just below the surface throughout Mars' high-latitude regions. The deduction that the hydrogen is in frozen water prompted NASA's Phoenix Mars Lander mission, which confirmed the theory in 2008. Odyssey also carried the first experiment sent to Mars specifically to prepare for human missions, and found radiation levels around the planet from solar flares and cosmic rays are two to three times higher than around Earth.
The spacecraft has also served as a communications relay between Earth and other scientific probes sent to Mars.
If the highlight video (above) leaves you wanting more, NASA runs a website that fully documents Odyssey's ongoing Martian exploration.