An artist’s impression of the 2001 Mars Odyssey spacecraft
Credit: NASA/JPL

On 15 December 2010, NASA’s 2001 Mars Odyssey spacecraft will have operated for 3,340 days, in orbit  around Mars, breaking the longevity records of all previous Mars missions. 2001 Mars Odyssey was launched into space on 7 April 2001, and entered orbit around the Red Planet more than six months later, on 24 October 2001. Its primary target was to search for evidence of past or present water and volcanic activity on Mars.

Mars Odyssey carries three main science instruments on board. It made its most famous discovery, evidence for abundant water ice immediately below the dry surface of Mars, during its first few months, and it investigated the radiation-safety of Mars for proposed future manned missions to the planet, before the end of its prime mission, in 2004. Many unique accomplishments have been made, during the extra years of extended Odyssey mission, since then.

The long duration of the Mars-orbiting spacecraft has allowed Odyssey scientists to monitor seasonal changes on Mars, such as the cycle of carbon-dioxide freezing out of the atmosphere in polar regions, in each Martian hemisphere's winter. 
Mars Odyssey has aided other Martian missions, including the twin Mars Exploration Rovers, Spirit and Opportunity. Images and data acquired by the rovers have reached Earth via Odyssey, which receives signals from both rovers, daily. 

NASA has published an interesting picture gallery, featuring remarkable images from Mars Odyssey, at the link below.
http://www.nasa.gov/mission_pages/odyssey/images/all-stars.html   

"Hundreds of people who built the Odyssey spacecraft here, in addition to the much smaller crew operating it today, have great pride in seeing the spacecraft achieve this milestone," said Bob Berry, Odyssey program manager.

Odyssey orbits Mars in a circular orbit, at an altitude of about 400 km. The name "2001 Mars Odyssey" was selected as a tribute to the vision and spirit of space exploration as embodied in the works of famous science fiction writer Arthur C. Clarke, including one of his most celebrated works, 2001: A Space Odyssey.

References

NASA Press Release

http://www.nasa.gov/mission_pages/odyssey/odyssey20101209.html

Wikipedia

Further Reading

NASA’s Mars Odyssey Homepage

http://www.nasa.gov/mission_pages/odyssey/index.html

Mars Odyssey Website

http://mars.jpl.nasa.gov/odyssey/index.cfm

Aymen Mohamed Ibrahem

Senior Astronomy Specialist