Which NASA orbiter has operated around Mars longer than any other spacecraft?

NASA’s Mars Odyssey has operated around Mars longer than any other spacecraft. It entered Martian orbit on October 24, 2001, and remains an active mission, making it the longest continuously active spacecraft in orbit around another planet.

Odyssey was launched on April 7, 2001, from Cape Canaveral, Florida. Its primary scientific mission examined Mars’s surface composition and searched for water-related materials. A major early result came from its gamma-ray spectrometer and neutron detector, which helped reveal extensive hydrogen deposits consistent with water ice beneath the Martian surface, especially near the polar regions.

The orbiter is named after the 2001 science-fiction film 2001: A Space Odyssey, a naming choice that distinguishes it from Mars missions named after mythological figures or geographic features. Odyssey has also supported communications between Mars landers and Earth, relaying data from surface missions including NASA’s Spirit, Opportunity, Phoenix, and Curiosity.

Mars Odyssey is sometimes confused with Mars Global Surveyor, which arrived earlier in 1997, or Mars Reconnaissance Orbiter, which began orbiting Mars in 2006. However, neither remained operational around Mars as long as Odyssey.