Mars Global Surveyor orbited Mars for 9 years, 1997–2006

NASA’s Mars Global Surveyor launched on November 7, 1996, began orbiting Mars in September 1997 and worked for nine years and 52 days, longer than any spacecraft sent to Mars before it, until its last contact on November 2, 2006.

Even its arrival has two dates: JPL’s releases give September 11, 1997, NASA’s History Office September 12. It then spent 18 months aerobraking, dipping into the thin upper atmosphere to shrink a long ellipse into a near-circular mapping orbit, a technique it pioneered at Mars. Mapping began in April 1999. The plan was one Mars year, nearly two Earth years; it ended up studying Mars four times as long as originally planned.

“It is an extraordinary machine that has done things the designers never envisioned despite a broken wing, a failed gyro and a worn-out reaction wheel.” — Tom Thorpe, JPL project manager, 2006

Surveyor returned more than 240,000 images. Its spectrometer found fine-grained hematite, a mineral that often forms in water, which led NASA to send the Opportunity rover there. Its laser altimeter produced an unprecedented global topographic map, and its magnetometer found remnant magnetic fields showing Mars once had a global field like Earth’s.

Its most famous finding has aged less well. NASA hailed Surveyor’s before-and-after images of bright new deposits in two gullies as the strongest evidence to date that liquid water still flows occasionally on Mars. From 2006, Mars Reconnaissance Orbiter’s HiRISE camera monitored gullies at 356 sites; new activity at 38 of them coincided with seasonal carbon-dioxide frost and temperatures too cold for liquid water. NASA concluded in 2014 that the gullies are formed primarily by freezing carbon dioxide.

The orbiter’s end was self-inflicted. A 2007 review board traced it to a computer error made five months earlier. After a routine solar-panel adjustment, the craft turned so that one battery faced direct sunlight; it overheated, and both batteries were likely drained within about 11 hours.