Mars Global Surveyor

The Mars Global Surveyor (MGS) spacecraft was launched in 1996 to orbit the red planet and collect images of the surface using various instruments including the Mars Orbiter Camera (MOC), the Thermal Emission Spectrometer (TES), and the Mars Orbiter Laser Altimeter (MOLA). The spacecraft’s mission was to monitor and observe long-term trends in Mars’ atmosphere, collect data on geologically significant areas on the surface, and provide support for future Mars missions. Mars Global Surveyor accomplished all these objectives, remaining in contact with scientists for four times longer than initially expected. 

"After a 20-year absence at the planet, Mars Global Surveyor ushered in a new era of Mars exploration with its five science investigations. Mars Global Surveyor arrived at Mars on September 11, 1997 (September 12, UTC), and has contributed a multitude of findings, including signs of past, persistent water such as an ancient delta and currently active water features in the gullies of canyon walls." 
"Among key science findings so far, Global Surveyor has taken pictures of gullies and debris flow features that suggest there may be current sources of liquid water, similar to an aquifer, at or near the surface of the planet...Data from the spacecraft's laser altimeter have given scientists their first 3-D views of Mars' north polar ice cap." Read more at the MGS main homepage.