The Mars Global Surveyor mission was decided after the loss of the Mars Observer probe in August 1993 but with very much less ambitious objectives because of budgetary restrictions imposed on NASA and a short development time. When it was operational, Mars Observer was to have provided important information for the sample return missions and carried 8 instruments.
Mars Global Surveyor (MGS) carried 6 of the 8 Mars Observer instruments and was launched in November 1996 by a Delta II rocket for a mission including mapping, geology, the study of the Martian atmosphere and interactions with the surface. MGS also had a mission to determine the magnetic properties of the planet and its mineral resources (in particular the distribution of minerals).
The American probe Mars Global Surveyor (MGS) successfully pursued its mission, begun in March 1999. For the scientists associated with the project, the MGS mission begun in 1999 was a real success. The probe achieved all its initial objectives in scrutinising Mars for one Martian year (687 terrestrial days).
MGS was used to lay the groundwork for the landing of the two rovers in the MER mission (Spirit et Opportunity in January 2005). And finally, the general state of the probe allowed NASA to go ahead with several mission extensions.