At the end of the last millennium, numerous spacecraft were sent to Mars to begin exploration of that planet. Mars Global Surveyor is one of the successful missions that provided a detailed map of the topography and high resolution images of the surface, and also discovered unusually large remanent magnetism of the crust. Present-day anomalies indicate that Mars had at one time its own internal source of a planetary magnetic field from a magnetic dynamo resulting from motions of highly electrically conducting core material, similar to the dynamo that produces today's main magnetic field on Earth.