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Figure 1. View of Mars from direction of the Sun on 21 September 1998 showing magnetic field vectors (light blue) along the orbit of the Mars Global Surveyor spacecraft. The distinctive fan-shaped field vector patterns shown at periapse are caused by two magnetic dipoles located just beneath the Martian crust in ancient heavily-cratered terrain in the vicinity of Cassini Crater. These dipoles show remnant magnetic crustal fields frozen into lava flows which occurred over 3.5 billion years ago during the time when Mars had an active planetary dynamo magnetic field. Clearly visible in this image of Mars are the Tharsis bulge with Olympus Mons and the three large Tharsis Montes volcanoes (light red area at lower left), the extensive Valles Marineris canyon (at lower right), created by enormous water floods billions of years ago on Mars, and the north polar ice cap (at upper left), made up of a mixture of carbon dioxide and water ice.
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