"Mars Crustal Magnetism: Part II"
The surprising discoveries by Mars Global Surveyor of Mars' crustal magnetism were greatly expanded during the second aerobraking phase of this mission in 1999. MGS used aerobraking to circularize it's highly elliptical polar orbit with minimal propellant consumption, allowing the sampling of vector magnetic fields just above the surface of Mars, at altitudes greater than 100 Km. The initial observations of scattered and strongly magnetized regions in the crust were extended to cover most of the planet revealing even stronger magnetization and an amazing correlation between the age of the terrain and the location of the magnetic sources. Mars crustal magnetization greatly exceeds that of our own planet and is largely confined to the most ancient, heavily cratered Mars highlands. The global distribution of magnetization is punctuated by major impact basins that formed before and after the cessation of the early Mars dynamo. Groups of quasi-parallel linear features of alternating magnetic polarity are found. They are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on Earth but with a much larger spatial scale (2,000 Km long, 200 km wide, limited by our spatial resolution, compared with about 20 km on Earth). These "magnetic stripes" may have formed on Mars just as they form on Earth, by crustal spreading and cooling in the presence of a reversing dynamo field, a key component of plate tectonics. Alternatively, strong tectonic activity may have fractured an ancient magnetized crust to create the observed signatures. Mars offers the first example of a planet where the main dynamo generated field has ceased to exist leaving behind a "pure" imprint of crustal magnetization of great interest to planetary scientists and geophysicists.