This is a map of the vertical (radial) component of magnetic fields originating from the Martian crust, obtained by the magnetometer aboard Mars Global Surveyor, overlaying a photo of the Martian surface. The strength of the magnetic field is very low in the northern lowlands, deep impact basins, and Tharsis volcanic province, but high in part of the ancient southern crust undisturbed by giant impacts or volcanism. That area also appears to have a banded structure to the magnetic field, with alternating strips of inward- and outward-flowing magnetic field lines.

NASA / University of California, Berkeley