Mars Global Surveyor Magnetic Field Experiment

Abstract: Mars currently has no global magnetic field of internal origin, but must have had one in the past, when the crust acquired intense magnetization¹, presumably by cooling in the presence of an Earth-like magnetic field (thermoremanent magnetization or TRM). The Mars crust is about an order of magnitude more intensely magnetized than that of the Earth^2,3. The apparent lack of magnetization associated with major impact basins and volcanic provinces suggest that the crust acquired magnetic remanence early in its history and that the dynamo was inactive at the time of the last major impacts, about 4 billion years ago⁴. A new map of the magnetic field of Mars, compiled using measurements acquired at ~ 400 km mapping altitude by the Mars Global Surveyor spacecraft, is presented here⁵. The spatial resolution and sensitivity of this global map is unprecedented, inviting geologic interpretation heretofor reserved for aeromagnetic and ship surveys on Earth. These data provide new insight into the origin and evolution of the Mars crust. Variations in the crustal magnetic field appear in association with major faults, some previously identified in imagery and topography (Cerberus Rupes, Valles Marineris). Two parallel great faults are identified in Terra Meridiani by offset magnetic field contours. They appear similar to transform faults that occur in oceanic crust on Earth, and describe the relative motion of two ancient Mars plates on the surface of a sphere. The magnetic imprint in Meridiani is consistent with that observed above a mid-ocean ridge on Earth. It is a relic of an era of plate tectonics on Mars, an era of crustal spreading, rifting, plate motions, and widespread volcanism following the demise of the dynamo. We present this new data in the context of the early development of plate tectonics on Earth, as advanced by the Vine-Matthews⁶ hypothesis and the work of W. Jason Morgan⁷ and others.