Friday, 19 December 2014
John E P Connerney and Jared R Espley, Goddard Space Flight Center, Greenbelt, MD, United States
Observations acquired in orbit by the Mars Surveyor spacecraft require that the average Mars crustal rock be capable of acquiring magnetization intensities that greatly exceed those common on Earth. The Mars crust is at least 20 times more intensely magnetized, on average, than Earth's crust. The Mars crust formed by crustal spreading in the presence of a reversing dynamo, a continuous process that is capable of producing uniform volume magnetizations over global scale distances. No other proposed mechanism can match the efficiency of plate tectonics in this regard. We apply a novel downward continuation method to magnetic survey data acquired from orbit and show that at ever greater spatial resolution, the hallmarks of plate tectonics (magnetic lineations, transform faults) are evident in the magnetic imprint. Where catastrophic volcanic flows have buried the crust at great depth (volcanic edifices and the northern lowlands) the primordal magnetic imprint has been effectively erased. This indicates that the effective magnetic carrier in the crust is confined to a layer no more than a few km thick and that magnetization intensities of order ~100 A/m exist throughout the magnetized crust. The average Mars crustal rock must therefore be a rock that acquires impressive magnetization intensity cooling under conditions prevalent in the Mars crust some 4 billion years ago, during the dynamo age.