Search for the global signature of the Martian dynamo

Abstract

We analyze Mars' global magnetic field observations to gain insight into the evolution of Mars and its paleodynamo. Statistical properties of the magnetic field above Noachian and Hesperian age crust are similar, suggesting that the dynamo persisted past the Noachian. We model crustal magnetization in order to match the large-scale features of the magnetic field. The model is based on a spherical shell of uniform thickness that was magnetized uniformly by an internal dipole. Crustal magnetization is removed from the northern lowlands, the Tharsis volcanic province, and the Hellas, Argyre, and Isidis impact basins. The magnetic field due to the remaining crustal magnetization is computed and compared with published models of the magnetic field data. The comparison is based on the spherical harmonic coefficients of the radial magnetic field component for the crustal magnetization models and the models of the observations. The correlation coefficients between the magnetization models and the models of the observations are calculated as a function of spherical harmonic degree. The correlations maximize for paleopole positions that are located near the equator in the southeast and northwest quadrants of Mars. The root-mean-square differences of the spherical harmonic coefficients are also calculated, and paleopole positions that minimize these differences generally agree with the paleopoles that maximize the correlations. The low-latitude to midlatitude paleopoles suggest that true polar wander occurred early in Mars history, and the polarity of the paleopole positions suggests that at least one reversal of the dynamo magnetic field occurred. Copyright © 2010 by the American Geophysical Union.