Crustal magnetic field of Mars

Abstract

The equivalent source dipole technique is used to model the three components of the Martian lithospheric magnetic field. We use magnetic field measurements made on board the Mars Global Surveyor spacecraft. Different input dipole meshes are presented and evaluated. Because there is no global, Earth‐like, inducing magnetic field, the magnetization directions are solved for together with the magnetization intensity. A first class of models is computed using either low‐altitude or high‐altitude measurements, giving some statistical information about the depth of the dipoles. Then, a second class of models is derived on the basis of measurements made between 80 and 430 km altitude. The 4840 dipoles are placed 20 km below the surface, with a mean spacing of 2.92° (173 km). Residual rms values between observations and predictions are as low as 15 nT for the total field, with associated correlation coefficient equal to 0.97. The resulting model is used to predict the magnetic field at 200‐km constant altitude. We present the maps of the magnetic field and of the magnetization. Downward continuation of a spherical harmonic model derived from our equivalent source solution suggests that intermediate‐scale lithospheric fields at the surface probably exceed 5000 nT. Given an assumed 40‐km‐thick magnetized layer, with a mean volume per dipole equal to 3.6.106 km3, the magnetization components range between ±12 A/m. We also present apparent correlations between some impact craters (≥300‐km diameter) and magnetization contrasts. Finally, we discuss the implications of the directional information and possible magnetic carriers.