Analysis of Mars Global Surveyor magnetic data: Crustal and time-dependent external magnetic fields.

摘要

In this thesis, Mars Global Surveyor mapping-phase magnetic data are used to derive a combined spherical harmonic model of both Martian crustal and time-dependent external magnetic fields.; A 60-degree spherical harmonic model of the crustal magnetic anomalies is first isolated, by averaging of in-shadow data over 0.5° x 0.5° latitude and longitude bins, and covariance analysis between multiple independent models. This model is then subtracted, separately, from day-side and night-side measurements. External residual data are expended in terms of now time-dependent 30-degree spherical harmonics, using 1 year and ½ year periods, and with separate internal and external radial dependencies. Independent Fourier series expansions allow to validate the temporal variations of the preceding model.; As a result, I obtain, along with the crustal anomaly maps, the spatial distribution of the external fields, their steady-state features, and the amplitude maps of their yearly and half a year variations, separately for day and night sides of Mars. Although the maxima of the temporal amplitudes show good correlations with the strong crustal anomalies, there are significant differences between them.; Keywords. covariance analysis, crustal anomalies, magnetic anomalies, magnetic field, magnetosphere, Mars, Mars Global Surveyor, spherical harmonics, temporal amplitudes