Current System Of Mars And Its Magnetic Field

Among eight planets in the solar system, the other planets have relatively strong intrinsic magnetic field except Venus and Mars. In view of their differences among all planets, especially their magnetic field topologies, the characteristics of interaction between planets and the solar wind are not the same and their magnetospheric structures and phenomena produced through interaction with solar wind are not the same. Mars among planets in the solar system is considered to be the most closest to earth in natural environment, so the human being are more and more concerned for Mars. Exploration and research of Martian magnetic field has become a hot topic in the field of space physics.In this thesis, based on facts that there is an ionosphere above the solid Mars but there is no intrinsic magnetic field inside the solid Mars, and also the characteristics of interaction between the solar wind and Martian ionosphere, a model of Martian induced magnetic field is proposed from the perspective of the current, and causes and the distribution of Martian induced magnetic field are studied. In addition, according to Martian aurora picture observed through spacecraft, a model of crustal magnetic field on Martian aurora zone is established, and topology of magnetic field lines is obtained, and the causes of magnetic anomalies are discussed. The main work and the results obtained are summarized as follows:Since there is no obvious intrinsic magnetic field at Mars, the characteristics of interaction between the solar wind and Mars are different from that of earth. The solar wind interacts directly with the Martian ionosphere and atmosphere, resulting on the appearance of the induced current on ionosphere. In the second chapter, a model of currents in the Martian magnetosphere is constructed based on the distribution of Martian magnetic field gained through satellite observations and the characteristics that the current always envelopes the magnetic field lines. In the model, the magnetopause current, the ionospheric current and the current sheet in magnetotail form the current system in Martian magnetosphere. According to the continuity of the current, these currents satisfy the relation that the total current in the Martian magnetopause is equal to the summation of the total current in the Martian ionosphere and the total current in the Martian magnetotail. This thesis discusses two-dimensional approximation model and three-dimensional distribution model of the current system in Martian magnetosphere respectively.In the third chapter, we construct two-dimensional approximation model and three-dimensional model of Martian induced magnetic field based on the current system model of Martian magnetosphere. In the model, Superposition of the magnetic field generated by these currents and solar wind magnetic field constitutes the distribution of magnetic field around Mars. According to Biot-Savart theorem, we get the distribution of magnetic field in Martian equatorial plane and the other plane parallel to equatorial plane using the program of tracing magnetic field lines. The results show the magnetic field distribution obtained by the model is consistent with observational results through satellite and those gained by others. Distribution of magnetic field around Mars is different from that of those planets having intrinsic magnetic field, and the magnetic field lines drape around Mars, forming an open structure in the magnetotail. Results also show that the topologies of magnetic field in different planes have both similarities and differences. In the plane parallel and closer to equatorial plane, the magnetic field lines drag more obviously, mainly because Martian ionosphere hinders interplanetary magnetic field at different extents in the different regions.Differing from auroras occurring on poles of planets with a strong intrinsic magnetic field, the Martian aurora occurs mainly in the region of crustal magnetic anomalies in southern hemisphere, and the distribution of the aurora differs from that of other planets. In the fourth chapter, from the equivalent currents point of view, we establish the model of the Martian crustal magnetic field on aurora zone, and gain the topology of crustal magnetic anomalies. Based on the fact that aurora occurs where the magnetic field lines converge, we can recover the Martian aurora morphology observed by Mars Global Surveyor and Mars Express through the topology of magnetic field according to the model. In addition, according to the obvious feature of the narrow width about Martian aurora arcs, the causes of the Martian crustal magnetic anomalies are discussed in this thesis.