Our knowledge of Mars´ magnetic field has dramatically improved since the first observations carried out by the Mariner 4 spacecraft flyby in 1965. Those initial data, acquired at a distance from the Martian surface of 13,200 km, indicated the existence of a very weak global field, -clearly different from the Earth-like dipole magnetic field-, and a shock-like disturbance in the near-Mars solar wind. Since then, research has been mainly directed towards these two initial findings and to obtain a more complete picture of the magnetic field created by Mars and the way this field interacts with the solar wind.
Thanks to many spacecraft missions (especially Mars Global Surveyor and Mars Express) we presently know that Mars, unlike Earth, has no global magnetic field able to influence its near environment and interact with the solar wind. The average intensity of the magnetic field at the Martian surface is smaller than 5nT, which corresponds to a dipole moment of less than 1018 Am2, far from the 1022 Am2 of the Earth´s magnetic dipole. However, the Mars Global Surveyor revealed the existence of intensely magnetized regions in the Martian surface which, due to the absence of a global magnetic field, can be considered as vestiges of an ancient, planetary scale field. The intensity of this remanent magnetization reaches about 10 times that observed for the Earth and requires the presence of very strongly magnetic rocks and magnetization in a 30 km-thick crust. The existence of magnetic disruption near well-dated large impact craters indicates that the magnetization process (and the dynamo which originated the global field) ceased more than 4.5 Ga ago. Why and how the dynamo stopped remains a controversial subject. In the same way, the location of most of these anomalies in the southern hemisphere and their distribution (in some cases) in stripes with alternatively positive and negative polarity (as in the spreading zones of the Earth´s oceanic crust) raise new questions about the thermal history and tectonic activity of Mars.
Radio occultation soundings and in situ measurements by different Mariner, Mars and Viking vessels, and more recently radar soundings obtained by the Mars Express, are illustrating the main features of the Martian ionosphere. A maximum electron density of 2x105 cm-3 on the dayside of Mars has been recently proposed. This value is lower than those which characterize the Earth´s ionosphere F layer and shows that the Sun is less effective at ionizing the Martian atmosphere. Several different models of the ionosphere with two or three layers located between 60 and 500 km, are currently in discussion. It seems that the Chapman model deduced for the ionosphere of the Earth can also be applied to fit electron density profiles obtained for Mars. With respect to the interaction of the Mars magnetic field with the ionosphere, radar soundings have revealed the existence of upward bulges in the ionosphere above regions where the crustal magnetic field is particularly strong and nearly vertical. The first observed Martian aurora (2005) took place above a crustal magnetic anomaly close to the equator, as opposed to near the poles as occurs on Earth. This confirms the important role that the areas with a strong local magnetic field seem to play in this phenomenon.
The comparative study of the Earth and Mars magnetic fields can cast light on issues such as the evolution of the core of our planet, the level of tectonic activity, the future of its atmosphere, and even the origin of life on Earth. This is why the results of this field of research are so appealing.
The study of the Mars magnetic field in the frame of the MEIGA-MetNet Project will pay special attention to the following topics:
- Comparison of the Earth and Mars magnetic fields main features and study of its tectonic implications
- Modeling of charged and magnetized particles/dust movement inside the Mars magnetic field
- Study of the Mars Ionosphere and is interaction with crustal magnetic anomalies
- Analysis of the magnetic data taken by the MEIGA-MetNet magnetometer. It is worth remarking that this magnetometer will be the first one ever placed on the Mars surface