ESA has published the most detailed map ever created of the Earth’s magnetic field using data collected over three years of the mission of its three Swarm satellites. For this work, data collected by the German CHAMP (Challenging minisatellite Payload) mission in the last decade were also used together with new modeling techniques. The result was the extraction of the tiny magnetic signals from the Earth’s crust.
The three Swarm satellites were launched on November 22, 2013 with the specific purpose of improving our knowledge of the Earth’s magnetic field, the cocoon that protects the planet from the solar wind and other cosmic radiation. Most of this magnetic field is generated at a depth of more than 3,000 kilometers (almost 1,900 miles) in an activity comparable to that of a dynamo of the liquid iron in the core’s outer layer.
However, approximately the 6% of the Earth’s magnetic field is generated in part by electric currents in the space around the Earth and in part by magnetized rocks in the upper lithosphere, consisting of crust and upper mantle. This part is the most difficult to observe from space because of its weakness and a goal of the Swarm mission was precisely to do that. That was done as well and the map created also includes that part of the magnetic field.
The measurements taken from space are very important because they allowed to create a detailed global view of the magnetic structure of the Earth’s rigid outer part. The use of satellites since previous missions is due to our inability to directly study the crust and the core because the drilling can reach a very limited depth compared to those which would be useful to make direct examinations.
The new map shows the variations in the magnetic field caused by geological structures in the Earth’s crust. They include some anomalies, for example there is one around the city of Bangui in the Central African Republic, where the magnetic field is much stronger. One hypothesis is that this is the result of a meteorite impact occurred about 540 million years ago but it’s to be verified.
Other information contained in the new map cover the reversals of the magnetic poles and the stripes formed by minerals solidified at the bottom of the seas. These are recordings of the Earth’s magnetic field history that can be analyzed to try to predict the next reversal but also to study the movements of tectonic plates.
The mission of the Swarm satellites continues and the hope is that they can get even more accurate details during the minimum period of solar activity. The results are already excellent, also in unexpected ways such as the contribution to the discovery of the link between the black out of GPS navigation systems in low orbit and the “thunderstorms” in the ionosphere.