Earth's magnetosphere is the space surrounding the Earth beyond the layers of the atmosphere between 700 and 65 000 km of the surface.
This boundary, the magnetopause is the membrane that insulates us from interplanetary space dominated by the solar wind.
In this space is the Earth's magnetic field like a cocoon surrounding the Earth. In this area called Van Allen belts, energetic particles (protons and electrons) are organized around the Earth, depending on the magnetic field strength. This magnetic field acts as a shield deflecting the solar wind electric current which then flows outside the magnetosphere. The solar wind consists essentially of ions and electrons charged with considerable energy and expelled at a speed of ≈ 450 km/s, by thermonuclear reactions of our star.
The pressure of the solar wind compresses the magnetosphere Earth is facing the Sun, and stretches in the region of the magnetosphere at the rear, away from the Sun. The Earth's magnetosphere was described in 1958 during the measure by Geiger counters embedded in the first U.S. satellite, Explorer 1.
It is at this time that was discovered this area of space known as the Van Allen belt.
The Van Allen belt is composed of two parts with different characteristics. The first the closest to the earth is between 700 and 10,000 km altitude, it is constituted mainly of high-energy protons.
The second, the outer part is larger, it is between 13 000 and 65 000 km, it consists of high-energy electrons. All energetic particles traveling at high speed and are returned permanently to the poles of the magnetosphere. Thus, the solar wind never strikes the surface of the Earth directly. So we live in a magnetic bubble protected from deadly solar radiation.
Exposure, even of short duration to the flows densest of the Van Allen belt radiation is fatal to humans.
Few men have been on the other side of the magnetosphere against solar radiation death, only the Apollo astronauts who went to the moon crossed the Van Allen belt. Even with a protective shield, the exposure of astronauts was limited to less than an hour. As an invisible airbag, our magnetosphere is a key defensive barrier, a really shield magnetic.
But this magnetic shield is not homogeneous, it is constantly evolving and will change over time as a result of complex physical phenomena that occur in the Earth's core.
The geomagnetic field generated over 3 000 km below the surface flows from south magnetic pole, circle the globe, plunging underground to the core, at the north magnetic pole.
Much radiation passes along the magnetosphere without reaching the Earth's surface, but a small portion seeps at the austral poles and boreal where the geomagnetic field is weakest, this corresponds to an annular zone called "aurora zone", it situated now between 65 and 75 ° magnetic latitude.
When the solar particles seep into these rings, they collide with neutral gas atmosphere, colorful luminous phenomena are visible, more the solar wind is powerful and more light the sails are spectacular.
These bright features sails appear as a diffuse light curtain will move very quickly and stepped up to bring up huge light rays impressive.
The length of the aurora can measure thousands of kilometers, but its width usually does not exceed 100 meters. This beauty is misleading representation of a real battle between the deadly particles of the solar wind and protecting particles of the Earth's atmosphere.
Image: The Earth's magnetic field generated over 3000 km below the surface flows from south magnetic pole, circle the globe, plunging underground at the north magnetic pole. Much radiation passes along the magnetosphere without reaching the Earth's surface, but a small portion seeps at the austral poles and boreal where the geomagnetic field is weakest, this correspond to an annular zone called "aurora zone", it situated between 65 and 75 ° magnetic latitude.
True north and magnetic north does not match, the magnetic north in Canada, but it is not fixed, it moves about forty kilometers each year.
Without magnetosphere the planet would be directly affected by these energetic particles.
However, there is a place on Earth poorly protected where the magnetic field has weakened considerably. This area is located off the coast of Brazil, it is called the South Atlantic Anomaly or SAA, it covers 7.8 million km2 (≈ 2780 km by 2780 km) and it continues to grow.
Furthermore, the scientists noted that in this region the magnetic field is reversed and the solar radiation entering the upper atmosphere more deeply.
Above this point the cosmic radiation is closer and closer to the surface.
In this area, the altitude where planes fly, solar radiation are less filtered.
A 560 km altitude certain instruments of the Hubble Space Telescope are off during the crossing area. Scientists have some explanations about the South Atlantic anomaly.
A study of magnetite frozen in ancient pottery clay showed that 400 years ago the Earth's magnetic field was 10% stronger than today. Before each reversal of the magnetic field there is a decrease in intensity.
If the SAA is the manifestation of the reversal of the magnetic field, we will see a new inversion?
The geomagnetic field evolution over thousands of years has been analyzed in the carrots of volcanic lava because lava retains the direction and strength of the magnetic field at the time.
They thus show the reverse of the polarization of field. Geophysicists have listed 18,000 over the past 28 million years and each time the field strength drops significantly.
The last reversal occurred 750,000 years ago and many scientists believe we are currently witnessing a new and sudden reversal that will have huge consequences for life on Earth. We will see more auroras in places where there was none before.
Scientists are trying to understand how works the magnetic field. It seems that the geomagnetic field of the Earth is generated by interactions between the inner core and outer creating a giant dynamo.
It is this that generates a strong magnetic field and stable. Lines of the picture are against the magnetic flux which flow from south pole of the core and return to the sphere from the north pole.
In the earth's core, the currents of the solid inner core of the Earth heat the liquid outer core creating currents of particles around of the metal in fusion which rise and descend slowly.
Under the effect of the rotation of the earth this currents turn themselves creating the magnetic field which flows to the surface and extends into the space.
The Earth cooled slowly and when it will lost its internal heat, the liquid core will solidify and currents will stop flowing.
Mars has no global magnetic field but region sparsely magnetized.
Measurements made on samples of Martian meteorites have shown that Mars has lost its magnetic field, because during the first 50 million years Mars had a strong magnetic field.
Scientists do not know what has caused the disappearance of the Martian magnetic field.
Exposed to solar winds Mars became the barren red planet we know today.
Mars 2 times smaller than the Earth has cooled faster and dynamo stopped signing the death warrant of the planet.
Image: Lines of the picture represent the magnetic flux that flow from south pole of the core and return to the sphere from the magnetic north pole.