Magnetosphere

see also: Etymology of Magnetosphere

The magnetosphere is the area surrounding a Celestial object in which the physical phenomena are dominated or organized by its Magnetic field.

Any planet equipped with a magnetic field (the Ground, Jupiter, Saturn, Uranus and Neptune) has its own magnetosphere. Mercury and Ganymède, the moon of Jupiter, also has one of them, but these magnetospheres are too weak to capture the ionized solar wind. On Mars, one observed local magnetic anomalies in the planetary bark, supposed remainders of an ancestral magnetic field nowadays disappeared. The term “magnetosphere” is also used to describe an area dominated by magnetic fields of several celestial objects.

The terrestrial magnetosphere is located beyond the Ionosphère, i.e. above 800 to 1.000 km of altitude. If there were no Solar wind, the magnetic Specter of the Earth would be similar to that of a Aimant isolated right. Actually, the magnetosphere acts like a screen and protects terrestrial surface from excesses of the solar wind, harmful for the life. She is opposed to the solar wind as an abutment of bridge deviates the current of a river. N the other hand the solar wind deforms the magnetic spectrum of the Earth by giving him the comet shape, as the figure shows it schematically below.

History of the Magnetosphere

The magnetosphere was discovered in 1958 by the probe Explorer 1 during research of IGY (International Geophysical Year). Front, the scientists knew that electric currents ran out in space, because the solar eruptions caused sometimes magnetic disturbances. In August and September 1958, the Projet Argus tested a theory on the formation of bells of radiation being able to be used with the war.

In 1959 Thomas Gold proposed the term of magnetosphere , when he wrote:

"The area with the top of the ionosphere in which the magnetic flux of the Earth has a contôle dominating over gases and particles charged fast is known to extend at a distance from 10 times the terrestrial ray; its suitable name pourait being magnétosphère." Newspaper Geophysical Results' LXIV. 1219/1

Structure of the magnetosphere

The Sun is apart from the figure, on the left. The solar wind is represented by three parallel arrows but, actually, it runs out on both sides of the magnetosphere, the limit between this one and the interplanetary Milieu being the magnetopause (Mp reference mark) which is to approximately 60.000 km of the Earth (foot-note: the figure is not on the scale). In front of the magnetopause is the surface of shock (reference mark S), place where solar plasma is strongly slowed down before running out in the magnétogaine (reference mark Mg), zone of turbulence ranging between the surface of shock and the magnetopause. In the polar regions, side of the Sun ( side day), are the polar horns (reference mark CP). The polar horns act as of the funnels in which the electrified particles of the solar wind can penetrate and cause the appearance of polar lights. The dawns, boreal in the northern hemisphere, southern in the the Antarctic, are formed in the auroral zones north and south (Za reference mark).

side harms , the lines of field are not closed again and constitute the tail with the neutral layer and the layer of plasma. The tail is stretched with more than 300.000 km in the direction opposed to the Sun.

To less few thousands of kilometers of terrestrial surface an annular zone (Zp reference mark) placed in the plan of the magnetic equator is in which electrified particles, protons and electrons coming from the solar wind, can find trapped by the magnetic field. It is there that are formed the Van Allen radiation belts or belts of radiations .

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