Magnetosphere

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A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter, Saturn, Uranus, and Neptune. Jupiter's moon Ganymede has a small magnetosphere — but it is situated entirely within the magnetosphere of Jupiter, leading to complex interactions. The ionospheres of weakly magnetized planets such as Venus and Mars set up currents that partially deflect the solar wind flow, but do not have magnetospheres, per se.

The term magnetosphere has also been used to describe regions dominated by the magnetic fields of celestial objects, e.g. pulsar magnetospheres.

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History of magnetospheric physics

The Earth's magnetosphere was discovered in 1958 by Explorer 1 during the research performed for the International Geophysical Year. Before this, scientists knew that electric currents existed in space, because solar eruptions sometimes led to "magnetic storm" disturbances. No one knew, however, where those currents were and why, or that the solar wind existed. In August and September 1958, Project Argus was performed to test a theory about the formation of radiation belts that may have tactical use in war.

In 1959 Thomas Gold proposed the name "magnetosphere" when he wrote:

Earth's magnetosphere

The magnetosphere of Earth is a region in space whose shape is determined by the Earth's internal magnetic field, the solar wind plasma, and the interplanetary magnetic field (IMF). In the magnetosphere, a mix of free ions and electrons from both the solar wind and the Earth's ionosphere is confined by electromagnetic forces that are much stronger than gravity and collisions.

Despite its name, the magnetosphere is distinctly non-spherical. All known planetary magnetospheres in the solar system possess more of an oval tear-drop shape because of the solar wind.

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