Magnetosphere

Magnetosphere is the region around a planet in which charged atomic particles are influenced by the planet’s own magnetic field rather than by the magnetic field of the Sun as projected by the solar wind. Because Earth has its own magnetic field, the interaction of Earth’s magnetic field and the solar wind results in this very dynamic and complicated region surrounding Earth. As shown in the figure, studies by spacecraft and probes have now mapped much of the region of magnetic field structures and streams of trapped particles around Earth. The solar wind, a plasma of electrically charged particles (mostly protons and electrons) that flows at speeds of 1 million kilometers per hour or more from the Sun, shapes Earth’s magnetosphere into a teardrop, with a long magnetic tail (called the magnetotail) stretching out opposite the Sun.

Earth and other planets of the solar system exist in the Heliosphere, the region of space dominated by the magnetic influence of the Sun. Interplanetary space is not empty but filled with the solar wind. The geomagnetic field of Earth presents an obstacle to the solar wind, behaving much like a rock in a swiftly flowing stream of water. A shock wave, called the bow shock, forms on the sunward side of Earth and deflects the flow of the solar wind. The bow shock slows down, heats and then compresses the solar wind, which then flows around the geomagnetic field, creating Earth’s magnetosphere. The steady pressure of the solar wind compresses the otherwise spherical field lines of Earth’s magnetic field on the sunward side at about 15 Earth radii, or some 100,000 kilometers, a distance still inside the Moon’s orbit around Earth. On the night side of Earth away from the Sun, the solar wind pulls the geomagnetic field lines out to form a long magnetic tail, the magnetotail. The magnetotail is believed to extend for hundreds of Earth radii, although it is not known precisely how far it actually extends into space away from Earth.

The outermost boundary of Earth’s magnetosphere is called the magnetopause. Some solar wind particles do pass through the magnetopause and become trapped in the inner magnetosphere. Some of those trapped particles then travel down through the polar cusps at the North and South Poles and into the uppermost portions of Earth’s atmosphere. These trapped solar wind particles then have enough energy to trigger the Aurora, which are also called the Northern (aurora borealis) and Southern (aurora Australis) Lights because they occur in circles around the North and South Poles. These spectacular auroras are just one dramatic manifestation of the many connections among the Sun, the solar wind, and Earth’s magnetosphere and atmosphere.

Questions to Ponder

• How is the magnetosphere created?
• Does the magnetosphere affect weather?