The shocked particles in the magnetosheath behind the solar wind bow shock cannot easily penetrate the Earth’s magnetic field. Because interplanetary field lines cannot penetrate our terrestrial field lines, and solar wind particles cannot escape the grip of interplanetary field lines. Because the plasma in the solar wind is highly conducting, its particles are ‘frozen’ within the magnetic field lines.

The boundary between the two regions is called the magnetopause and the cavity that the planet’s magnetic field creates in the solar wind is called the magnetosphere. The kinetic pressure of the solar wind distorts Earth’s magnetic field, causing its dayside to contract, and its nightside to expand, forming a magnetotail that extends beyond the Moon’s orbit.

The plasma of the magnetosphere consists mainly of electrons and protons. Some of them come from the solar wind and some from the Earth’s ionosphere. However, some He$^+$ and O$^+$ ions are also obtained from the ionosphere, and some He$^{++}$ ions come from the solar wind. This plasma is not uniform, the density and temperature are different from place to place.

Our radiation belt lies along Earth’s dipolar field lines at two to six Earth-radii. Here many high energy electrons oscillate between the northern and southern hemispheres along the magnetic field lines. Here the electron number density is 1 per cc, the temperature is approximately 50 million Kelvin, and the magnetic field strength is 100 to 1000 nanotesla.

Most of the plasma in the nightside magnetotail coalesces near the magnetic equator to form a single plasma sheet with a thickness of about 10 Earth radii. Near Earth this sheet descends all the way to the auroral ionosphere. Here, the average electron density is 0.5 per cc, the temperature is about 5 million Kelvin, and the magnetic field strength is about 10 nanotesla.

The outer part of the magnetotail is called the lobe. Here the electron density and temperature are very low. The electron number density is only 0.01 per cc, the temperature is 500,000 Kelvin, and the magnetic field strength is 30 nanotesla.