Magnetosphere

A magnetosphere is the volume of space around an astronomical object that is controlled by that object’s magnetic field. The Earth’s magnetosphere is the cavity formed by the Earth’s magnetic field in the flow of plasma from the Sun known as the solar wind. The interaction with the solar wind deforms the Earth’s basically dipolar magnetic field, compressing the field lines on the day side and stretching them out to form a long comet-like tail on the night side. On the day side, the magnetosphere extends out to a distance of approximately 10 Earth radii, while the magnetotail extends several hundred Earth radii in the antisunward direction. The magnetosphere contains various large-scale regions, which vary in terms of the composition, energies, and densities of the plasmas that occupy them. The sources of the plasmas that populate these regions are the solar wind and the Earth’s ionosphere; the relative contributions of these two sources to the magnetospheric plasma vary according to the level of geomagnetic activity.