Magnetopause

The magnetopause is the border between a magnetosphere and the surrounding plasma. For planetary science, the magnetopause is the border between the planet's magnetic field and the solar wind. The location of the magnetopause is figured out by the balance between the pressure of the dynamic planetary magnetic field and the energetic pressure of the solar wind. As the solar wind pressure increases and decreases, the magnetopause moves inward and outward in response. Waves (ripples and flapping movement) along the magnetopause move in the direction of the solar wind flow in response to small-scale different versions in the solar wind pressure and to Kelvin-Helmholtz instability.

Artistic version of the Earth's magnetopause. The magnetopause is where the pressure from the solar wind and the planet's magnetic field are equal. The position of the Sun would be far to the left in this image.

The solar wind is supersonic and passes through a bow shock where the direction of flow is changed so that most of the solar wind plasma is pushed-aside to either side of the magnetopause, much like water is pushed-aside before the bow of a ship. The zone of shocked solar wind plasma is the magnetosheath. At Earth and all the other planets with built-in magnetic fields, some solar wind plasma succeeds in entering and becoming trapped within the magnetic field around the Earth. At Earth, the solar wind plasma which enters the magnetic field around the Earth forms the plasma sheet. The amount of solar wind plasma and energy that enters the magnetic field around the Earth is controlled by the direction of pointing of the interplanetary magnetic field, which is deeply set within the solar wind.

The Sun and other stars with magnetic fields and stellar winds have a solar magnetopause or heliopause where the stellar environment is regional by the interstellar environment.