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A magnetopause flows along the boundary between a magnetic field, (see: magnetosphere) and surrounding plasma. It behaves roughly like a droplet of liquid exposed to supersonic flow. The magnetopause will ripple, flap, and sometimes droplets will break off.

In planetological terms, the magnetopause is the location where the outward magnetic pressure of the Earth's magnetic field is counterbalanced by the solar wind, a plasma. Most of the solar particles are deflected to either side of the magnetopause, much like water is deflected before the bow of a ship. However, some particles become trapped within the Earth's magnetic field and form radiation belts.

See also heliopause, magnetosphere, shock wave and solar system, Van Allen radiation belt.

For applications to spacecraft propulsion see magnetic sail.