Magnetosphere

A magnetosphere is the region of space in which the magnetic field of an object (e.g., a star or planet) dominates the radiation pressure of the stellar wind to which it is exposed.

Not all planets have a magnetosphere. In some rocky worlds it is caused by the molten iron-nickel core and aligned with the north and south poles, and helps to shield against cosmic radiation. The magnetosphere extends some distance into space (depending on the strength of the local planetary magnetism) and is influenced by the solar wind. It is teardrop shaped - being longer in the side facing away from the system primary (the magnetotail.)