heliosphere

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heliosphere

(hee -lee-ŏ-sfeer) The vast region around the Sun that is permeated by the solar wind and the weak interplanetary magnetic field, and in which the solar-wind plasma plays a dominant role. It is bounded by the heliopause, which is estimated to be 100 AU or more from the Sun's center but has not yet been encountered by any spacecraft. The heliosphere may be very elongated owing to the presence of an interstellar wind of neutral hydrogen flowing from the direction of the galactic center.

heliosphere

[′hē·lē·ə‚sfir]
(astronomy)
The region surrounding the sun where the solar wind dominates the interstellar medium. Also known as solar cavity.
(geophysics)
The region in the ionosphere where helium ions are predominant (sometimes there may be no region in which helium ions dominate).