= Heliosphere
The <heliosphere> is the region of space dominated by the solar-wind <plasma> and its carried <magnetic field> as they interact with the interstellar medium. The solar wind slows at the <termination shock> and encounters the interstellar <plasma> at the <heliopause>.
This is a plasma-interaction boundary, not the outer reach of the Sun's gravity or <light>. Voyager observations combine particle, magnetic-field and plasma-wave measurements to diagnose the transition. An increased local <electron> density outside the heliopause supplied an important independent diagnostic, illustrating why a boundary cannot always be identified from one field direction alone.<NASA Spacecraft Embarks on Historic Journey into Interstellar Space by NASA>[Solar/interstellar plasma distinction and Voyager plasma-wave diagnostic]{ref}
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