The boundary where the solar wind meets and is stopped by the interstellar medium, marking the edge of the heliosphere. This region represents the furthest extent of the Sun's direct influence in space.
From Greek 'helios' (sun) and 'pause' from Greek 'pausis' (stopping). The term emerged in the 1960s when scientists theorized about where the solar wind would eventually be halted by the pressure of interstellar gas and magnetic fields.
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