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Concept

Heliopause

A glowing ring structure resembling Saturn's rings is depicted against a dark background, symbolizing the concept of the heliopause, where the solar wind meets the interstellar medium.

The boundary at which the solar wind, blown outward from the Sun, is finally stopped by the pressure of the surrounding interstellar medium. It marks the outer edge of the heliosphere and, by one common definition, the beginning of true interstellar space. Voyager 1 crossed it in August 2012 at roughly 121 astronomical units from the Sun.

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