Defines the edge of the Solar System. It's the region where the pressure of the local interstellar medium equals that of the solar wind and therefore the solar wind cannot expand further into space.
The Heliopause is located about 125 AU or 19 billion kilometres (12 billion miles) from the Sun. The only man-made object to have passed through the Heliopause and therefore into interstellar space is Voyager 1.
