Heliopause

The region in space where the Sun's atmosphere merges with interstellar space. The position of the heliopause depends both on the strength of the solar wind and on the properties of the local interstellar medium. Note also that data from Ulysses during solar minimum have shown that the solar wind from the Sun's poles has a higher speed than the speed in the ecliptic, so then the heliopause should be further from the Sun in the polar direction.