The heliosphere is the region of space, surrounding the Sun, which is inflated by the solar wind and within which the Sun exerts a magnetic influence. Despite its name, the heliosphere is almost certainly greatly elongated due to the movement of the Sun with respect to the interstellar medium. It is bounded by the heliopause. Between the heliopause and the bow shock is presumed to be a layer of interstellar gas known as the heliosheath.

Data returned by Pioneer 10, Voyager 1, and Voyager 2 (contact with Pioneer 11 has been lost), as these probes head for interstellar space, will help further characterize the heliosphere.