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.