This is a drawing of the heliosphere.
Click on image for full size
"Helios" is the ancient Greek word for the "sun". The Heliosphere is the entire region of space influenced by the sun. That would include the regions of space which contain the IMF.
The magnetic field of the sun (the IMF) is enormous and is carried throughout space by the solar wind.
The solar wind and the IMF push back the Interstellar magnetic field and plasma of interstellar space. They create a bubble or cavity, within which the sun and planets reside. The boundary between space dominated by the sun and interstellar space is called the heliopause. No one knows just how far away the heliopause, or "edge" of the heliosphere is, but it could be as far away as 100 AU.
The Voyager 1 and Voyager 2 spacecraft have passed the orbit of Pluto. So, they are now exploring the environment of space. Scientists have received signals from both spacecraft that imply that the spacecraft are coming near the heliopause. For the spacecraft to pass beyond the heliosphere, they will first have to pass through a termination shock. They will then enter interstellar space where no spacecraft has ever gone before. It is thought that the Voyager probes will reach the termination shock in 2001-2002 and that they will be completely clear of the heliosphere by ~2008.
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