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 affected by the sun. The Heliosphere is like a bubble that has the planets and the Sun inside of it. Outside the bubble is interstellar space!
The Voyager 1 and Voyager 2 spacecraft have passed the orbit of Pluto. So, they are headed for the boundary of that Heliosphere bubble. That boundary between the Heliosphere and interstellar space is called the heliopause. They will then enter interstellar space where no spacecraft has ever gone before! The Voyager probes will probably reach the end of the heliosphere by ~2008. So, watch for the Voyager probes in the news!
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