Large Image of the Helix Nebula (100K)
The goal of the Voyager Interstellar Mission is to move out of the "bubble" blown around the sun by the solar wind and into the the unperturbed interstellar medium.
What would the heliosphere look like if we could see it from the outside?
Something like this image of the Helix Planetary Nebula, photo courtesy of David Malin (for a review of the properties of this nebula, see the article by Noam Soker in Scientific American, May 1992, page 78).
Large Image of the Helix Nebula (100K)
Although the physics of planetary nebulae is different in many details from that of the heliosphere, there is one important similarity--in both cases the central objects blow bubbles in the local interstellar medium by ejection of mass. The central region in this image of the Helix Nebula consists of a high velocity wind (1000 km/sec) like the solar wind, except that it is much much more massive (a million times more mass flux as compared to the solar wind). It is thus able to blow a much bigger bubble in the interstellar medium (by a factor of the square root of the relative ram pressures, or about 1000 times bigger--see eq. 1 of the review by Axford and Suess).
Thus, whereas the heliosphere is only a light day across, the bubble blown in the image above is five light years across!
The Helix Nebula wind also goes through a shock transition and there is an additional shock in the interstellar medium as the material from the central object moves through the interstellar medium. An overexposed version of the above image shows this latter transision more clearly (upper left part of the image below).
Large Overexposed Image of the Helix Nebula
(100K)