THE HELIOSPHERE
The region of space governed by the Sun is called the heliosphere. This area is filled with plasma from the Sun in the form of the solar wind. Beyond the heliosphere, interstellar space exists, and it is filled with plasma from other stars. The heliosphere marks the division between the solar plasma and the interstellar plasma. It is the area where the pressure of the solar wind equals the pressure of the interstellar medium.
I understand that all this is hard to picture in your mind, but try to imagine the heliosphere as a kind of bubble that contains the solar system. It's a magnetic sphere that reaches beyond Pluto and is caused by the solar winds.
NASA's Cassini spacecraft suggests that the heliosphere may not possess the comet-like shape that scientists thought, but instead is more like a big, round bubble. This changes what they have thought for the past fifty years. The images indicate that the solar wind's interaction with the interstellar medium is instead more significantly controlled by particle pressure and the energy density of the magnetic field.
The Voyager spacecraft(s) have crossed the termination shock several time as it moves in and out from the Sun. This is due partly because of the pressure of the solar wind, which can increase or decrease as it flows from the Sun. Before reaching the heliosphere the solar wind is slowed from supersonic to subsonic speed, and this creates a shockwave called the termination shock.
So all this makes me wonder, when we have one, can our spacecraft travel safely beyond the heliosphere and withstand the termination shock? Can we protect the lives of the people inside? Of course, this means we are leaving our solar system. This is something to think about, one more thing to consider in space travel.
More information at http://www.universetoday.com/32519/heliosphere/
references: www.universetoday.com, www.cosmos4kids.com/files/solsyst2, http://helios.gsfc.nasa.gov/heliosph.html, www.sciencedaily.com/releases/2009/10/091016101807.htm
