Termination shock

I can't help it, I think this is fascinating and weird. I read in the Post Standard this week that Voyager 2 is approaching the termination shock, and I just had to look up such a dramatic phrase. Here is a pretty technical explanation from Wikipedia:

The point where the interstellar medium (the gas and dust that pervade interstellar space; the matter that exists between the stars within a galaxy) becomes subsonic is the bow shock; the point where the interstellar medium and solar wind pressures balance is at the heliopause; the point where the solar wind becomes subsonic is the termination shock.

Here's what I read about Voyager:
http://www.nature.com/news/2007/071210/full/news.2007.365.html

Like a soft orange that fell just a bit too hard from its tree, the giant bubble that protects [our]solar system from interstellar space is squashed on one side, new data show.

On 30 August, NASA’s Voyager 2 spacecraft — which has been sailing through space since 1977 — crossed the ‘termination shock’, the boundary between the bubble in space dominated by the solar wind coming from the Sun and the transition region beyond that lies between Earth and interstellar space.

Voyager 2’s twin, Voyager 1, crossed this same boundary in December 2004. But Voyager 2 did it while almost 1 billion miles closer to the Sun, suggesting that something — such as an interstellar magnetic field — is compressing the bubble of the solar wind on that side.

The twin Voyagers headed out of the solar system in different directions, with Voyager 1 taking a northern path and Voyager 2 a southern one.
[snip]
Voyager 2 actually captured the crossing at least five times, as the termination shock washed back and forth over the spacecraft like a wave on a beach.

Within a decade, both spaceships will move out of the transition region and into true interstellar space — becoming the first manmade objects to fully exit the solar system. Radioactive generators aboard each spacecraft, powering their electrical systems, may allow them to transmit through the transition and beyond.

Voyager 1 is currently nearly 10 billion miles from the Sun, travelling nearly a million miles a day. Voyager 2 is nearly 8 billion miles away, and moving just slightly slower.