The beauty of having spacecraft that far outlive their expected lives is that they can corroborate and supplement data coming in from much newer missions. That's the case with our Voyager spacecraft as they continue their progress at system's edge. The Voyagers will be moving outside the heliopause in not so many years, and when they do, they will tell us much about the behavior of charged particles in the interstellar medium. This will bulk up incoming results from IBEX, the Interstellar Boundary Explorer spacecraft, as it studies the neutral particles that routinely penetrate the heliosphere. Our knowledge of true interstellar space is growing. It's at the heliopause that we see the boundary between the area defined by the solar wind flowing outward from the Sun and the interstellar medium that surrounds it. Racing outward at an average of 440 kilometers per second, the solar wind is pushing into a region of dust and ionized gas, inflating the bubble we know as the heliosphere. The...