“Offense is fine,” says one of the characters in Wizards at War to another, regarding the imminent invasion, “but you need defense too. How are we defining the defensive volume?”
The Planetary Senior for Earth indicates the surfaces of several concentric spheres, five hundred or eight hundred or a thousand AU out, and then points at the innermost volume, a hyperbolic solid rather than a spherical one. “But this is the ‘line in the sand’,” she says. “Nobody comes past the heliopause.”
It looks, though, as if Voyager 1 is slowly approaching that point (or zone) heading outward. Readings from the craft’s sensors suggest that it may be encountering the “terminal shock”, the point at which the Solar wind drops below the speed of sound. …Or maybe it isn’t: the experts are arguing about the results….
