Darkness on the Edge of Town.

Twenty-eight years into its tour of the universe, Voyager I reaches the edge of the solar system. "[P]roject scientists, working from models of a phenomenon never before directly observed, finally agreed that data from Voyager 1's tiny 80-kilobyte computer memory showed that the spacecraft had passed through termination shock to the 'heliosheath,' a frontier of unknown thickness that defines the border with interstellar space."