When Voyager I and II left Earth, Jimmy Carter was president, platform shoes were all the rage and moviegoers were still discovering a summer blockbuster called Star Wars.
Some 35 years later, the spacecraft have traveled farther than anything ever built by humans. Now there is evidence one of the plucky probes may soon cross the undulating boundary between the absolute edge of our solar system and the terra incognita of interstellar space.
"It's not that clear because there's no signpost telling you that you're now leaving the solar system, but the evidence is mounting that we're getting really close," says Arik Posner, a Voyager program scientist at NASA's headquarters in Washington, D.C.
That boundary is a mysterious place called the heliopause, where scientists believe the solar wind — a stream of charged particles spewed out by the sun — fizzles out completely. Call it the cosmic doldrums, or perhaps even the heavenly horse latitudes. There are tantalizing signs that Voyager I, now some 11 billion miles from home, is nearly there. (Voyager II, which launched first, is about 2 billion miles behind its twin.)