Nine Billion Miles

NASA's two extraordinary Voyager spacecraft are now pushing through the edge of our Solar System-- a turbulent region of magnetic bubbles-- and heading into interstellar space. They will be the first manmade objects to leave the Sun's domain.

In numerical terms, the edge of the Solar System turns out to be roughly 9 billion miles away. That's yet one more fact the Voyagers have established. In an odd coincidence, according to projections, by mid-century the human population of Earth will be about 9 billion. By that time, the Voyagers may have reached true interstellar space.