Why NASA's twin Voyagers probes are the most important spacecraft ever launched - and could be the last evidence of humanity's existence

About 1 billion years from now, the sun will begin to die, blow off its outer atmosphere, and engulf our tiny planet in hot plasma.

Luckily, the galaxy will have NASA's twin Voyager spacecraft to remember us by.

The two nuclear-powered probes launched 40 years ago and became the first and only robots to take close-up photographs of Uranus and Neptune, the planets' moons and rings, and other objects in the outer solar system.

The Voyagers also carried with them a golden record of sounds, images, and other information life on Earth - a basic human catalog that aliens might one day discover and decode.

The mission is now detailed in a remarkable detail for PBS documentary called "The Farthest", which premiered on August 23 and will re-air on September 5 (the date of Voyager 1's launch).

"Fifty years from now, Voyager will be the science project of the 20th century," Brad Smith, a Voyager imaging scientist, said in the movie.

Here's why many scientists and engineers not only hail the Voyagers as the farthest, fastest, and longest-lived space mission, but also one of humanity's greatest endeavors.