NASA's twin Voyager space probes launched 40 years ago.

A gold-plated record and cover that NASA attached to Voyager 1 and Voyager 2 contains sounds, pictures, and text from Earth in case aliens ever find the spacecraft.

The golden records are designed to keep their data intact for a billion years — longer than humanity will likely exist.

About 1 billion years from now, the sun will begin to boil Earth's oceans, then later 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 about life on Earth — a basic human catalog that aliens might one day discover and decode.

The mission is now detailed in a remarkable PBS documentary called "The Farthest", which premiered on August 23 and will re-air on September 13 at 10 p.m. ET.

"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 Voyager as the farthest, fastest, and longest-lived space mission, but also one of humanity's greatest endeavors.