In 1977, NASA's Voyager 1 and 2 spacecraft began their pioneering journey across the solar system to visit the giant outer planets. Now, the Voyagers are hurtling through unexplored territory on their road trip beyond our solar system. Along the way, they are measuring the interstellar medium, the mysterious environment between stars that is filled with the debris from long-dead stars. NASA/ESA/G. Bacon (STScI)

Voyager 1, the Farthest-Reaching Spacecraft Ever, Marks 40 Years in Space

NASA's Voyager 1 probe lifted off on Sept. 5, 1977, and later became the first human-made object to ever break free into interstellar space.

An artist's concept of one of the NASA's twin Voyager spacecraft in space. Voyager 1 and Voyager 2 are humanity's farthest and longest-lived spacecraft, launching 40 years ago in August and September of 1977. | NASA/JPL-Caltech