In honor of Voyager 1’s 40th anniversary in space, NASA broadcast a "happy birthday" message to the now interstellar probe. NASA gave the public an opportunity to submit and vote on a tweet to be sent to humankind’s most distant spacecraft. The winning message, “we offer friendship across the stars. You are not alone," was submitted by Oliver Jenkins and announced on September 5 via NASA Television. Beamed to Voyager 1, the greeting will travel, perhaps forever, through interstellar space. At its present velocity of 38,000 MPH, Voyager 1 will reach the nearest star system in 70,000 years. Its active status will end in 2020.

Voyager 1 was launched on September 5, 1977, sixteen days after its twin, Voyager 2. The Voyager spacecraft had a primary mission of exploring Jupiter and Saturn, the largest and second-largest planets in our solar system, as well as Saturn’s rings, and the larger moons of the two gas giants. Both Voyager spacecraft had an expected lifetime of five years, but due the success of their original missions, NASA commissioned the identical probes to continue exploring our outer solar system and beyond. When their primary mission finally concluded in 1989, Voyagers 1 & 2 had observed the four outermost planets, including 48 of their moons, ring systems, and magnetic fields.

Voyager 1’s most profound moment came in 1990, when it was a mere 4 billion miles from the Sun. As part of a solar system portrait, the probe turned itself around and took a picture, capturing the Earth as nothing more than a “Pale Blue Dot,” 0.012 pixels wide. Famed astronomer and author Carl Sagan wrote of the photo in 1990, “everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives, on a mote of dust suspended in a sunbeam.” Voyager 2 remains the only spacecraft to have explored Uranus and Neptune. They are the farthest artificial objects from Earth; Voyager 1 officially left our solar system in 2013.

In addition to the tweet, Voyager 1 carries other messages for extraterrestrialswho come across Voyager 1. Onboard each probe is a Golden Record containing a collection of images, music, 55 languages, and various sounds of our home world. Designed to function as a time capsule, the Golden Record contains instructions on how to play it, and even functions as a phonograph. The covers contain a 2 cm plate of Uranium-238, half of which will decay in 4.51 billion years. This serves as an atomic clock which civilizations that encounter Voyager 1 can use to date how long ago it was launched. An engraving of the self-contained phonograph, as well as the rotation speed at which it should be played, appear on the upper left.

Carl Sagan, executive producer of the record, said “The spacecraft will be encountered and the record played only if there are advanced spacefaring civilizations in interstellar space.” Nick Sagan, Dr. Sagan’s son, is the voice behind the greeting in English: “hello from the children of the planet Earth.” The copper cover also displays a collage of star maps as well as elementary chemistry and mathematical codes.

Voyager 1 is now nearly 13 billion miles from Earth, more than 3 times the distance to Pluto. As it wanders deeper into interstellar space, humanity can only continue to wonder who, or what, will come across Voyager 1 and unlock its treasure. The Voyager mission immortalized our species and ensures that our story will still be known long after we are gone.