In 1977, NASA launched two Voyager spacecraft into the sky with the initial goal of exploring the outer solar system. Once the spacecraft had examined Jupiter, Saturn, Uranus, and Neptune, they kept flying for billions of miles, ultimately entering interstellar space. Each carried a copy of the Golden Record, a disc of earthly sounds that are intended to represent humanity to any extraterrestrial civilizations that might encounter it. (To date, the record is the only human-made object to have left the solar system.) Astronomer Carl Sagan chaired the committee that determined the disc’s contents, which include booms of thunder, chirping birds, and snippets of more than 55 human languages. There’s also a lot of music: Compositions by Bach, Beethoven, and Mozart made the cut, as did those by blues legend Blind Willie Johnson, Azerbaijani folk singers, and rock ’n’ roll pioneer Chuck Berry.