The Voyager Golden Record carries a small sample of uranium on its cover, placed there so that whoever finds it can measure the decay and work out how long it has been drifting — a built-in clock for a message engineered to last around a billion years.

Each of the two Voyager spacecraft, launched in 1977, carries a phonograph record. The records hold sounds and images chosen to represent Earth, assembled by a committee led by Carl Sagan. The records themselves are the part most people know about. The cover is the part worth a closer look. Electroplated onto the aluminium cover [...] The post The Voyager Golden Record carries a small sample of uranium on its cover, placed there so that whoever finds it can measure the decay and work out how lon