Voyager Golden Record Doubles as a Billion-Year Time Capsule
The Voyager Golden Record on each spacecraft carries two built-in clocks—a tiny uranium-238 sample on the cover to date its age by radioactive decay, and a pulsar map to date it via the slowdowns of 14 pulsars—providing two independent ways to estimate how long the record has drifted and offering redundancy on a timescale of hundreds of millions to billions of years.