Somewhere beyond the edge of our solar system, two small spacecraft are heading out into interstellar space. Each carries a 12-inch gold-plated copper record, a cartridge and a needle.

It's a message for anyone — or anything — that might one day find it.

The committee

In 1977, NASA asked astronomer Carl Sagan to chair a committee to decide what should go on the record. They had about a year. The record would have to explain who we are to beings who might not have ears, or eyes, or anything resembling a record player.

What's on it

Greetings in 55 languages, from ancient Akkadian to Wu Chinese. The English greeting, spoken by a child, says: "Hello from the children of planet Earth."

Sounds of Earth: wind, rain, surf, thunder, crickets, birdsong, whales, a train, a tractor, laughter, footsteps, a heartbeat — and a kiss.

Music: 27 pieces, about 90 minutes in all. Bach, Mozart, Beethoven and Stravinsky. Javanese gamelan, Peruvian panpipes, Navajo night chant, Indian raga, a Georgian choir, Senegalese percussion. Blind Willie Johnson's haunting Dark Was the Night, Cold Was the Ground. And Chuck Berry's Johnny B. Goode.

Images: 115 pictures encoded in analogue form, showing everything from DNA to supermarkets to the Golden Gate Bridge — including Ansel Adams's photograph of the Tetons.