1In the late nineteen seventies, two small spacecraft left the Earth and began an extraordinary journey toward the edge of the solar system and beyond.
2The twin Voyager probes were designed from the very beginning to explore the giant outer planets and then report their discoveries back to Earth.
3Using a rare alignment of the planets that occurs only once in many generations, they swung gracefully from one giant world to the next.
4Each careful gravity assist from a passing planet flung them a little faster and a little farther toward the distant edge of the solar system.
5Along the way, their cameras revealed erupting volcanoes on the moon Io, the thick orange haze of Titan, and the intricate shining rings around Saturn.
6After completing their planetary mission with spectacular success, the two probes simply kept travelling onward into the cold and empty darkness beyond Neptune.
7Decades after their launch, both spacecraft have finally crossed the boundary of the Sun's influence and entered the space between the stars.
8Attached to the side of each spacecraft is a golden record, a carefully prepared message in a bottle for whoever might one day find it.
9The record carries friendly greetings spoken in dozens of human languages, together with music and natural sounds chosen from many different cultures around the world.
10It also holds more than a hundred photographs showing blue oceans, busy cities, wild animals, growing children, and the smiling faces of ordinary people.
11Long after their batteries finally fail, the probes will continue to drift silently through the galaxy for many millions of years to come.
12And long after our own civilisation has changed beyond all recognition, that small golden message from Earth will quietly endure among the stars.