News on yesterday’s BBC website brings us closer to a pivotal moment in human history. We are going to leave home.

There have of course been many homes, and so many departures. This one will be less obvious than many others. When Sputnik broadcast its beeps from above the atmosphere of Earth on 4th October 1957, it was apparent that something had changed forever. It’s possible to draw a direct line from the fear that little sound engendered in the US to the achievement of the Apollo lunar landings. Humans walking on the Moon was another departure – as images from the Lunar Reconnaissance Orbiter reveal, there are tiny marks to show that we have stood upon another rocky planet.
Now, emissaries from the human world are leaving the Solar System. The threshold they cross is wide.
These emissaries are the two Voyager spacecraft. Launched in August and September 1977, these two probes were designed for a five-year working life but, 35 years on, are still transmitting. Voyager One is 11 billion miles from earth, its tiny signal taking 16 hours to reach the Deep Space Network array. Its twin sister Voyager 2 is a little closer. At about 40,000 mph, they are crossing the evanescent boundary where the power of the Sun comes to an end. It is a search for what is not there to see, but there are ways of measuring the Sun’s decline out there – earlier in the year, instruments of Voyager 1 suggested that the solar wind was no longer dominating the spacecraft’s environment, and as a consequence it is now detecting many more of the particles thrown out by exploding stars. Some time over the next three years or so, the two craft will puncture the outermost rim of the Solar System and enter deep space.
Where nothing made by human hands has ever gone before. Where the messages from the Voyagers will be detectable, just, until their plutonium power sources fail. Where they will, in the words of Timothy Ferris in a recent article in The Smithsonian sent to me by my cousin Austin, ‘wander forever among the stars, mute as ghost ships but with a story to tell.’ Voyager 2 will pass within 1.7 light years of the red dwarf star Ross 248 in about 40,000 years. Voyager is not expected to get closer than 2 light years to the star AC+79388 in about the same time. Both stars would be seen, were anything still looking by then, to grow gradually in brightness and then fade.
Not exactly a close encounter. But the Voyagers, though deaf and blind, might yet speak. They are famously fitted with gold-plated copper records, created by Carl Sagan and others as a chiselled record of the world from which they came. Like the records of earliest humans carved into caves and onto rocks, these LPs will last for at least a billion years before micrometorites erode their grooves. Time enough, perhaps, for something or someone to decode them.
What do they say? The records hold 118 images from Earth and greetings in 54 languages. There is some music and recordings of natural sounds like whale and birdsong. This is who we are and where we live, they say, the whole of the Earth summarises in analogue. In case you are concerned, instructions on how to use of the records are etched into the housing.
The Voyagers are a huge achievement. There is a book to be written – perhaps one day I will – about how they have changed the our understanding of our place in the cosmos. They tell the story of a revolution as profound as that which began when telescopes extended human sight beyond its natural limits. They are the furthest outreaching of our fingers. We are soon to touch emptiness for the first time.
In the meantime, the Voyagers teach us the scale of things. This composite image was taken on 14 February 1990, Valentine's Day, from a distance of approximately 4,000,000,000 miles away by the cameras on Voyager 1. The Sun is the bright object marked S while Earth is, in Carl Sagan's phrase, a pale blue dot.

Sagan went on to say:
‘From this distant vantage point, the Earth might not seem of any particular interest. But for us, it's different. Look again at that dot. That's here, that's home, that's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, ...every superstar, every supreme leader, every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam.’