Eleven billion miles away, for the first time in the history of the universe, a man-made object is about to leave our solar system.
Voyager 1 set off on the longest journey ever taken on May 5 1977. In the 34 years, nine months and 24 days that it has been travelling, it has shot by Jupiter and Saturn, photographing the giant planets and their moons; it has passed the Kuiper belt, the vast cloud of asteroids that lies past the orbit of Neptune; it took the first “family portrait” of the planets, showing Earth as one more bright point in the black – a pale blue dot among the others.
Now, hurtling silently on at more than 10 miles a second, it is reaching the edge of the heliosheath – the final layer of the heliosphere, the bubble of charged particles surrounding our Sun that marks the limit of the solar system. Its mission, investigating the gas giants, ended 30 years ago, but as the old machine moved closer to the outside universe it was given new goals, of studying the edge of the solar system and the space beyond. Its instruments have started to shut down, as its nuclear power sources slowly deplete, but its radio transmitter is expected to keep running until at least 2025, reporting back what it finds: it is so far away that those signals now take 16 hours to arrive. At last, mankind, via its mechanical representatives, is becoming a species of interstellar explorers.
The fear, though, is that Voyager – impossibly ancient in technological terms – represents the high-water mark of humanity’s cosmic ambition. It was launched in the late phase of the Cold War-driven space race, the scramble for national prestige that led America to put men on another world. Reading Sixties science fiction, you can feel the excitement: just as the Wright brothers and Bleriot’s achievements heralded an age of air travel, it was expected that those boots on the Moon would lead us to conquer space. But in the three years after Neil Armstrong and Buzz Aldrin, another 10 men went to our nearest neighbour – and then we stopped. We kept going into space, but only just: if the world were the size of a football, no one would have gone more than about half an inch from the surface in the past 40 years. We gave up, the accusation goes. We chickened out.
But that’s not fair. This is a golden age of space exploration. We might not see men in space suits stepping on alien worlds, but every day we learn about the universe in ways that earlier scientists could only imagine. In a few weeks, the Curiosity rover, the largest and most complicated robot ever sent to another planet, will arrive on Mars, to search for signs of life. The Cassini probe has sent back terabytes of data from the moons of Saturn: they would be the most beautiful space images ever taken, were the Hubble telescope not filling Nasa’s hard drives with glorious pictures of nebulae and galaxies. When Voyager launched, it was not known whether a single planet existed outside our solar system: now 786 have been found, the bulk of them by the Kepler telescope. Japan has sent a spaceship called Ikaros, powered by a solar sail, to Venus; China is building its own space station, and recently sent its first female astronaut into orbit. We might not be landing humans on Mars, but we don’t need to: we know more about the universe than ever before, and are learning more all the time.
In 40,000 years, Voyager, long dead and silent, will pass near a star in the Camelopardalis constellation. Hopefully humans will have walked on more worlds by then. But right now, the heirs to Magellan and Marco Polo are robots, and they’re doing extraordinary things.