NEARLY 18 billion kilometres away, for the first time in the history of the universe, a human-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 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 16 kilometres 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, humankind, via its mechanical representatives, is becoming a species of interstellar explorers.

When Voyager launched, it was not known whether a single planet existed outside our solar system: now 786 have been found.

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.

Telegraph, London