Illustration of a Voyager probe at the Oort cloud. The two Voyager probes were launched in late 1970s. Voyager 1 has now passed into interstellar space - beyond the influence of the Sun's magnetic field - and Voyager 2 is set to do so in the early 2020s. Some 300 years from now, the probes will enter the beginnings of the Oort cloud - a swarm of inert comet nuclei surrounding the Sun up to perhaps 50,000 astronomical units from it. The cloud is so vast that the probes are expected to take around 40,000 years to pass through it into clear space.