In September 2013, NASA boffins declared that the Voyager 1 probe had finally crossed into interstellar space. The unmanned spacecraft was launched in 1977 to study the outer planets and has now made history by becoming the first man-made object to leave the solar system. It's momentous news, but not as surprising as when scientists announced several days later that the craft had unexpectedly reversed its trajectory and was now heading back towards the Earth at double the speed.
"We don't quite know what it's found out there to make it act so unexpectedly," said mission leader Ed Crevice. "There are a number of possible scenarios but we still have a lot of data to analyse. One thing we can say, however, is that whatever the reason for Voyager's odd behaviour, it's safe to assume that something has certainly put the wind up it."