An asteroid called 2012 DA14 will narrowly miss Earth as it flies past at 7pm tonight.
The 45 metre diameter rock is big enough to destroy London.
It has no chance of hitting, but it will enter the orbit of more than 100 satellites.
It is expected to fly 17,200 miles (27,000 kilometres) above Earth's surface at around 7pm GMT.
The flyby of 2012 DA14 is the closest-ever predicted approach to Earth for an object this large.
More top news
Events company Secret Cinema is planning to screen a film in protest at what they have called the 'censorship' of The Interview.
Sepp Blatter's £19 million attempt to immortalise Fifa on screen could do with a sequel. How about The Untouchables or The Usual Suspects?
Some of the children at the Royal Free Hospital in London were less than impressed with their visit from Alex Oxlade-Chamberlain.