An asteroid the size of a house is set to pass close to the Earth today (12).
The space rock will hurtle past our planet at a distance of about 42,000km, bringing it within the Moon's orbit and just above the altitude of communication satellites.
Nasa scientists say there is no risk of an impact, but the flyby does provide them with the opportunity to test their asteroid-warning systems.
A global network of telescopes will be closely monitoring the object.