Nasa’s Deep Space Network caught a glimpse of the asteroid on Monday
An asteroid that is 400m (1,300ft) wide will pass by the Earth on Tuesday, closer to it even than the Moon.
It poses no danger to the Earth and it will be invisible to the naked eye.
Asteroid 2005 YU55’s closest approach, at a distance of 325,000km (202,000mi), will be at 23:28 GMT. It is the closest the asteroid has been in 200 years.
It is also the largest space rock fly-by the Earth has seen since 1976; the next visit by such a large asteroid will be in 2028.
The aircraft-carrier-sized asteroid is darkly coloured in visible wavelengths and nearly spherical, lazily spinning about once every 20 hours as it races through our neighbourhood of the Solar System.
It will trace a path across the whole sky through to Thursday.