A 400m-wide asteroid is passing by the Earth on Tuesday and will be closest to us just before midnight.
The strangely-named rock 2005 YU55 will come within 202,000 miles of Earth - but that's closer than the Moon.
It's the largest space rock fly-past since 1976 and the next one won't be til 2028.
But we won't even be able to see it with our eyes. It can only be seen with telescopes.
Experts say anyone with a telescope larger than 15cm diameter might be able to see it.
Space scientists in California and the Caribbean island of Puerto Rico will be tracking 'radio echoes' of the asteroid as it passes by, so they can get more information about it.
Equipment at Nasa, the American space agency, has created the radar image above.
Nasa experts have reassured the public that the asteroid will not hit the Earth.