By Rob Waugh
Last updated at 3:50 PM on 28th February 2012
It is 460ft wide and soaring through space - on a possible collision course with Earth.
Nasa has identified a new asteroid threat to our planet and calculated that it could potentially impact on February 5th 2040.
The 2011 AG5 has already attracted the concern of the UN Action Team on near-Earth objects, which has begun discussing ways to divert it.
They have put the odds of it hitting us at one in 625, though that could change nearer the time.
Were the rock to land on a city it could cause millions of deaths, although mankind would live through it.
The asteroid which wiped out the dinosaurs 65 million years ago was nine miles wide, compared to 460ft for the 2011 AG5.