[CedarDave]

Although classified as a potentially hazardous object, 2005 YU55 poses no threat of an Earth collision over at least the next 100 years.

It's the next sentence that interests me:

However, this will be the closest approach to date by an object this large that we know about in advance and an event of this type will not happen again until 2028 when asteroid (153814) 2001 WN5 will pass to within 0.6 lunar distances.

It's what we DON'T know about in advance that should worry us.

[BenLurkin]

Rumsfeld was right.