Reply #24: Especially given the fact that we haven't done a thorough search...

[Silent3]

...for near-earth objects, it's quite possible for a dark object on a tricky-to-observe orbit to sneak up pretty fast and catch us totally off guard, with little or no warning.

As far as I know there aren't any satellites dedicated to detecting the approach of large asteroids, just a few earthbound telescopes more dedicated to finding things that we'd have enough warning about to maybe put together a mission to do something about.

If we only had hours, or even a few days or months warning, there probably isn't anything we could do about it but go batshit crazy in the streets anyway.