[echelon]

Lots of questions from a layman.

What's our level of confidence that we'll be able to find something that can wipe out cities or civilization?

What's our percentage of detection? Does it vary by size, velocity, and orbit?

How much lead time do we have? Years? Days? Hours?

What can we do about it?

Will we ever attain a complete picture of asteroids in orbit? (Assuming there are no collisions that alter trajectories?)

What's the probability we'll be hit by something big within our lifetime?

[wizzwizz4]

Answers from a layperson, while you wait for a proper answer:

1. Low, and high, respectively.

2. Almost all very big stuff, most big stuff, some medium stuff and very little small stuff, where "medium" is around the size of the Chelyabinsk one (~20m).

3. Decades for very big stuff, years for big stuff, very very variable for everything else.

4. Nothing. Plenty, in theory, but we haven't got around to setting any of it up yet. Knocking them sideways so they miss us is the current best bet, iirc.

5. No.

6. Low, assuming you're not going to live past your 90s (which is a potentially dubious assumption).