What should we do if a 'planet-killer' asteroid takes aim at Earth?

Jan 16, 2020
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I'm kind of surprised there's no mention at all of how long it would take to implement the various responses - there's just a few vague mentions about it: if we have more time, we can do Type 1, or if time gets too short, no response works. How much more time does Type 1 take compared to Type 0? What's the minimum cut-off time before there's nothing we can do? Yes, we're likely to have plenty of advance warning if we spot a "planet killer," but assembling a payload, mounting it in a rocket, testing it and finally launching it is not exactly something we can do in a day, either.