If we knew a big one was coming in the next few years what could we do about it?
If we had a couple of years notice there are attempted diversions that could be mounted and launched in that time frame. There are discussions about different diversions on different objects — metallic versus, stone, versus blob of loose rocks.
It is the larger objects being discovered with two weeks event horizon that trouble me. If, instead, a new discovery is dead on impact course — two weeks is nothing. It isn’t only the time to mount the effort, get a craft in the right proximity, it is that the last few days of the approach takes a much larger diversion to be effective. If an object is diverted in its path by a small amount a year before it is timed to get here, a small diversion is all that is needed. A few days away, almost no diversion is enough to keep it out of the earth’s gravity well.
My understanding is that stray or long period unexpected comets are a whole ‘nother game due to greater speed of impact.