“Too late” to do what? Launch a space shuttle with a nuke to detonate on it?
An expert on a news story I heard said it would take a warning period of months, not hours or a day, to stop a deadly asteroid strike.
Congress many times dragged its feet on this (and also strengthening the shielding of the power grid) and has left us helpless. The impact would cool off the world and kill us slowly and set off riots for food,water and medical care.
Someday within the next 20 years, scientists say, the likelihood of a major disastrous strike against the Earth is 100% for practical mathematical purposes. Like, will the northeast US have a major freeze and heavy snow in the next year—yes.
We have no practical system worked out but it could entail bumping the object to move it off course or landing on it to propel it somewhere. Blowing it up would set off big fragments hitting somewhere.
The last time the asteroids came to earth with the one mile dia (est) rock, it ended the ice age; 1000 years later the next one mile dia (est) struck it brought on the Younger Dryas - colder than the ice age temps.
Search for “the Carolina Bays” and read “Magicians of the Gods”.
These rocks are thew remnants of a broken up comet. Usually we pass thru the part of the torus with the small stuff which make a nice shower. But once in a while we pass thru where the big stuff lives and they are civilization-enders and real climate changers.
No, nukes only make more pieces which hit more targets - all you an do is find a successful way to move the rock so it does not cross earth’s orbit.This presupposes you have already not only detected the rock, but calculated its actual orbit and crossing time - one miscalculation and the jig is up.