For most of the time of the object's approach we would exist in a kind of cone of uncertainty. It would certainly be the most interesting few months in the history of the world. And imagine the party if it passed safely.
So how often does something like the Manson impact happen? I asked Anderson and Witzke before leaving.
Oh, about once every million years on average, said Witzke.
And remember, added Anderson, "this was a relatively minor event. Do you know how many extinctions were associated with the Manson impact?"
No idea, I replied.
None, he said, with a strange air of satisfaction. "Not one."
Of course, Witzke and Anderson added hastily and more or less in unison, there would have been terrible devastation across much of the Earth, as just described, and complete annihilation for hundreds of miles around ground zero. But life is hardy, and when the smoke cleared there were enough lucky survivors from every species that none permanently perished.
The good news, it appears, is that it takes an awful lot to extinguish a species. The bad news is that the good news can never be counted on. Worse still, it isn't actually necessary to look to space for petrifying danger. As we are about to see, Earth can provide plenty of danger of its own.