[Anonymouse]

In fact we are overdue for a major event; they seem to occur at fairly regular intervals - 10 million years is one figure I've read.

And the reason these things aren't spotted until they're right on top of us is that a) many of them are nearly black (carbonaceous) and therefore hard to see anyway, and b) we don't have a global tracking system such as Clarke's imagined Spaceguard...and whatever the expense, we do need such a system because I for one don't believe for a moment that we'll survive anything on the scale of the event that did for the dinosaurs. The EMP alone would be devastating.

The cost of any such system will be irrelevant if we don't set it up and get annihilated as a result, don't you think?

"Important"? Hmm. Is our survival as a species important? I'd say it is - to us, at least. We've been lucky so far. Sooner or later luck always runs out.

Besides, such a system might actually pay for itself - it might spot a Near-Earth Object loaded with valuable metals. Scientists are pretty sure such objects exist.