According to a Discovery Channel program I saw 2+ years ago, as of 2001 the estimates were that we had only discovered a small percentage of the NEOs (near earth objects), and that current programs would take several decades to find and map them all. The upshot of that program was that without a lot more telescopes directed skyward searching for these things, we might only get a few days' warning - certainly not enough time to develop the technology to deflect or stop something.

The impact of Shoemaker-Levy on Jupiter proved it can and almost certainly will happen. The open question is when.


Frank2135