I remember reading about the Iridium impact and I thought it seemed strange. I know that the US tracks thousands and thousands of bits of orbital debris. How could the collision of two satellites be a surprise to them?

I was listening to some aerospace guy on the radio a few months back. He was mentioning that we've entered a new era of hazardous space debris. Before, stuff that fell off boosters and such would create a finite amount of debris that needed to be tracked. But we've gotten to the point where there is enough junk out there that they occasionally collide with other junk, thereby creating a lot MORE debris which is harder to track since they are now much smaller pieces. The problem is only going to get worse over time as more chunks collide with other chunks.

I'm not sure how long it would take for gravity to pull these very small bits of debris out of orbit, if at all.