And now it's gone

As expected, the asteroid 2006 HZ51, discovered last Thursday, has already been removed from the potentially hazardous objects list. It was taken down just after noon today, after additional observations ruled out any possibility of impact.
That's the outcome everyone expected, of course, as I explained in my original posting (below). It has now been moved over to the "list of removed objects" page. All 165 of its possible impact dates have now been ruled out.
But, as I said then, what was interesting about this case, as with so many objects that come and go from the list, is that it helps to focus our thinking about the whole issue of possible impacts, and often a newly-discovered object has interesting, unique features that illustrate different aspects of how we might respond to a real threat. In this case, the fact that there was a potential impact so soon -- just over two years away -- highlighted just how unprepared the world still is today for such a threat. If there had been a real risk, there would have been almost nothing we could do about it, with so little lead time. That underscores the importance of thinking ahead, planning, and doing the necessary research and testing so that we might have a way to respond, even to a short-term hazard (although two years would be a tough one, even with much greater advance preparation).
Anyway, once again the planet is safe for now. Phew.