"Maybe the big take-home point on this one is it's a pretty big object and it was only found 10 or 12 days before closest approach,"
I've said this before. The way they find these things is looking for movement against the distant background / starfield. That works pretty well for finding things, but there is one problem. Any object on a collision course with earth will NOT be moving across the background in the days leading up to the collision. It will appear stationary against the stars, so will not be detected by these systems. To some extent it also doesn't matter that we are orbiting the sun because while near, earth and asteroid will be in the same accelerating reference frame.
Another way to model it is to think of firing a projectile from earth into deep space and see how that tracks against the background. That'd be the reverse scenario and there will be no relative motion until it's far enough to not get the same influence from the sun.
I've said this before. The way they find these things is looking for movement against the distant background / starfield. That works pretty well for finding things, but there is one problem. Any object on a collision course with earth will NOT be moving across the background in the days leading up to the collision. It will appear stationary against the stars, so will not be detected by these systems. To some extent it also doesn't matter that we are orbiting the sun because while near, earth and asteroid will be in the same accelerating reference frame.
Another way to model it is to think of firing a projectile from earth into deep space and see how that tracks against the background. That'd be the reverse scenario and there will be no relative motion until it's far enough to not get the same influence from the sun.