Notice that this was spotted by an amateur only 2 weeks before closest approach. Why was it not found by the larger installations?
One problem I like to repeat at times like this, is that these hunts for near earth asteroids look for bright spots that move against the background stars. That's a nice way to find things nearby. But any object on a collision course with earth will not be moving against the background in the days and weeks leading up to the collision when they are also the brightest and most observable. I believe this is why the ones that have exploded in the atmosphere in recent years went completely undetected. It's not just that they're small, but that they don't have the relative motion against the sky to make them stand out.
One problem I like to repeat at times like this, is that these hunts for near earth asteroids look for bright spots that move against the background stars. That's a nice way to find things nearby. But any object on a collision course with earth will not be moving against the background in the days and weeks leading up to the collision when they are also the brightest and most observable. I believe this is why the ones that have exploded in the atmosphere in recent years went completely undetected. It's not just that they're small, but that they don't have the relative motion against the sky to make them stand out.