I'm thrilled to see this article about an
experiment in shifting asteroid paths. This is the first I've heard of humans doing something that would enable them to protect the Earth from the known hazard of meteor strikes. One big hit or several medium ones would be enough to wipe out most of the life on Earth, as has happened before. We have the technology to prevent that now -- but we have to USE it. The more warning we have, the higher the chance of success, because it takes very little divergence far away to create a wide miss. The closer the rock gets, however, the more force is required to move it far enough to miss the planet. So advance warning is crucial.
Sadly people haven't put in the effort to track all the Near Earth Orbit objects. They tally those when found, but it's not rare to find a new one, so there are proabably still a lot we don't know about. Sometimes "found" means "we noticed this thing three days after it almost creamed us." There have been tracking studies, but none really comprehensive. More would be good.