"The more measurements made of the object's position over time, the better we can predict its future path. In most cases, the new measurements mean the object can be removed from the risk list because the uncertainties in the orbital path are reduced and the possibility of impact is ruled out.”
While the chances of a major asteroid hitting Earth are small – NASA believes there is a one in 300,000 chance every year that a space rock which could cause regional damage will hit – the devastating prospect is not impossible.
Plans - Go - Earth - Strikes - NASA
However, there are some plans on the go which could help Earth against potential asteroid strikes. NASA is currently studying...