Recently the  3.5 meter Space Surveillance Telescope located at the White Sands Missile Range in New Mexico found an an asteroid which has been named 2015 PU228. It is currently the asteroid which is most likely to collide with planet Earth in this century.  Don't worry, its closest approach to our home planet will not be untill January 15, 2081.  If there is an ideal close approaching asteroid, 2015 PU228 is it.  Humans have discovered this object long before it comes near to our home giving plenty of time to deflect it if that becomes necessary.  Serious scientific and engineering studies are currently underway to investigate various asteroid impact mitigation strategies.  These range from using a solar sail to give the problem asteroid a gentle push to setting off a buried nuclear weapon to create a rocket type thrust which will cause the potential impactor to miss planet Earth.