Comment: It is a sobering thought but There is NO WAY TO TELL what might hit, and when. The world's observatories were focused on 2012 DA14 when, 6 hours before its scheduled fly-by, another large rock - from another direction - arrived out of nowhere to explode over Chelyabinsk, Russia!
The new asteroids are named 2018 CC and 2018 CB, and are between 9 and 38 meters in size. For comparison, a standard X-Wing is about 12.5 meters long, while the Space Shuttle is about 56 meters.
NASA deems any asteroid that comes within closer than 4.6 million miles of Earth to be "potentially hazardous." This might not sound close in terrestrial terminology but in terms of space distance, it's close enough to worry.
2018 CC is projected to swing past Earth today at about half the distance between the Earth and the Moon (about 120,000 miles), while 2018 CB will be much closer-about 50,000 miles. You can watch live feeds of both asteroids passing by Earth here.
Neither of these asteroids pack the punch to wipe out civilization (or a full-sized city), but they don't need to-the roughly 17-meter-wide Chelyabinsk meteor still caused hundreds of injuries just from its airburst (which exploded with the force of about 470 kilotons of TNT). The fact that these "small" asteroids keep popping up on our radar only days (or hours) before they get close means that sooner or later a near-miss will probably turn out to be a hit.
The one thing that gives us comfort is the fact that 70 percent of the Earth is covered in water, giving any wayward asteroids plenty of space to crash harmlessly (or, at worst, smite a hapless whale).
NASA has said in the past that they don't need weeks or even months to prepare for a truly devastating asteroid impact-they need decades. Nudging the rock out of its impact course or pulling it out of the way using gravitational tractor beams takes a long time. And that's just for a one-time threat-Asteroid 2015 TB145, a.k.a. the "Human Skull Asteroid," a.k.a. the "Halloween Death Asteroid," is a 640-meter-wide asteroid that keeps swinging dangerously close to Earth near Halloween.
If we should be keeping an eye on any space rock in our solar neighborhood, we're betting TB145 is the one that's going to try to kill us first.