The asteroid that wiped out the dinosaurs 65 million years ago measured about 10 kilometers wide, but any impactor larger than 1 kilometer wide could trigger catastrophic climate change. “We are practicing for the real serious case.” 
 
 Many scientists believe the Earth will once again be hit by a space rock of the size that wiped out the dinosaurs, though nobody knows when. With a one-in-750 chance of hitting the planet then, TC4 is listed at number 13 on the “risk list” of objects posing even the remotest impact risk. The 2013 Chelyabinsk meteor, which injured nearly 1,500 people in the Russian city, was about the size of 2012 TC4.
– The Earth will be having a close call—astronomically speaking—when a 65-foot-wide asteroid buzzes past on Thursday, the Christian Science Monitor reports. According to AFP, asteroid 2012 TC4 will come within 27,000 miles of Earth—about one-eighth the distance between the Earth and moon and about 5,000 miles above most of the satellites orbiting Earth. There's no chance the asteroid will hit the Earth, but its proximity will be used to test an asteroid warning system. 2012 TC4 will make further passes by Earth in 2050 and 2079, and there is a chance it could make impact on the latter fly-by. "Things do hit other things, and we’re not special in that regard,” the associate director of the International Astronomical Union tells the Monitor. The asteroid is at No. 13 on the "risk list" of objects that could impact Earth.