The Chelyabinsk meteor is the most important impact event after the Tunguska event, almost 100 years before. The object that entered Earth on February 15, 2013, was a small-sized Apollo asteroid (with a diameter of 17-20m), and caused serious damages. This fact proves according to the authors that the number of Potential Hazardous Asteroids (PHA) are almost double that what is thought, although most of them (with diameters smaller than 100m) are not capable of global damage but can cause severe local damages. They state also the fact that the approaching direction was from the Sun side, which is a totally blind spot currently at the existing optical surveys.
