These asteroids that graze Earth, by Michel-Alain Combes

by Michel-Alain Combes We call NEA (standing for Near-Earth Asteroids) those whose inferior perihelic distance is less than 1.30 AU (=Astronomical Unit = mean distance between the Earth and the Sun over one Earth orbit). We call PHA (for Potentially Hasardous Asteroids) those whose minimal distance to the Earth orbit (MOID) is <0.050 UA and whose absolute magnitude is (H)<22.1 (corresponding to a mean diameter of over 130m, but comprised between 100 and 200 meters according to their physical type and their albedo (this being the measure of how strongly an object reflects the light from light sources, where in most cases we are dealing with the Sun). These are the ones which we are seeking to identify and list exhaustively, in order to destroy (or deflect) them eventually, if the need should arise. As of the end of April 2010, we know of 7000 NEA and of over 1100 PHA. That is, nearly 1 NEA out of 6 is also a PHA, which is a very high percentage. (.../...) Michel-Alain Combes Biography These asteroids that graze Earth, by Michel-Alain Combes The grazian-archive website