TERRESTRIAL IMPACT RATES FOR THE KNOWN POPULATION OF EARTH-CROSSING ASTEROIDS

摘要

Impact probabilities on the Earth are calculated for all known asteroids using terrestrial eccentricities of 0.0 (circular heliocentric orbit), 0.0167 (the present value) and 0.0579 (the maximum value attained as our orbit evolves). Although the latter eccentricity leads to a greater number of asteroids having Earth-crossing orbits (i.e. present-day Amors having perihelia within 1.06 AU, plus presumably a yet-undiscovered population with aphelia currently just within our orbit), it is found that the impact rate is largely unaffected: the increase in the population selected is compensated by a decrease in the individual collision probabilities. Mean impact probabilities are also derived as a function of the asteroid size, or limiting magnitude. As is to be expected, the smaller objects have higher impact probabilities than the larger ones, due to discovery selection effects. Similarly the impact speeds are lower for the smaller asteroids because these selection effects lead to low-eccentricity, low-inclination orbits near Earth being favoured.