Close Encounters of Asteroids and Comets to Planets

摘要

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). We find by numerical simulations that the elongated-potato shape that is characteristic of Earth-crossing asteroids (ECAs) is likely the result of previous close tidal encounters with Earth. Some meteoroids graze the atmosphere of Earth before returning to space (at reduced speed). We used a spherical atmospheric model to study such grazers to find the condition under which they are captured into gravitationally bound orbits around Earth. We find that for about every thousand iron asteroids that hit the Earth, one is captured into a gravitational-bound orbit. Some fraction of these captured objects will have their orbits stabilized for many revolutions by tidal encounters with the Moon and the sun. We have also studied how the damage produced by such grazing and near-grazing asteroids differs from that produced by asteroids that hit Earth more directly.