TNT equivalent
where "N" (&gt;"D") is the expected number of objects larger than a diameter of "D" meters to hit Earth in a year. This is based on observations of bright meteors seen from the ground and space, combined with surveys of near-Earth asteroids. Above in diameter, the predicted rate is somewhat higher, with a asteroid (one teraton TNT equivalent) every couple of million years — about 10 times as often as the power-law extrapolation would predict.