Asteroid Size Total Found Average Century Next Century 1–10 km ~ 920 ~ 95% 1 in 6,000 1 in 120,000 10 km + ~ 4 > 99%* 1 in 1.5 million < 1 in 150 million * Astronomers are confident that they have found all asteroids greater than 10 km across in at least 99% of the sky. Table 3.1 Progress in tracking near-Earth asteroids of two different size categories. The final two columns show the long-run average probability of an impact per century and the probability of an impact in the next hundred years (which all comes from the undiscovered asteroids).18
