Dynamical Origin and Terrestrial Impact Flux of Large Near-Earth Asteroids

摘要

Dynamical models of the asteroid delivery from the main belt suggest that the current impact flux of diameter D > 10 km asteroids on the Earth is ;0.5–1?Gyr?1. Studies of the Near-Earth Asteroid (NEA) population find a much higher flux, with ?7 D > 10 km asteroid impacts per Gyr. Here we show that this problem is rooted in the application of impact probability of small NEAs (;1.5 Gyr?1 per object), whose population is well characterized, to large NEAs. In reality, large NEAs evolve from the main belt by different escape routes, have a different orbital distribution, and lower impact probabilities (0.8 ± 0.3 Gyr?1 per object) than small NEAs. In addition, we find that the current population of two D > 10 km NEAs (Ganymed and Eros) is a slight fluctuation over the long-term average of 1.1 ? 0.5 D > 10 km NEAs in a steady state. These results have important implications for our understanding of the occurrence of the K/T-scale impacts on the terrestrial worlds.