Estimating the NEO Population and Impact Risk: Past, Present and Future . ... Since most of the risk resides in the largest impactors, finding that fraction of the largest bodies, and that none of them has a significant chance of impacting in the next century or so, "retires" more than 90 % of the impact risk, including most of the risk of a globally catastrophic impact event. ... In the mid-size range, from ~150 m to ~1 km, the main risk is from tsunami generated by an ocean impact. ...