Facing a Hypervelocity Asteroid Impact Disaster: To Deflect or Evacuate?

Understanding of the near-Earth asteroid impact hazard has been evolving. As larger near-Earth objects (NEOs) are retired from concern by the Spaceguard Survey, as new search strategies oriented toward short-term warning are brought on line, as we understand the increasing danger from NEOs in the 15 m to 40 m size range, and in the aftermath of the 2013 Chelyabinsk impact disaster, attention necessarily must shift toward dealing with the most likely dangerous impacts, those in the range of Chelyabinsk to Tunguska. Appropriate responses to predicted impacts by smaller NEOs involve civil defense and emergency planning endeavors. Deflection of an NEO's trajectory by spacecraft impact, or other means, is becoming a less likely type of mitigation than evacuation. We need more research on the environmental and human consequences of diverse types of hypervelocity NEOs interacting with the Earth's atmosphere, oceans, and land surfaces.