Risk assessment for asteroid impact threat scenarios

Asteroid impacts can cause a wide range of damage through multiple potential hazards, from localized blast waves or thermal radiation, to tsunami inundation, to global climatic effects. The level of risk posed by these hazards depends not only upon their extent and severity, but also upon the likelihood of the various damage ranges. Some consequences may be more moderate but very likely, while others may be unlikely but catastrophic. Evaluating the risk from these hazards involves substantial uncertainties across all aspects of the problem, including the properties of the asteroid, the specifics of its entry, and the complex high-energy damage physics involved. NASA's Asteroid Threat Assessment Project (ATAP) performs Probabilistic Asteroid Impact Risk (PAIR) assessments that use fast-running entry and hazard models to evaluate millions of impact cases representing the distributions of these many uncertain parameters. This paper presents the current PAIR modeling tools and approaches used for evaluating specific asteroid impact threat cases. We give an overview of the current PAIR model used to support hypothetical impact threat scenarios and discuss some of the key applications of these assessment in supporting planetary defense response and preparedness. We then present the results and key findings from the recent 2023 PDC hypothetical impact exercise as an example of the primary types of risk results and metrics being developed to inform potential mitigation and response decisions. The 2023 PDC scenario represents an impact threat from a large 800-m asteroid with an initial uncertain size range from similar to 150 m to 2 km in diameter, spanning sizes that would cause only local damage to sizes that could potentially cause tsunamis or global effects. Results demonstrate key assessment and response challenges for such large impact scenarios, and motivate the need for further modeling and simulation studies to better understand the potential onset and severity of regional and global-scale hazards.