Abstract

Current planetary defense policy prioritizes a probability assessment of risk of Earth impact by an asteroid or a comet in the planning of detection and mitigation strategies and in setting the levels of urgency and budgeting to operationalize them. The result has been a focus on asteroids of Tunguska size, which could destroy a city or a region, since this is the most likely sort of object we would need to defend against. However a complete risk assessment would consider not only the probability of an impact but also the magnitude of its consequences, which in the case of an object of Chicxulub size could be the end of civilization or even human extinction. This paper argues that a planetary defense policy based on a complete (or one could say genuine) risk assessment would justify expenditures much higher than at present.