Just Look Up: Planetary Defense*

Of the many and increasing natural disasters that humans face on planet Earth, an asteroid impact is one cataclysmic event that can be completely averted with current technology and enough warning. Planetary Defense is a growing global campaign to identify potentially hazardous asteroids or comets, develop possible mitigation missions, and establish emergency response protocols if a mission fails. Though almost all extinction-size asteroids have been located, many smaller Near-Earth Objects (NEOs) remain undiscovered and could pose a threat. If an NEO is found to be on a collision course with Earth, depending on the length of warning time, there are multiple mission options to prevent a disaster. In an ideal scenario, with decades of notice, the recently-tested kinetic impactor mission is the preferred and most developed choice. However, a wide range of threat scenarios exist, especially in instances of short warning times, where a kinetic impactor would be insufficient to prevent disaster. In such cases, an alternate option is deploying a nuclear device to the NEO. Despite delivering the most energy per kg of launch mass, the effectiveness of a nuclear mitigation mission is highly dependent on the NEO's physical properties, such as size, shape, mass, composition, and structure. All these attributes may be either poorly constrained or completely unknown before a mission is launched and unlike a kinetic impactor, a nuclear mission cannot be tested beforehand. Thus, high-fidelity and efficient simulations of an NEO's response to the radiation a nuclear device emits (neutrons, gammas, and x rays) are essential for exploring the uncertainties of this mission-type. This talk will give an overview of Planetary Defense, show how a nuclear mitigation mission might be implemented, and highlight recent simulation advances using nuclear data-informed energy depositions to model an attempted asteroid deflection or disruption.