Planetary Defense: Near-Earth Objects, Nuclear Weapons, and International Law

The risk of a large Near-Earth Object (NEO), such as an asteroid, colliding with the Earth is low, but the consequences of that risk manifesting could be catastrophic. Recent years have witnessed an unprecedented increase in global political will in relation to NEO preparedness, following the meteoroid impact in Chelyabinsk, Russia in 2013. There also has been an increased focus amongst states on the possibility of using nuclear detonation, in particular, as a means of diverting or destroying a collision-course NEO, something that a majority of scientific opinion now appears to view as representing humanity’s best—or perhaps only—option in extreme cases. Concurrently, recent developments in nuclear disarmament and the de-militarization of space are in direct contradiction to the proposed “nuclear option” for planetary defense. In the context of the significant developments that have occurred in relation to NEO impact risk over the last five years, this article analyses the question of whether a nuclear NEO response would (or could) be permissible under international law. Potential restrictions and prohibitions under treaty law are assessed, as are a range of mechanisms that may act to preclude possible illegality. The article concludes by advancing a tentative proposal for a move towards (strictly limited and safeguarded) legal preparedness