This paper examines issues related to the question of 'planetary defence', in the sense of responding to an asteroid - or any other type of Near-Earth Object (NEO) - were such a body to be detected as being on a collision-course with the Earth and predicted to cause a major disaster on impact. In particular, it engages with the implications of the possible use of nuclear weapons against an NEO.  

The first part of the paper will be 'non-legal' in nature. It aims to set the context by outlining: 1) what risks NEOs actually pose, 2) the unprecedented global political and institutional shifts towards NEO preparedness that have occurred in the last five years, 3) the recent increased scientific and political support for the 'nuclear option' in particular, and 4) the parallel developments in the nuclear disarmament and anti-space weaponisation movements that point in a very different direction.  The second part of the paper will then turn to the legal implications of using nuclear weapons against an NEO, focusing on the apparent prohibition of such action under both the 1967 Outer Space Treaty and the 1963 Partial Test-Ban Treaty. Further, possible 'defences' to illegality will be discussed.


James A. Green is Professor of Public International Law at the University of Reading, where he has been a member of staff since 2006. Currently he is also a visiting scholar at the University of Oxford, Faculty of Law (until January 2018), and previously has been a visiting scholar at the University of Michigan. James is the winner of the European Society of International Law Book Prize 2017 for The Persistent Objector Rule and International Law (OUP, 2016) and the American Society of International Law's Francis Lieber Prize 2010 for The International Court of Justice and Self-Defence in International Law (Hart, 2009). His primary research interests include the use of force (jus as bellum) and the nature of customary international law. He has published widely in leading international law journals around the world, as well as editing various book collections and contributing to others. James is the co-editor-in-chief of the Journal on the Use of Force and International Law (Routledge) and has been a member of the International Law Association's Use of Force Committee since 2010.

The PIL Discussion Group hosts a weekly speaker event and light lunch and is a key focal point for PIL@Oxford. Topics involve contemporary and challenging issues in international law. Speakers include distinguished international law practitioners, academics, and legal advisers from around the world.
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