On Nuking Menacing Asteroids

Introduction: Most scientists now accept that impacts on the earth of large asteroids and comets have occurred in the past, and will, without intervention , occur again; with devastating affects on the earth and all living creatures. About ten years ago, researchers [1,2] and others studied a number of ways that an asteroid could be diverted from an impending collision with the earth by pushing it sufficiently to change its course, making it miss the earth. Among the methods suggested, it is generally accepted that with a short warning time, such as a few years, only the nuclear bomb approach would work. In [3] I report some recent studies on these issues, including the effect of asteroid porosity which is now thought to be likely. One of the conclusions is that porosity can make the use of surface explosives or impacts of large masses, both methods that deflect by cratering, ineffective. Of the other cases, some of the more interesting conclusions deal with the mitigation methods using a standoff nuclear weapon, which I present here. Deflection by standoff nuclear detonations: The standoff method uses a nuclear weapon detonated at some height above the asteroid surface, resulting in a large deposition of x-ray or neutron energy into a surface layer of the asteroid. The neutrons penetrate further so generally give more effect than the x-rays. Therefore I assume a weapon designed for a significant neutron yield. Both [1] and [2] consider this method. Both obtain estimates of the impulse imparted to the asteroid by estimating a blow-off velocity and a total blow-off mass. A more precise result is obtained by an analysis of the wave dynamics of the processes, which I obtained using a one-dimensional wave propagation code and the ANEOS three phase equation of state for the response of the asteroid material. I consider both porous and non-porous materials. I use the ANEOS model for Quartz given in [5]. For the porous case, the Herrmann p-alpha model is added to the underlying EOS for quartz. The p-alpha model is characterized by three material properties. The distension ratio α is the porous mass density divided by the mass density of the particulate solid material. The pressure P e is a pressure at which crush begins, and P s the pressure at which all voids are crushed out. There is a curve of distension v. pressure defined by these three parameters. To …