As shown here, asteroids (and comets) may be very different than our expectations. Accordingly, the scenarios we develop to mitigate against hazardous asteroids and comets must take into account their unknown physical properties. Mechanisms capable of deflecting solid coherent objects may not work on a rubble pile. For example, the explosion of an implanted nuclear device on a rubble pile, the deflection scheme used in the movies ``Deep Impact'' and ``Armageddon'', may instead disperse it into an dangerous cloud of debris. The maximum amount of explosive energy capable moving a rubble pile without disrupting it is unknown; without detailed information obtained from an extensive in situ study, we could easily use a bomb orders of magnitude too big or too small. Moreover, producing and stockpiling such weapons is arguably a greater immediate threat to human life than that represented by killer asteroids.
Like most projects, it is important to choose the right tool for the job; a hammer might be a good tool to move a brick, but it is a bad tool for moving a pile of marbles. A better asteroid diversion technique may involve a series of small impulses which act over a long period of time. Melosh et al. (1994) has suggested several non-nuclear strategies for producing these impulses, some of which present only moderate engineering challenges. For example, Melosh et al. has suggested that focussed sunlight, reflected from one or many solar collectors, could be used to vaporize material on the surface of a asteroid. The recoil of the asteroid from the vapor plume would create a small sustainable thrust which, within a year or so, could deflect it away from Earth. The system, which is big, slow, and fragile, cannot be easily be misused as a weapon, while it can safely move rubble piles and solid objects alike. Thus, there may be more than one way to move an asteroid; it is only prudent to investigate all of the possibilites
It is safe to say that the public awareness to dangerous asteroids will grow commensurably as near-Earth asteroid detections become more frequent (e.g., the media frenzy surrounding the discovery of near-Earth asteroid 1997 XF11). Unfortunately, without a clear understanding of the facts or the physical evidence, movies, television shows, and news reports discussing the hazard to Earth from impacting bodies, however well-intentioned, are bound to be misleading, such that the public will be misinformed. For these reasons, it is important that we not only continue to increase our knowledge about asteroids but that we communicate this information to the public in a way that is readily accessible to everyone.