“From a purely practical perspective a comet dropping into the inner Solar System for the very first time has the potential to destroy all life on Earth with very little advanced warning, though the probability of such an occurrence is minuscule. A more likely scenario would be for the orbit of the comet to gradually evolve to the point where it collides with the Earth, thus yielding us some time to formulate a plan to divert or destroy the agent of our destruction.
“A comet’s destructive potential is related to its composition, mass and relative velocity. While the properties of its orbit will determine its relative velocity with the Earth, the mass and composition of a comet could vary over a very wide range: from a highly porous, fluffy ice ball, to a dense, water- bearing chunk of space rock.
“Ironically, the fluffy, porous ice ball will look like a huge threat as it enters the inner Solar System whereas the water-bearing space rock may be barely detectable until it is quite close and might therefore appear to be less of a problem. The collisional consequences, however, are opposite in severity.
“Understanding the range in potential properties of comets will help us to more accurately estimate the threat from any particular body and will guide our response in dealing with any potential threat. Without knowledge of a comet’s likely internal structure, formulating plans to break it up or to push it aside will suffer from being forced to anticipate a very wide range in the characteristics of such an object: pushing too hard on a small spot could break it off or bury a probe in the body of a fluffy ice-ball, while trying to blow a space rock into pieces could merely dent the surface.”
For more on comets check out issue 4 of All About Space, on sale today.