It is alleged that several species of extraterrestrial origin have visited our planet in the past or continue to visit today; and, in some conspiracy claptrap, are walking amongst us in disguise, are collaborating with select government factions, and have even created a human-extraterrestrial hybrid to gradually populate earth with their species. Why they are here, if that is the case, is beyond the scope of this book–for our purpose is only to investigate whether or not they can exist.