Plausibility is a very interesting word. Imagine that someone tells you that a group of individuals are planning a bank robbery. Since you find this plausible, probably you will advice your friend to go to the police as soon as possible. The imaginary episode tells us a very important thing about conspiracies. Usually the plausibility of a conspiracy grows when a small group of people is involved. Watergate is one of those real conspiracies. We find that a relatively small group of individuals is involved and also we learn that there was someone who revealed this conspiracy to the press. Warranted conspiracy theories tend to be small in scope requiring only a small group and are relatively easy to cover up. However, bigger conspiracies have smaller plausibility, because the cover up is more difficult if not impossible. So, if you read that there is a conspiracy to make you believe that in Mars there is no intelligent life, trees, big animals and terrestrial bases, you will see the obvious: the whole world scientific establishment must conspire to keep the “real” Mars situation secret. Thousands of astronomers, scientists, technicians, authorities and employees are forced to lie to the public and even to their families and friends. This is of course impossible and the plausibility of such a giant conspiracy is cero. The more people who are or must be in the know, the less likely it is that the conspiracy will remain secret, and the more certain it becomes that the absence of any leak is indicative that the conspiracy does not exist. Of course the same thing can be said about the presumed cover up of contacts between authorities and extraterrestrials. Paradoxically, conspiracy theorists are forced to make their imaginary conspiracies bigger and bigger. RationalWiki suggests the following questions to detect the plausibility of any conspiracy theory. 1 - How many people are part of this conspiracy? Are there enough of them to carry out the plan? What infrastructure and resources does it need? How much time and money did it take and where did this money come from? (For instance, the idea that the Nazi themselves set the Reichstag fire would only require handful of men and minimal amount of money to pull off while something like the moon landing hoax would require tens of thousands if not more to carry out; the rock samples alone might require a decade to falsify and filming would take an airtight soundstage orders of magnitude larger than any known vacuum chamber). 2 - Explicitly who gains what from the conspiracy and for what price? Is this the easiest way of gaining it? If not, why was it chosen over the easiest way? If it is an old conspiracy — who gains what from maintaining it? 3- How large is the supposed conspiracy and how likely is it to be covered up if has gone on a long time? If there are thousands of conspirators, and the conspiracy has gone on for decades, why have none been defected? Why have none of them leaked the story? If many conspirators are dead, why have none of them told the truth on their deathbeds, or in their wills? (It should be noted that with government-based conspiracy theories one can have issues with the fact there are things about WWI, nearly 100 years ago, that are still classified and therefore unknown to the general public, nullifying these types of questions even with a skeptic - however, these involve what might be termed "rigidly defined areas of doubt and uncertainty" and usually there is significant supporting evidence from other sources). 4 - If there are many thousands of conspirators, how are they organized? Where are the secret conferences held? How do they keep track of membership? If they are organized through known channels or entities, how do they keep non-members who work there from uncovering the conspiracy? 5 -There are many intelligence agencies associated with rival nations, with the ability to expose secrets. If, say, the US government is running a global conspiracy, why have the French, Russian, or Chinese intelligence agencies never revealed it, to cause a major scandal in the United States (If all intelligence agencies are involved, see #2)? If they have, when and where did they do so? 6- Does belief in this theory require accepting that the conspiring entities are incredibly competent, bone stupid, organized and clever, and hopelessly incompetent -- all at the same time?[31] 7 -More generally, what if any implausible contradictions does this theory depend upon? A secret well and carefully kept by extremely powerful and aggressive entities, that one or (especially) more "bozos on the bus" happens to know all about, and talk about openly, including on the Web, without being disappeared?http://rationalwiki.org/wiki/Conspiracy_theory#Questions_to_ask_about_a_conspiracy_theory