That's the question Antonio Paris asked on the Aerial Phenomenon blog. Have a look - a nice graphic illustrating the difference between science and pseudoscience. Editor's note: added the image:
Antonio Paris
Space Science: New Book on the Quest to Discover ET Life and the UFO Issue
This forthcoming book by Antonio Paris looks promising: Space Science: Challenges for the Extraterrestrial Hypothesis of UFO Phenomenon. The link says that the book will “addresses what the UFO community conveniently fails to address.” For what those...