A confidential Ministry of Defence report on Unidentified Flying Objects has concluded that there is no proof of alien life forms.
In spite of the secrecy surrounding the UFO study, it seems citizens of planet Earth have little to worry about.
The report, which was completed in 2000 and stamped "Secret: UK Eyes Only", has been made public for the first time.
Only a small number of copies were produced and the identity of the man who wrote it has been protected.
His findings were only made public thanks to the Freedom of Information Act, after a request by Sheffield Hallam University academic Dr David Clarke.
The four-year study - entitled Unidentified Aerial Phenomena in the UK - tackles the long-running question by UFO-spotters: "Is anyone out there?"
The answer, it seems, is "no".
The 400-page report puts it like this: "No evidence exists to suggest that the phenomena seen are hostile or under any type of control, other than that of natural physical forces."
It adds: "There is no evidence that 'solid' objects exist which could cause a collision hazard."
So if there are no such things as little green men in spaceships or flying saucers, why have so many people reported seeing them?
Well, here is the science bit.
"Evidence suggests that meteors and their well-known effects and, possibly some other less-known effects are responsible for some unidentified aerial phenomena," concludes the report.
"Considerable evidence exists to support the thesis that the events are almost certainly attributable to physical, electrical and magnetic phenomena in the atmosphere, mesosphere and ionosphere.
Meteors may have been responsible for some UFO sightings
"They appear to originate due to more than one set of weather and electrically charged conditions, and are observed so infrequently as to make them unique to the majority of observers."
People who claim to have had a "close encounter" are often difficult to persuade that they did not really see what they thought they saw. The report offers a possible medical explanation.
"The close proximity of plasma related fields can adversely affect a vehicle or person," states the report.
"Local fields of this type have been medically proven to cause responses in the temporal lobes of the human brain. These result in the observer sustaining (and later describing and retaining) his or her own vivid, but mainly incorrect, description of what is experienced."
There are, of course, other causes of UFOs - aeroplanes with particularly bright lights, stray odd-shaped balloons and strange flocks of birds, to name but a few.
Yet, it will be difficult to convince everyone that there is a rational explanation for all mysterious movements in the sky.
The report admits its findings will not persuade everyone
Some UFO-spotters believe governments will always cover up the truth about UFOs, because they are afraid of admitting that there is something beyond their control.
It is not clear how much time and effort the MoD has spent looking at the skies in recent years, but it appears there are no plans for an in-depth UFO report like the one written in 2000.
A MoD spokesperson said: "Both this study and the original "Flying Saucer Working Party" [already in public domain in the national Archives] concluded that there is insufficient evidence to indicate the presence of any genuine unidentified aerial phenomena.
"It is unlikely that we would carry out any future studies unless such evidence were to emerge."