By Emma Jane Kirby
BBC News, Paris
In the US and the UK, information is released on a case-by-case basis
France's national space agency has opened its UFO files to the public by launching a website which documents reported sightings over five decades.
So many people have already tried to look at the files that it has become impossible to access the site.
France is the first country to open up fully its UFO files to the public.
Although other countries including the UK collect data on UFOs, files can be requested only on a case-by-case basis under the Freedom of Information Act.
Now, thanks to a small team of space agency researchers who call themselves the Office for the Study of Unidentified Aerospace Phenomena, the French will be able to access some 10,000 documents about UFOs, including photographs, police reports and videos sent in by witnesses.
The team offers explanations for some of the sightings - for example when 1,000 people reported seeing flashing lights in the sky one November night 17 years ago, the researchers were able to prove it had been a rocket fragment falling back into the earth's atmosphere.
But only about 9% of France's UFO cases have ever been fully explained, the group says.
And of the 1,600 cases registered since 1954, nearly a quarter are known as Category D - meaning that in spite of good data and witnesses, the mysterious sightings remain inexplicable.
The online archives will be updated whenever new cases are reported.