A drastic title change may be needed for the much-awaited, new Indiana Jones movie, which comes out next month.

Harrison Ford's comeback as Steven Spielberg's swashbuckling, fedora-wearing archaeologist is to be called Indiana Jones and the Kingdom of the Crystal Skull. Judging by the spoil-sport findings of the French government's artistic research centre, revealed yesterday, a more appropriate title might be "Indiana Jones and the Heap of Old Junk".

Some secrecy surrounds the plot of the fourth movie in the Indiana Jones series, which comes out in America on 22 May. It is known, however, to be set in 1957 and has an ageing "Indy" battling Soviet agents (including Kate Blanchett) for the possession of an ancient Mayan or Aztec crystal skull. This object purportedly contains secrets brought to Earth from beyond the stars.

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Twelve such skulls, carved from solid crystal or quartz, are known to exist. Three of them are in national museum collections in Britain, the United States and France. Nine are in private hands. They have become the subject of feverish speculation by New Age writers about their purported extra-terrestrial origins. Held at a certain angle, in a certain light, it is suggested, the skulls become crystal balls which reveal the unmistakeable outline of a flying saucer.

According to one version of events, the 12 skulls – and a missing 13th sister skull – must be lined up or piled in a pyramid on or before the last day in the Mayan calendar, 21 December 2012. Otherwise the globe will fly off its axis.

Doubts about the authenticity of the skulls as Aztec or Mayan artefacts have existed for years. The British Museum, which owns one example, concluded 11 years ago that its skull had probably been polished by a wheeled machine. The pre-Colombian civilisations on the American continents discovered many things, but not the wheel. (Ah well, say the New Age theorists, the Mayans may not have had the wheel. The beings from outer space obviously did.)

The "French skull", acquired by the French state from a bankrupt collector in 1878, is now in the hands of the Musée Quai Branly, the excellent new museum of non-Western art beside the Eiffel Tower.

Because of the interest inspired by the Spielberg film, the French national museum service's research and restoration centre, C2RMF, decided a few months ago to subject the crystal skull to the most advanced forms of analysis, including "particle induced X-ray emission and Raman spectroscopy".

The centre's official report will be published next week but the principal findings were released yesterday by the Quai Branly museum. The "French skull" was probably made in a small village in southern Germany in the second half of the 19th century. The quartz from which it is made is of Alpine, not Central American, origin. The pre-Colombian origin of the "French skull", and probably several of the others, was almost certainly concocted by the French adventurer and antique merchant, Eugène Boban, who sold it to a wealthy French collector in 1875.

"The grooves and perforations [on the skull] clearly show the use of jewellery drills and other modern tools," said Yves Le Fur, the deputy head of collections at the Quai Branly. "It is inconceivable that such precision was the work of pre-Colombian artists."

The Musée du Quai Branly intends nonetheless to place its skull – only four inches tall – on special exhibition from 20 May to coincide with the appearance of the Indiana Jones film. The skull will be "hidden" in the museum and visitors will be invited to follow clues to try to locate it. French museum directors have, it seems, learnt a thing or two about spin-off tourism since the film The Da Vinci Code. The directors of the Louvre were, initially, aghast at the absurd and wilful errors made in Dan Brown's best-selling thriller and the subsequent film. They later relented and arranged Da Vinci Code tours of the museum.

Doubts about the authenticity of Aztec or Mayan crystal skulls have recently been posted on archaeology.org, the website of the Archeological Institute of America. Jane MacLaren Walsh, an anthropologist at the Smithsonian Institution in Washington and a leading authority on pre-Colombian art, traces the strange history of the skulls and the legends which have come to surround them.

The largest of the skulls, almost 10 inches high, larger than a human head, was sent anonymously to the Smithsonian in 1992. The disturbing, milky-white sculpture came with an unsigned letter. "This Aztec crystal skull ... was purchased in Mexico in 1960. I am offering it to the Smithsonian without consideration," it said.

"Crystal skulls have undergone serious scholarly scrutiny, but they also excite the popular imagination because they seem so mysterious," Ms Walsh says. "Some believe the skulls are the handiwork of the Maya or Aztecs, but they have also become the subject of constant discussion on occult websites. Some insist that they originated on a sunken continent or in a far-away galaxy. They are intensely loved today by a large coterie of ageing hippies and New Age devotees."

Ms Walsh points the initial finger of blame at Boban. Several allegedly Mexican crystal skulls turned up in Europe after France intervened in the Mexican civil war in 1863 to install Maximilian von Hapsburg as emperor. Two skulls were exhibited by Boban at the Exposition Universelle in Paris in 1867 after he served as the ill-fated Maximilian's official archaeologist.

Boban went to Mexico as a teenager and learned Spanish and the Aztec language, Nahuatl. He seems to have had a genuine passion for pre-Colombian history and culture but he also had to make a living. He opened an antiquities business in Paris, which is known to have mingled genuine artefacts with the dubious and the downright fake. He later moved his business to New York.

The celebrated Manhattan jewellers Tiffany and Co bought an "Aztec" crystal skull from Boban for $950 in 1881. The British Museum purchased it a decade later at the same price. This skull remains in the museum's collections in Bloomsbury but is now presented as being "probably" a fake.

Enter another generation of experts, fakers or fantasists, this time British. In 1934, Sidney Burney, a London art dealer, bought a crystal skull almost identical to the one in the British Museum. In 1943, it was sold through Sotheby's to the British explorer and writer Frederick Arthur Mitchell-Hedges. He later claimed to have discovered the skull at a Mayan site in Belize (then British Guyana). In his autobiography, Danger My Ally, in 1954, he said that the skull was "at least 3,600 years old and according to legend was used by the High Priest of the Maya when performing esoteric rites. It is said that, when he willed death with the help of the skull, death invariably followed."

The object, sometimes called the Skull of Doom, was owned for 60 years by his daughter, Anna Mitchell-Hodges, until her death last year. She sometimes charged a fee to look at it.

The Skull of Doom is an especial favourite with New Age theorists. It is said to glow with a blue light and to crash any computer hard drive which comes near to it. One of the New Age skull theories holds that the skulls are, in all probability, an very advanced form of extra-terrestrial computer.

"Although nearly all of the crystal skulls have at times been identified as Aztec, Toltec, Mixtec or occasionally Maya, they do not reflect the artistic or stylistic characteristics of any of these cultures," Ms Walsh, the Smithsonian anthropologist, points out. She believes that some of the earlier skulls were faked in Mexico in the 19th century. Others probably came from Europe. The "Skull of Doom" was probably a fake of one of these fakes.

Her findings tally almost exactly with those of the French museums' research centre, C2RMF. This agency, run by the Louvre, establishes the identity of disputed art works and explores old artistic techniques. It is regarded as the most advanced organisation of its kind in the world.

The centre states "with a reasonable degree of certainty" that the "French" skull at the Quai Branly and the "British" skull in the British Museum came from the village of Idar-Oberstein in southern Germany. The village is known to have specialised in making similar objects as bases for crucifixes in the period 1867 to 1886. This would explain why the "French" skull has identical-sized holes at top and bottom.

Analysis of the quartz used in the skull has identified the material as of Alpine origin. The British Museum skull is believed to have used Brazilian quartz. From the Alps or Brazil to Mexico by flying saucer is just a short hop, all the same. Could extra-terrestrial makers of the skulls not have shared the same skills as 19th-century German artisans? We will probably never know.

Legends surrounding crystal skulls have become a staple subject of science fiction novels and video games, as well as New Age theories about the extra-terrestrial history of mankind.

A central legend, according to the Quai Branly, goes as follows. The 12 known skulls represent the 12 "worlds", or planets, which were once inhabited by mankind. Of these, the planet Earth, was the youngest. The "Itzas", the ancient people from other planets, brought the skulls to Earth to convey their knowledge to humans. A 13th skull was manufactured on Earth and all were kept in a great pyramid by successive civilisations in Central America, the Olmecs, the Mayas and finally the Aztecs, who foolishly lost or dispersed them.

Some aspect of this legend will provide the plot for the new movie. It seems that Spielberg, the director, and Ford, the star, had severe doubts about mystic, crystal skulls as the story line for the new Indiana Jones story, the first to appear since 1989. One of the reasons for the long delay, according to Hollywood gossip, is that Spielberg and Ford hated the skulls idea, put forward by George Star Wars Lucas, who wrote the script. But after a dozen re-writes, they were brought around.

Will the new findings of French artistic scientists send Spielberg and Ford into a fit of despair? Hardly. The previous Indiana Jones movies were far from historical documentaries but they were amongst the most popular adventure films ever made.

The success of The Da Vinci Code suggests that it takes more than a few inconvenient facts to spoil a good story. "In one sense these are enchanted objects, even if they are fakes," said Yves Le Fur of the Musée Quai Branly. "No doubt the Indiana Jones film will generate a whole new series of legends."