A team of scientists hopes to crack one of the layers of mystery surrounding 15th-century French heroine Joan of Arc: Could a rib and other fragments recovered after she was burned at the stake be hers?

Eighteen experts plan a battery of tests to determine whether the few remains reportedly recovered from the pyre where the 19-year-old was burned alive for heresy — including a rib bone and some skin — really could have belonged to her.

The woman warrior-turned-saint remains omnipresent in the French imagination, nearly 600 years after her ashes were thought to have been thrown into the Seine River.

The tests, which will take six months, will not be able to say with certainty that the remains are Joan of Arc's, because there is no known DNA sample from her to compare them with, said Dr. Philippe Charlier of the Raymond-Poincare Hospital in Garches, west of Paris.

But the analyses will determine with "absolute certitude" if the remains could not be hers, Charlier said at a news conference.

He said Joan of Arc supposedly was burned three times on May 30, 1431, following her trial in the Norman town of Rouen.

She initially died of smoke inhalation, according to Charlier, and when she was burned a second time, her internal organs were not fully consumed by the flames. Nothing was said to remain after the third cremation except her ashes.

The 6-inch rib bone was wrapped in a blackish substance and was "remarkably well-preserved," Charlier said.

He said scientists would use DNA testing to determine whether the rib belonged to a woman. Then they will put it through other tests to determine its exact age.

No DNA comparison can be done with possible descendants, since Joan of Arc's supposed family tree is "probably false," he said.

Joan of Arc was tried for heresy and witchcraft and burned at the stake after leading the French to several victories over the English during the Hundred Years' War, notably in Orleans, south of Paris.

The illiterate farm girl from Lorraine in eastern France disguised herself as a man in her campaigns and said she heard voices from a trio of saints telling her to deliver France from the English.

Joan of Arc was beatified in 1909 and made a saint in 1920.

The supposed remains were gathered by an unidentified person and conserved by an apothecary until 1867, when they were turned over to the archdiocese of Tours.

In 1909, scientists declared it "highly probable" that the remains were Joan of Arc's. Given recent developments in genetic technology, the researchers at Garches decided to try again.

This will not be the first time Charlier has dabbled in the uncertainties of France's past.

Last year, he was able to identify the cause of death of Agnes Sorel, the official mistress of the 15th century King Charles VII, as mercury poisoning. But he was unable to determine whether the poisoning was a murder.