The biggest mystery in Europe this year isn't "The Da Vinci Code"--it's the question of what is killing the Continent's great pipe organs. That is the issue confounding scientists, music historians and organ experts involved with the EU-funded Corrosion of Lead and Lead-Tin Alloys of Organ Pipes in Europe (COLLAPSE), a research project formed when a mysterious corrosion began appearing in the hollow cylinders of some of Europe's oldest and most venerable instruments. One of the first incidents was discovered in the early 1990s, when the pipes of the 538-year-old Stellwagen organ of the St. Jakobi parish church in Lubeck, Germany, became cracked and hole-ridden. Since then, similar cases have appeared from Italy to the Netherlands. Experts fear that thousands of Europe's 10,000 historic organs are damaged.

There are many theories as to what lies behind the deterioration. One likely cause is corrosion by acids that are emitted naturally from oak wood, which was used to renovate many organs in the 1970s. Others suspect it might have something to do with the pipes' low tin levels. Researchers are also weighing the effects of temperature, humidity and outside emissions.

As of now, the only way to save the affected organs is to replace the damaged pipes with new ones. But this presents another problem. "These pipes are like the Stradivarius violins," explains COLLAPSE's Carl Johan Bergsten. "No one knows how the organ builders back then made them sound so beautiful." Like the corrosion affecting the instruments today, he says, "it's a mystery."