When the nuclear power plant in Chernobyl suffered a catastrophic meltdown in April of 1986, it took three days before the Soviet authorities admitted to what happened. And even then, it was a vague report that failed to explain the gravity of the situation. Three days of radioactive fallout spreading across the continent before Europe’s darkest fears were confirmed. And afraid they were, since countries like Norway had already measured heightened radiation levels. They knew something was up, and that the Soviets weren’t being honest.

Perhaps that’s why the press in Europe is raising the alarm on a recent spike in radiation that has been measured all over Europe. Though an unreported nuclear meltdown is out of the question, the radiation has been spreading in a similar pattern, beginning in Norway and working its way down through Western Europe, and once again raising suspicious glances towards Russia.

Iodine-131, a man-made radioactive material, is being found in small amounts across the continent. It was found in northern Norway early in January, according to officials, but has been gradually moving across the rest of Europe ever since.

But despite finding the material in January, authorities didn’t announce that it had been found until recent days. That might be because it isn’t at all clear where it has come from or how it got to be spread out.

Further information makes the find even more unusual. Iodine-131 is usually found alongside other radioactive materials, but it wasn’t. And it has a short half-life – the time required for one half of the atoms of a radioactive substance to disintegrate – but a significant amount of it was found, meaning that it is likely that it was introduced very recently.

One of the first theories to crop up, was that perhaps the Russians had conducted some kind of illegal nuclear test. But if that were the case, then the Iodine-131 would be accompanied by other radioactive materials. In any case, it’s widely believed that the radiation really is coming from somewhere in eastern Europe, given that the way it has spread is remarkably similar to the radioactive plum that was emitted from Chernobyl.

The next leading theory is that the radiation isn’t coming from a nation state at all. Since the Iodine-131 was found by itself, someone must have isolated it from other radioactive compounds. The most common reason to isolate this substance is for medical procedures. Iodine-131 is frequently used to treat cancer.

So it’s now theorized that there may have been an accidental leak from a pharmaceutical company in eastern Europe, and that unknown company has failed to report it. Because of how often wind patterns shift however, it’s impossible to determine the precise location of the leak.

Fortunately the amount of Iodine-131 that has been detected is negligible, and doesn’t pose a significant health risk. Still, the situation is so baffling that it may have convinced the US government to deploy one of their WC-135 aircrafts to Europe. The WC-135 is equipped to detected radioactive substances, and has been used to monitor nuclear tests and power plant meltdowns.

Although this situation isn’t a serious threat so far, clearly it’s serious enough that Western governments are putting their best resources on the line to figure what is really going on.