As mysterious radiation spread over the Arctic and south into Europe last month, conspiracy theorists quickly claimed Russia had restarted nuclear testing at Novaya Zemlya, the Drive reports. But the truth is—probably—a lot less menacing. According to the Independent Barents Observer, a spike in the radioactive isotope Iodine-131 was first measured on the Norway-Russia border in mid-January. But the spike wasn't made public until later, when it reached France, Science Alert reports. The levels of Iodine-131 weren't high enough to be a danger to the public, but the isotope is usually connected to nuclear fission, so concern abounded. That concern only deepened when the US, with no explanation, sent its nuclear "sniffing" aircraft to Europe.
Despite the alarm, the radiation bloom probably wasn't caused by a nuclear explosion. First, there was no seismic activity to go along with the radiation spike. Second, no other radioactive isotopes spiked besides Iodine-131, Motherboard reports. And while a nuclear explosion—or accident—is still a possibility, Norway's radiation protection agency believes the likely culprit is a pharmaceutical company working with Iodine-131, which is used to treat cancers. It's still unclear where the radiation originated, with officials only narrowing it down as far as "Eastern Europe," but medical companies that work with Iodine-131 all have detectors for a leak. So it seems someone out there knows what happened but isn't talking. (Danger lurks inside nuclear facility buried under 40 feet of ice.)