Scientists at Cornell University have finally confirmed the source of a mysterious explosion that levelled 2,000 sq. km of Siberian forest in 1908, showing it was almost certainly caused by a comet entering the Earth’s atmosphere. “It’s almost like putting together a 100-year-old murder mystery,” said lead researcher Michael Kelley, noting that previous theories had ranged from comets to meteors. “The evidence is pretty strong that the Earth was hit by a comet in 1908.” Reports say that after the explosion, called the Tunguska Event, the skies shone brightly for several days over Europe. His team concluded those bright skies were the result of noctilucent clouds—night visible clouds made of ice particles, the highest in the Earth’s atmosphere—created by the massive amount of water vapour spread by the comet’s icy core, caught in swirling eddies that caused the clouds to form thousands of kilometres away. Scientists are working to understand how the water vapor travelled so far without scattering, which conventional physics would predict. “There is a mean transport of this material for tens of thousands of kilometres in a very short time, and there is no model that predicts that,” Kelley said. “It’s totally new and unexpected physics.” They believe it’s related to counter-rotating eddies with extreme energy; once the water vapor got caught in these, it could travel close to 300 feet per second.