Researchers have found that smoke from the gun which hit Tunguska was noticed. They noticed that noctilucent clouds were formed after Space Shuttle launches dumped water vapor in the upper atmosphere. The same clouds were reported after the Tunguska impact. The Space Shuttle's water vapor is transported to polar regions within a day (it is not known how such rapid motion takes place). After the Tunguska event, the skies over Europe were bright for several nights, which the researchers believe were due to noctilucent clouds high in the atmosphere, caused by water from a comet released at Tunguska.