The Tunguska Event of 1908 has fascinated astronomers, UFO hunters and many others for the past century. What caused the explosion that flattened over 800 square miles of Siberian forest?
Was it a meteorite impact? Or was it an exploding alien spaceship?
Personally I have always favoured the cometary hypothesis: that the explosion was caused as the nucleus of a comet collided with the earth and broke up in the atmosphere. Recently Michael Kelley et al. of Cornell have offered further evidence in favour of this hypothesis. They argue that the noctilucent clouds visible for several nights after the event and as far away as Britain are consistent with the presence of water vapour due to the break up of a comet. (See ‘A Mystery Solved’.)