A hundred years ago yesterday a comet or an asteroid or a divine wild pitch crashed into the Tunguska region of central Siberia with a force 1,000 times greater than the atom bomb dropped on Hiroshima. People hundreds of miles of away felt the blast, and the resulting embers in the atmosphere illuminated the night sky over London. Very cool, and very fortunate that practically no form of civilization existed at or around the epicenter (Indiana Jones would have needed, like, a whole subzero fridge to survive the blast). But the trouble was that, apart from charring and stripping the forest trees and otherwise heating up the joint, the flaming object left no crater. Even if it had, it'd have entered the cultural consciousness as the early 20th-century precursor of crop circles and grassy knolls. "Tunguska" has led to all manner of interesting theories as to what really happened, the lamest being that aliens did it. Here are a few of the better ones:

1. The Earth Mother awakens. Thomas Pynchon's novel Against the Day had it that a North Pole expedition roused some terrestrial geological entity that, upon being shipped to Siberia, lost its shit and unleashed Gehenna up top as payback for being moved from the Arctic tundra.

2. The zap and whoops. Italian Serbo-Croatian inventor and coil namesake Nikola Tesla fired a death ray that went to eleven and evidently worked a lot better than the still-implausible human Xerox machine David Bowie cobbled together as him in the film The Prestige. Best captured in the book Callahan's Key by Spider Robinson, who could argue anything with that name, as far as I'm concerned.

3. The underground cosmic event. The Jackson-Ryan hypothesis: Tunguska was caused by a teensy subterranean black hole that one day decided to pucker or burp or whatever. See Larry Niven's The Borderland of Sol for how that works.

4. The Ruskies and spacetime. In yet another fiction, Chekhov's Journey, Ian Watson posits that the Soviets invented a time-ship that they lost a handle on. This enables Anton Chekhov, who must have sounded like a patient out of Ward 6, to learn of the impending the cataclysm in 1890, almost two decades before it occurred.

[BBC]