The origin of the Tunguska blast a century ago has never been solved.

The explosion near the Podkamennaya Tunguska River on June 30, 1908 flattened some 500,000 acres of Siberian forest. An eyewitness described flashes and thunder and everything (including their hut) flattered completely by a strong wind.

No one knows what caused it, but a long-standing theory is the crash of an asteroid or comet.

But other interesting theories abound.

Struck by the similarity of Tunguska and Hiroshima decades later, Alexander Kazantsev, a popular science fiction writer, wrote a story in which the Tunguska blast was the exploding nuclear power plant of a spaceship from Mars. Russian scientists took up the cause and claimed to find various bits of evidence–never proved–for a UFO crash.

Another theory is the Nikola Tesla “death ray.” The man who pioneered radio and modern alternating currents claimed to have invented a device that could transmit energy over huge distances.

The story goes that Tesla tested it the evening of June 30, 1908. He aimed the death ray towards the Arctic and turned it on. At this time, Robert Peary was trekking to the North Pole and Tesla asked him to look out for any unusual disturbances.  Tesla then watched the newspapers and sent telegrams to Peary, but didn’t hear about anything unusual in the Arctic.

But Telsa did hear the news about an unexplainable event in Siberia. He was thankful no one was killed, as it was clear to him his death ray had overshot its target. He then dismantled the machine, saying it was too dangerous to keep. Tesla claimed the plans for the death ray were stolen from his hotel room in the 1940s.