It wiped out 2,150 square kilometers of forest, has left meteorologists stumped for more than a century and been the subject of a role playing mystery on Nintendo’s Wii and DS. Now, 105 years after the Tunguska Event in Siberia, Andrei Zlobin of the Russian Academy of Sciences’ Vernadsky State Geological Museum claims to have found the first and only clue to what caused the impact. And as it turns out, it’s been sitting in his lab, unnoticed, for the past two decades.
According to his paper on the find, published at arXiv.org, Zlobin picked up stone samples from the bottom of Khushmo River on his way back from an unsuccessful field research trip to the Suslov depression in 1988, an area where much of the damage at Tunguska is visible. He had dug a series of holes in the permafrost, looking for potential meteorite or comet fragments at depths of 1908 soil levels, but to no avail. On his way back he collected around 100 stones from the riverbed, but failed to examine them until 2008.
When he finally studied them, Zlobin found that three of those stones exhibited signs of melting (one has a particularly glass-like surface with bubbles). They also feature regmalypts on their surface — fractures that occur when meteorites soar at great speeds towards Earth, causing fragments to vaporise off as atmospheric gases rip around them. Although the impact of the hit is estimated to have been 1,000 times more powerful that the Hiroshima bomb, the heat of the impact is not thought to have been hot enough to melt any rocks on Earth’s surface (according to samples taken from trees affected in the area). Hence, Zlobin is claiming the rocks exhibit all the markers of being meteorite fragments. He does, however also assert that the density of whatever hit Tunguska (about 0.6g per cubic centimetre) matches up with density measurements of Halley’s comet’s nucleus, so a comet has not been ruled out.
Although Zlobin admits there is plenty more work to be done — chemical and isotopic analysis is needed to find out what’s going on inside the three rocks — it’s an interesting find. Tunguska has left the scientific community stumped for over a century for several reasons. Although it’s presumed the impact was the work of a comet or meteorite (some argue an alien being…), the blast occurred in an incredibly remote area of Siberia that was uninhabited and not explored until 1927, when meteorologist Leonid Kulik ventured into the field. He did not unearth any evidence (there were accounts of him finding a similarly glassy stone, but it was lost), and more importantly he was unable to find any evidence of a crater, as has no one since.
Zlobin’s find will certainly reignite interest in the mystery, but he’s created one of his own in the process. Why would someone who has dedicated much of their career to investigating Tunguska wait more than two decades to study stones retrieved from the area?