A password will be emailed to you.

A popular news story doing the rounds this week is this Space.com item about how recent space shuttle launches may have solved the mystery of what hit Tunguska in 1908: a comet. Key to the new theory are ‘noctilucent clouds‘, which were seen over Europe in the days following the explosion, and the fact that these clouds are also created by the Space Shuttle on take-off:

About 97 percent of the exhaust from a shuttle launch turns into water, a by-product of the liquid hydrogen and liquid oxygen fuel. A single shuttle flight pumps 300 metric tons of water vapor into the Earth’s thermosphere, and the water particles have been found to travel to the Arctic and Antarctic regions.

Noctilucent clouds were tied to the launch of Endeavour (STS-118) on Aug. 8, 2007. And high-altitude clouds were detected over Antarctica shortly after the fateful launch of Columbia, which along with its crew was lost during re-entry. Columbia’s plume was 650 miles long and 2 miles wide and reached Antarctica in three days.

Cornell University engineering professor Michael Kelley figured the bright night skies after the Tunguska event must have been the result of noctilucent clouds. And since they require water vapor, Kelley assumed a comet was the culprit.

It’s worth noting though that for the theory to work, a completely “new model of upper-atmospheric physics is needed” to explain how the water vapour traveled so far. Given that rather large leap, I found it quite ironic that the Space.com article begins by ridiculing the ‘UFO theory’ for Tunguska, then proceeds to explain how a spaceship leaving the Earth shows that the event was caused by a comet. Funny stuff.

For those looking to read the original paper, it can be found in Geophysical Research Letter, and is titled “Two-dimensional turbulence, space shuttle plume transport in the thermosphere, and a possible relation to the Great Siberian Impact Event.”