Space Shuttle Exhaust Provides Clues to the Mysterious Tunguska Event

By Eliza Strickland | June 29, 2009 10:55 am

noctilucent cloudsAs of tomorrow, 101 years will have passed since the Tunguska Event, the mysterious explosion that flattened 800 square miles of Siberian forest. Just in time for the anniversary researchers have come up with yet another explanation for what may have caused the baffling blast. Previously, researchers best hypothesis was that a meteor struck the forest, but scientific expeditions failed to turn up an impact crater or any fragments of rock. The new hypothesis, which will be published in the journal Geophysical Research Letters, suggests that the Earth was hit by the icy core of a comet, which exploded in the atmosphere.

Researchers say that a comet strike would have released huge volumes of water vapour at very high altitude, creating highly reflective clouds that may explain why the sky was lit up for days after the collision, with people as far away as London saying that they could read newspapers outdoors at midnight, the scientists said [The Independent]. In an unusual twist, the evidence for the new theory comes from studies of the water vapor exhaust created by space shuttle launches.

Night-time or “noctilucent” clouds are the highest in the Earth’s atmosphere, forming at an altitude up to 85 km [or 53 miles]. They lead to bright night skies when they are illuminated by sunlight from beyond the horizon. Such noctilucent clouds were noted in the polar regions by researchers after launches of space shuttles Discovery in 1997 and Endeavour in 2003 [BBC News]. When a space shuttle lifts off, its main engine combines liquid oxygen and hydrogen to create about 300 tons of water vapor, which can turn into clouds of ice crystals in the upper atmosphere.

Critics of the comet theory say that ice crystal clouds that formed over Siberia couldn’t travel all the way to London by the next night, when the bright clouds were first sighted. But researcher Michael Kelley says the phenomenon could be explained by strange dynamics in the upper atmosphere. After a 2005 shuttle launch, a satellite tracked water vapour from the exhaust plume as it expanded to 1000 km across and moved 8000 km south over just a few days. Kelley believes these motions can be explained if the winds are blowing in huge eddies, thousands of kilometres across. According to [study coauthor Charles] Seyler, that could be because the atmosphere up there is somehow trapped in a thin layer, which can cause small eddies to merge and grow into larger ones. This is thought to be why Jupiter has its great red spot [New Scientist].

Kelley’s research hasn’t convinced everyone, and plenty of researchers still remain convinced that a meteor was to blame for the 1908 explosion. But Kelley’s team will continue to gather evidence, and plan to study the next space shuttle launch in July. “It’s almost like putting together a 100-year-old murder mystery” [BBC News], Kelley says.

Related Content:
80beats: The Tunguska Event: A Century Later, It’s Still Mysterious

Image: flickr / Explo

CATEGORIZED UNDER: Environment, Space
  • Jeff

    In The Cosmos: Episode 4, didn’t Carl Sagan predict it was an icy core because there was nothing left after contact? Next they’ll prove that floaters and sinkers are real, too. The man was pure genius.

  • Dennis

    Assuming metric tons, that’s 6.69 m^3 of water, which for us Americans is 1767 gallons (about half the volume of a small above-ground swimming pool).

  • limo

    Critics of the comet theory say that ice crystal clouds that formed over Siberia couldn’t travel all the way to London by the next night, when the bright clouds were first sighted.

  • Andrei Ol’khovatov

    I can add to the post by ‘limo’ that in reality according to a British astronomer report from UK some brightening of the night sky took place already on the night June 29-30! Moreover there was unusual strong skyglow in Antarctic about 7 hours BEFORE Tunguska!
    More at:

  • Steve

    Every time I see new theories or evidence on the Tunguska-event, I am perplexed that N. Tesla is never brought up in the scientific community. We know he was working on a death ray. We know that the power went out in Colorado and we know that he was trying to demonstrate that power over the North Pole. Tesla is vilified by most because of Edison’s rewriting of history but his death ray has to be taken into the conversation. Behind Max Planck and Albert Einstein, he is the third smartest person from that era! It was Tesla look into it.

  • Dennis the Mad Scientist

    re: Item 2, above- A different Dennis figures that 300 (US) tons times 2,000 (US) lb/ton equals 600,000 (US) lb. Water weighs 8.32487 lb/gal (US). 600,000 divided by 8.32487 equals 72,073.2 (US) gal. A 20 ft. by 40 ft. pool (3 ft. to 8 ft. deep) holds about 32,000 (US) gal. Therefore, one would fill about 2.25 real (US) swimming pools. Must have been the ‘metric tons’ that made it off by a factor of “40.8” (US).

  • denis alan de Shon

    What must these guys have been smoking.

    The icy core of a meteor exploding in the atmosphere indeed.

    How does that explain the trees down pattern?

    My vote is with Steve.


    Maj Den

  • http://rotojunkie Larry C

    i thought of the possibility that it was a mini-black hole that evaporated right above it…. but ahh.. a comet core sounds pretty reasonable.

  • Chubbee

    It was a methane explosion caused by release of the gas from melting permefrost.
    No, really.. I’ve recreated this phenomena right here in my own home!
    All you need is a match and some good chili.

  • Richard Woods

    At end of second paragraph, “In an usual twist …” was probably intended to be “In an unusual twist …”

  • Eliza Strickland

    Thanks for the catch, Richard, I’ve fixed that typo.

  • Sturle

    Re item 2 and 6: In the beautiful metric system 1 ton equals the mass of 1 m^3 of water (at 25 C, etc). 300 tons of water equals 300 m^3 of water. Knowing this makes your calculations a lot simpler. 1l = 1dm^3 = 1kg water.

  • Limo Hire

    Great read!


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


80beats is DISCOVER's news aggregator, weaving together the choicest tidbits from the best articles covering the day's most compelling topics.

See More

Collapse bottom bar