Meteoroid, Not Comet, Explains the 1908 Tunguska Fireball

By Breanna Draxler | July 1, 2013 2:10 pm
Trees blown down by the meteor that struck near Russia's Tunguska river in 1908.

Damage from the 1908 Tunguska impact as documented by Leonid Kulik on his 1929 expedition to the epicenter.

On this day 105 years ago, Russians were reeling from the enormous fireball that streaked through the sky the day before and flattened almost 800 square miles of trees near the Podkamennaya Tunguska River.

It wasn’t a bird. It wasn’t a plane. And it sure as heck wasn’t Superman. But whatever it was, scientists found no trace of it in the charred rubble. It has taken researchers over a century to identify the extraterrestrial object—but in a recent paper, geoscientists revealed that the culprit was indeed a meteoroid.

The Hundred-Year Mystery

The burning chunk of rock struck Siberia on June 30, 1908 with a force 1,000 times more powerful than the atomic bomb dropped on Hiroshima. Over a century later, it is still the largest impact event in Earth’s recorded history. The area was uninhabited (luckily) but that did not mean the blazing ball of who-knows-what went unnoticed.

Scientific expeditions over the last century have combed the site and proposed a flurry of hypotheses: some said meteoroid; some said comet. The comet hypothesis was gaining traction by mid-century since such a mass of ice and dust would have vaporized when it hit the Earth’s atmosphere, causing an explosion without leaving any physical trace. But with so little evidence to go on, none of the theories could be proven.

A 1978 expedition came closer when it uncovered minuscule mineral samples embedded in peat at the epicenter of the blast. Researchers determined the samples to be 99.5 percent carbon with inclusions of other trace elements such as troilite and iridium. The amount of pressure required to form such samples suggested that the minerals were contained in a meteorite that smacked into the Earth. But these samples could also have formed when the heat and pressure of the space blast encountered rocks right here on our home planet, so the results were deemed inconclusive.

Mineral sample from the Tunguska meteorite of 1908.

Zooming in on the structure and composition of the Tunguska mineral samples. Image courtesy of Kvasnytsya et al./Planetary and Space Science

Taking a Closer Look

Armed with new and improved scanning technology, a group of geologists from Europe and North America decided to resurrect these mineral samples from their archive in the Ukrainian Academy of Sciences. They analyzed the samples with traditional microscopy techniques, mass spectrometry and high-powered X-rays—techniques that have been developed and refined in the past few decades—to give a much more detailed view, and published their findings in Planetary and Space Science in May.

While the carbon components of the samples weren’t necessarily from out of this world, the iridium concentration was ten times higher than in Earth rocks. The researchers were able to look at the surface structure and chemical composition of the samples in detail to determine that the mineral samples gathered at Tunguska most likely represent tiny bits of an iron meteorite. They suggest that the structure is the result of rapid cooling after an impact, and report that the mix of minerals matched those of other confirmed iron meteorites, like the one found in Arizona.

So it looks like the case is closed, just in time for Tunguska to blow out the candles on its 105th carbon-studded birthday cake. Let’s just try to keep the fire under control this time.

CATEGORIZED UNDER: Environment, top posts
  • wandering_j

    Has anyone said anything about the size? Or did I just overlook it somehow?

    • Bobareeno

      Size? Do a Google search and find out. I’m sure someone has a conspiracy theory about it. And don’t forget……size DOES matter…..

    • http://blogs.discovermagazine.com Michael Woolfolk

      You could calculate the size from the energy release?

      • Brian Epps

        Not necessarily. As velocity increases, so does relative mass. A
        meteor the size of a pea could destroy the world if it were moving fast
        enough.

    • coreyspowell

      Current estimates are that the meteor was a stony-iron asteroid about 50 meters wide. The size estimate depends on the velocity, composition, and models of how the blast wave traveled.

  • Jeff

    I wish that space aliens would land on earth in an advanced space craft and help us get out of this ecological mess we have gotten ourselves in. There has to be a non polluting form of enery that we ignorant humans have not thought of yet somewhere.

    • Rachel LaUlu

      there are sooo many forms of natural energy and it could all be given out for free with our technology… it’s greed that keeps us in the dark ages – we the people are the 99% that work with 1% of the money – we can change things on planet earth – stop asking for aliens and be the change!

    • http://blogs.discovermagazine.com Ian Ward

      What if the aliens came because they messed up their home planet?

    • Virtuous2012

      Arthur C. Clarke’s book “Childhood’s End” proposes an extra-territorial invasion by a benign forced called “The Overlords”.

      I re-read this book every few years with growing appreciation.

      Its message is what Earth becomes in its “golden age” when everybody has everything they want — and people have no more drive or ambition; just lapsing into luxury and comfort.

      The Overlords bring a benign form of “dictatorship” … but I will say no more ..read for yourselves.

      Happy 4th to all. Not just barbeque and beer…teach your children what this day means.

    • http://blogs.discovermagazine.com Michael Keener

      EASY: In full sun, you can safely assume about 100 watts of solar energy per
      square foot. If you assume 12 hours of sun per day, this equates to
      438,000 watt-hours per square foot per year. Based on 27,878,400 square
      feet per square mile, sunlight bestows a whopping 12.2 trillion
      watt-hours per square mile per year.
      An ASTOUNDING amount of energy falls on earth everyday, we just have to figure out how to use it…which should be every scientist/engineers goal… and every government on the planet..

      • Edward Royce

        Then the clouds come in, it rains and nothing works because there isn’t any sun. Good luck with that. C.f. UK during winter.

      • Nick

        just to let you know, the cost to do what you are imagining would be on the order of 12 trillion every 30 years. And you would have to dump 5-6 trillion of perfectly good power plants to do that. And all that cost would go to china. So good luck with that.

  • DKG’s Spam Feed

    What caused the radiation? Or does that not matter?

    • http://blogs.discovermagazine.com Ian Ward

      Probably the iridium.

    • philw1776

      What radiation? Big rocks will emit some brief X-Rays from the plasma generated by re-entry heating.

  • Nosca Khalid

    The area of destruction is so mind-boggling wide; the
    meteoroid had to be huge and for it to leave no big chunks of left-over is
    still a mystery. The meteorite that recently fell over Russia although minute
    in comparison left a trail of scattered pieces.
    Where is/are the bodies of evidence? If there are any; Scientists and curious
    scavengers would have found it in the last 105 years.

    • http://blogs.discovermagazine.com Ian Ward

      The higher the energy of impact, the higher the % of meteoroid mass that gets vaporized?

    • Tom Billings

      Dr John Lewis ran the numbers on your question 30 years ago. The forces on the body of the meteorite, and its pieces as it breaks up, go up with the 3rd power of the speed. That means that a body hitting the atmosphere at over about 20-25 kilometers per second will be torn apart even if it’s solid Iron.

      Then E=(1/2)m X V(^2) takes over, describing the energy involved. At 25 kilometers per second, the meteorite has 62 times more kinetic energy per kilogram than a kilogram of TNT does in chemical potential energy. That is way more than what is needed to vaporize the fragments once it is torn apart. In a way, the atmosphere is a shield against the *fastest* bodies hitting the ground, and burns up the smallest ones, but the intermediate speed larger bodies get through with devastating force far worse than Tunguska, such as at Meteor Crater, or worse at Chixilub.

  • colindenronden

    E=½mv*2. So you either have to know the mass or the speed.

  • antoine clarke

    “Iron meteorite”? Fancy name for a giant bullet.

  • TruthTeller

    No aliens? No Bigfoot? Tunguska’s no fun.

  • georgedixon1

    The Democrat National Committee, along with President Obama, has concluded that Republicans caused the meteor to impact when it did, but, they assert that the intended target was a city.

    • gtwreck

      It was not at all the Democrat Lite AKA Republicans. It was just President Obama’s original Scape Goat Bush.

    • coreyspowell

      I believe you two are in the wrong forum. This one is about science.

    • Janice S. Roberts

      like Mike explained I am inspired that someone can make $7794 in one month on the computer. have you read this site link w­w­w.K­E­P­2.c­o­m

  • MattLohr

    Iridium shmiridium. Everybody knows it was the biggest interdimensional cross-rip prior to 1984.

    • H_Canáhmoac

      Dr. Raymond “Ray” Stantz, Ph.D. was correct in this assertion and Dr. Peter Venkman and Dr. Egon Spengler agreed. Science by consensus.

  • John Robinson

    It’s stuff shooting down from outer space, what difference does it make in the long run?

    (P.S. Troilite is not an element, and I don’t think this study is nearly as conclusive as you spin it here.)

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