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Tunguska to Arecibo: Connecting the Dots

Fifteen megatons of TNT would set off a blast a thousand times more powerful than the weapon used on Hiroshima. 2000 square kilometers of flattened pine forest near the Podkamennaya Tunguska River in central Siberia bear witness to what such a blast can do. That explosion occurred on June 30, 1908 [original typo said ‘2008,’ an obvious mistake!], and we’re learning more about it. The Tunguska event seems to have been an air blast occurring at an altitude between five and ten kilometers. The presumed cause: A small asteroid slamming into our atmosphere at speeds in the range of 15-30 kilometers per second.

Tunguska damage

But just how big was the asteroid? I’ve seen estimates in the range of 50-100 meters in diameter, but we know surprisingly little about the object. No fragments exist. The effects of the fireball and blast wave are apparent (and there are eyewitness accounts of hot winds and shaking buildings), but there is no crater at the epicenter of the blast. We’re left to calculate the parameters of the object through its effect and its presumed composition and speed as it entered the atmosphere.

New work at Sandia National Laboratories suggests something that is worrisome indeed. I’m going to let Sandia’s Mark Boslough deliver the bad news:

“The asteroid that caused the extensive damage was much smaller than we had thought. That such a small object can do this kind of destruction suggests that smaller asteroids are something to consider. Their smaller size indicates such collisions are not as improbable as we had believed… We should be making more efforts at detecting the smaller ones than we have till now.”

The Sandia work uses a supercomputer to match the known facts with their probable cause. The devastation delivered by the Tunguska object slammed into the ground in the form of a high-temperature jet of expanding gas. The fireball turns out to be more efficient than we realized, creating a blast wave and thermal radiation at the surface stronger than would have been predicted simply by modeling an explosion at the assumed altitude. New models of the fireball show that the energy it transported to the surface is consistent with only a three to five megaton blast, much smaller than originally thought.

So we’re looking at a smaller asteroid to account for Tunguska, which should set off a few alarm bells. For planetary security, think small. Smaller asteroids approach the Earth more frequently than the larger variety. Are we doing enough to track down not just the large potential impactors but those capable of Tunguska-like events? The question is obviously rhetorical at a time when we’re still wrangling over keeping planetary radars like Arecibo’s alive so that they can play their role in such detections. To avoid another Tunguska, we’d better get smart about not just maintaining but ramping up the asteroid search.

Comments on this entry are closed.

  • webjones December 19, 2007, 12:17

    er…. 1908?

  • Ambros December 19, 2007, 12:32

    There is a small mistake. It was June 30, 1908

  • david December 19, 2007, 12:44

    With the US and Russia each having 2500 nuclear warheads on hair-trigger alert a meteor doesn’t even have to hit to cause thousands of times the damage than a Tunguska type meteor could. There have already been dozens of close calls, making me wonder just how many close calls can we have before humanity ends itself without any outside help from the cosmos. Even the ability to track these meteors as they come in from deep space rather than having them suddenly appear on early warning systems, or as the destruction of a city, might be enough to avert a larger disaster.

    The time may be running out during which we can colonize space. I really hope that 2008 date is not being prophetic.

  • Jonah Stagner December 19, 2007, 15:16

    June 30, 2008? Typo? Very interesting post, but that date threw me for a loop, since I don’t know about the actual event being referenced and couldn’t automatically correct the date in my mind :)

  • Jonah Stagner December 19, 2007, 15:23

    Ah. I found some source material on the event, and it is indeed chilling to think that we are not doing nearly as much as we could to track such potentially devastating objects.

  • Administrator December 19, 2007, 16:00

    Thanks to all who pointed out my typo of ‘2008’ for ‘1908,’ now corrected in the article. Amazing how often you can look at a mistake and simply not see it!

  • george scaglione December 19, 2007, 16:37

    paul don’t worry for one moment i’m sure i too do that all the time! but do not forget what i always say if a large asteroid or planet killer was found to be on its way to smack us then…wow…would the manned space program accelerate!!!!!!!!!!! people would complain bitterly that NOT ENOUGH money had been spent on space thus far!! if i don’t talk to you real soon,a very very happy holiday to you and yours!!!! :) your friend george ps talk about i do it all the time,in just this simple posting i corrected myself about 5 times! lol g

  • ljk December 19, 2007, 16:52

    Though just one radioactive mushroom cloud can
    still ruin your whole day, we are down quite a bit
    from the peak of nuclear weapons on this planet,
    which happened in 1989: Between the US and USSR,
    both countries had 55,000 nuclear weapons in total.

  • Fraser Cain December 19, 2007, 17:27

    I wonder what the implications of this research are. Will astronomers need to be looking for smaller objects than planned for even the most extensive surveys?

  • Administrator December 19, 2007, 17:55

    Fraser, the answer seems to be yes, and given that we get Tunguska-like impacts every century or so, the challenge of finding these smaller objects become that much greater. My own view is that we need an NEO mission as soon as possible to start studying these objects up close and learn as much as we can about their composition. The bill sponsored by Dana Rohrabacher in 2005 called for 90 percent of NEOs 140-meters in diameter or larger to be catalogued within fifteen years. So that gives us an idea where we are, with NASA out of funding for increased NEO detection rates and Arecibo scheduled for shutdown.

  • Dryas December 19, 2007, 18:19

    Hey Paul,

    You say, “and given that we get Tunguska-like impacts every century or so,”

    Wouldn’t that prediction be based on calculations made of the frequency of enoucnters with asteroids of a given size. In other words, asteroids of size ‘X’ can be expected to cause a Tunguska class event every “x” years given the distribution and frequency of objects that size. If we lower the size of the object known to create the Tunguska event, we increase the frequency at which we can expect similar events. In other words, we could have been wrong by a significant amount and could expect these events more frequently now that the size threshhold has been lowered.

    Is that correct? I think so but would enjoy hearing from others.

  • J. R. December 20, 2007, 0:54

    Maybe NASA isn’t wording things correctly in their attempts to get support for the NEO program. My career has been in the environmental field for over 20 years. The funding spent to protect the environment over this time has increased astronomically (pardon the pun).

    Seems to me that something like this could be harmful the environment. So, maybe NASA wouldn’t have problems getting funding if they make this an environmental protection program. :)

  • James M. Essig December 20, 2007, 5:18

    Hi Folks;

    I think what ever we can do to track these enterloping asteriods would be good. All it mght take is one hit from a rock that would yield an explosion in the 300 kiloton range to be mistaken as a nuclear weapon detonating. The Cold War arsenals have been reduced but that’s not because the superpowers have become chior boys, the use of numerous moderately high yield nuclear devices is more effective than the use of a few large ones with the same total yield as the numerous lower yield devices.

    Just one large U.S. Ohio Class Ballistic Missle Nuclear Submarine can cause global havoc. Loaded with roughly 200 nuclear warheads each with the yield of anywhere from 8 to 40 times the yield of the device dropped over Hiroshima, such a submarine could set the 200 largest cities on the planet aflame after blasting flat large portions of even the largest of these cities on the planet. The ensuing poisinous smoke caused by the burning of the large variety of very dirty burning, noxious fumes emmitting plastics and other modern construction materials might just do the entire human race and perhaps animal populations in when the poisinous smoke is synergestically acting with its degrading effect on the Ozone layer coupled with the radioactive fallout that would spread througout the planet. If anything, todays nuclear warheads tend to be dirty since they rely on nuclear fission for a large part of their yield as apposed to mainly fusion for some of the big 25 megaton range metropolitan area busting hydrogen bombs deployed in large numbers by the U.S.S.R. during the hieght of the cold war.

    Perhaps instead of spending large amounts of money designing the next generations of nuclear warheads such as on the Reliable Replacement Warhead Program, we should study the fabrication of warheads large enough to knock the socks off any asteroid or comets no matter how big. Since there is no limit to the size of a fission fusion fusion bomb, one could be assembled in space large enough to destroy any incomming asteriod. Note that a stupendous 100 kilometer diameter nuclear fusion bomb having a mass of 10 EXP 15 metric tons could have a yield as high as 2 x 10 EXP 23 metric tons or the equivalent of 100 times the mass of the Earth in TNT. This is equivalent to the kinetic energy of a body with the mass of the Earth slamming into another such stationary body at about 29 kilometers/sec or about 100 times the energy needed to vaporaize a solid cold body with the mass of the Earth.

    Now, although, hopefully we will never need to produce a nuke that big, we have in theory a means for destroying any asteriod no matter how large as long as we can attack it while it is still at a safe distance from Earth.

    Obviously, other technologies can be brought to bear for diverting an asteroid such as a solar sail attached to the asteriod to slowly divert its path, mass drivers installed on the asteriod, modest sized nuclear warheads in a standoff blast to nudge the asteriod by the gases produced as a consequence of the ablative effects of the absorption of gamma rays, x rays, and fission and fusion fragments produced by the blast by the surface material layers of the asteriod, and simply attaching huge nuclear thermal or huge chemical rockets to the asteriod and driving it out of the way or at least diverting it.

    Heck if we find an unwanted potential Earth impacter, we might not want to destroy it at all but rather divert its path instead so that we can prospect for rare minerals and elements on it and perhaps use it as a study rock or laboratory for testing asteriodal mining techniques.

    That’s all for now.


  • Administrator December 20, 2007, 9:15

    Dryas, much depends upon how the calculation of a Tunguska-like object every century or so was arrived at. I’ve seen this figure in various places but don’t know what parameters were used to reach it. There is a Nature paper, about five years old, by Dick Spalding that studies satellite data on explosions in the atmosphere. I don’t have it in front of me, but let me check it to see how they translated their data into projections on the impact threat.

  • ljk December 20, 2007, 10:03

    Reducing the Risk of Human Extinction

    Penultimate draft; published in Risk Analysis 2007; 27(5):

    Jason G. Matheny

    Department of Health Policy and Management, Bloomberg
    School of Public Health, Johns Hopkins University, 624 N.
    Broadway, Room 493, Baltimore, MD 21205, USA;
    tel: 202-486-1306; jmatheny@jhsph.edu.


    In this century a number of events could extinguish humanity.
    The probability of these events may be very low, but the
    expected value of preventing them could be high, as it
    represents the value of all future human lives.

    We review the challenges to studying human extinction risks
    and, by way of example, estimate the cost effectiveness of
    preventing extinction-level asteroid impacts.

    KEY WORDS: Asteroids; catastrophic risk; cost-effectiveness
    analysis; discounting; existential risk; human extinction

    It is in html format at:


  • Edg Duveyoung December 20, 2007, 10:28

    With a much smaller rock being able to produce so much damage, it seems unwise to blow up any incoming orbs, since no matter how carefully the explosion is planned, many chunkettes of small size will be born — some of which will doubtless be heading for Earth. Better to divert objects en mass, methinks.

    Once we start mining the Helium 3 from the moon, we’ll have plenty of fuel to run any mass drivers, so no need to use dirty bombs for any purpose in space if we have nice clean H3….or so they say… All the green technologies on Earth today can be comfortably abandoned if we get the H3 steaming from the Moon like the oil ships of today stream from the Middle East.

    Has there been any research into a rocket technology that can grab the H3 as it streams from the Sun? Seems capturing H3 could fit with solar sail design. ???


  • ljk December 20, 2007, 13:48

    A spruced-up Arecibo Observatory re-opens –
    and spies an asteroid close to the sun*

    ITHACA, N.Y. — The paint is dry and it’s time for science: After
    receiving its first fresh, full coat of paint in more than 40 years,
    Cornell University’s Arecibo Observatory in Arecibo, Puerto Rico – the
    scientific actor with a title role in the James Bond film “Goldeneye” –
    made its first observation in more than six-months at 6:36 a.m.
    Saturday, Dec. 8, 2007. The Arecibo telescope spied an asteroid called
    3200 Phaethon.

    The asteroid – if it is one – travels close to the sun. But here’s the
    catch: Astronomers suspect that Phaethon may actually be a comet and a
    possible parent of the Geminid meteor shower, which annually causes many
    streams of shooting stars between now and Christmas.

    Phaethon and other asteroids that have trajectories strongly affected by
    sunlight, sun shape and general relativity effects are being studied by
    Jean-Luc Margot, Cornell assistant professor of astronomy and Jon
    Giorgini, of the NASA Jet Propulsion Laboratory, Pasadena, Calif.. Mike
    Nolan, an Arecibo staff scientist, conducted the observation.

    Asteroid orbits are influenced by the absorption and reemission of solar
    energy – or the so-called Yarkovsky effect. These changes to the
    asteroidal motion will be quantified with the Arecibo radar measurements
    to understand the properties of near-Earth asteroids. This is one of
    dozens of projects now underway at the observatory.

    Paintbrushes down: The six-month project – the first time the Arecibo
    platform and focal-point structure had received a thorough painting –
    ended in November of this year. Since then a skeletal crew of
    observatory staff worked around the clock to bring the radio telescope
    and the planetary radar back to astronomical life.

    Now, the observatory is fully functional, as all motion, electronic,
    transmitting and receiving, and computing systems are operating. “It is
    ready to return to the task of carrying out the scientific observations
    for the many thousands of hours of approved research programs that will
    keep the telescope very busy for the next several years,” said Robert
    Brown, director of the National Astronomy and Ionosphere Center, a
    national research center operated by under a cooperative agreement with
    the National Science Foundation.

    As part of Arecibo’s history, the observatory detected the first pulsar
    in a binary system in 1974, which lead to confirmation of Einstein’s
    theory of general relativity and a Nobel Prize for astronomers Russell
    Hulse and Joseph Taylor in 1993. Also, Arecibo has provided Hollywood
    filmmakers with a unique backdrop, as it was featured in the James Bond
    film “Goldeneye” and in the film “Contact,” which was based on a novel
    by the late Cornell astronomy professor Carl Sagan.

    For more news at Cornell, go to http://pressoffice.cornell.edu/

  • Administrator December 20, 2007, 14:22

    Jim, diverting an incoming impactor for potential use sounds enticing, though I think I’d rather use one of those big nukes that both you and Gregory Benford think may be necessary if we ever find ourselves staring down that particular barrel. And maybe ponder harnessing some good out of these things once we’ve learned for sure that we can divert them as needed.

  • Administrator December 20, 2007, 14:25

    Blowing asteroids into large pieces that become deadly impactors in their own right is, as you say, Edg, a major problem. Clearly this sort of thing has to be done right, and preferably with enough lead time to do the dirty work a long way from here if needed. I haven’t heard of anything re solar sail and helium-3 synergies, so you’ve given me something to dig into the literature for.

  • david December 20, 2007, 15:10

    The larger asteroids we can probably spot a long way off should we choose to invest the resources to do so. hence we would have more time and options to deflect them. The best use for thermonuclear devices in asteroid deflect would probably be for the small asteroids that are harder to spot that get past long range detection. I imagine even a gigaton range device would be enough to prevent an asteroid 100 meters in diameter from being a threat to humans.

    As for deflecting an asteroid into an earth, or lunar, orbit where it can be made use of. That is what I would do if possible with such useful object. Another option, if the orbit allows, is to deflect it so that it impacts with mars.

  • Duncan Lunan December 20, 2007, 18:34

    According to the “America at the Threshold” report (1991), mining 25 tons of He-3 from the Moon per year would meet the entire US energy demand. However on the quantities given, the strip-mined area would be the size of Tycho and visible from Earth after just two years! The same 2-year operation would give you just about enough for a manned mission to Mars or to an Eros-type asteroid.

    Uses of superconducting scoops to mine the Solar Wind for He-3 and other materials are discussed in my book “Man & the Planets” (Ashgrove Press, 1983). For really useful quantities, think 21-year missions with termini on the moons of Uranus and Jupiter slingshots for orbital plane changes.

    As regards 3-5 megatons being ‘much smaller than originally thought’, when I wrote “Man & the Stars” (1974) sources I consulted gave 1.5 MT for Tunguska, later ones doubled the figure. But the explanation then favoured for the lack of cratering was that the object was loosely structured and exploded when its height above the ground equalled its diameter, then estimated at about 3 km. In “Messages from the Stars” (1978) Ian Ridpath suggested it had been a giant fireball meteor, essentially a frosty dustball, which seems plausible to me.


  • Kevin M. December 20, 2007, 22:07

    This research dovetails with that of the Holocene Impact Group, which has found compelling evidence of mega-tsunamis from asteroid impacts on coastlines all over the world, with deposits of seafloor sediment hundreds of feet high and many miles inland. They postulate a major impact every 1000 years of so in the last 10000 years. Science is reluctantly recognizing how real and recent this threat is.

  • Edg Duveyoung December 21, 2007, 9:44


    Mars might get smacked with a cosmic kiss on Jan 30th.

    Oh boy! Fingers crossed that at least one of our cameras can get a picture for us.


  • James M. Essig December 22, 2007, 2:24

    Hi Folks;

    Imagine an asteroid with a yield of 15 megatons hitting New York City, Tokyo, Mexico City, or Bombay India. The resulting blast wave would raze to the ground essentially all structures within these cities and the resulting thermal pulse would ignite the entire remaining smashed and/or partially standing structures within the associated metro area producing a huge fire storm which could reach temperature in some locations in excess of 2,000 degrees C or 3600 degrees F thus incinerating all organic material and even melting even the strongest steels and concrete. A 25 megaton nuclear airburst by a Soviet era made metro area buster warhead would inflict fatal third degree burns by its thermal pulse of light even at a distance of 25 miles from ground zero to those exposed to the bomb light. The 15 megaton Siberian Blast meteor would be almost as powerful and because of the ensuing fire storm such an impact would cause in the metro areas of any of the above cities, say Mexico City, as many as 45 million persons could be killed from the direct effects of blast, thermal pulse and the ensuing fire storm. We definitely need to be on the lookout for these monsters. Even a modest asteriod of the one that hit Siberia would could cause horrific loss of life and potential social upheavel if it hit an ecomically integrated and advanced and technologically driven infrastructured nation like the U.S., The European Union, etc.. As for an asteriod the size of the one that took out the dinasours, we had really better be looking.


    Your Friend Jim