So by now, everybody has read about the meteor which broke up over the Chelyabinsk Oblast late last week. The reportage on it was pretty interesting in the beginning — a lot of between-the-lines skepticism was being put out there by American news outlets. I was a little wary myself, too, as a lot of the initial reports from Russia were pretty sketchy, buffeted primarily by Russian dashboard cameras, which, in our Photoshop and AfterEffects age, are probably not at the top of our list of “reliable sources.” For people who care about Cold War science and technology, of course, there’s the additional fact that ChelyabinskOblast is a major site for secret Russian military-industrial developments. It’d be like reports of suspicious explosions around the Nevada Test Site, or Los Alamos, or Pantex. Chelyabinsk Oblast is the home of Chelyabinsk-70, the Soviet Livermore, and just north of it is the city of Sverdlovsk (now Yekaterinburg), the site of a 1979 anthrax leak that the Soviets tried to cover up by claiming it was something more “natural” in origins. Add in the legacy of the Soviet response to Chernobyl, the relative rarity of this sort of meteor strike — once a century is the frequency that’s been cited — and the extreme rarity of something like this happening over inhabited land — most of the planet is devoid of human occupation — and some skepticism in the absence of solid evidence was, I think, not unwarranted. Eyebrows raised, including mine, but apparently it all checks out.
Some of the Russian nuclear weapons facilities near the meteor path. Via Hans M. Kristensen, FAS: “The odds of a meteor hitting one of these nuclear weapons production or storage site are probably infinitely small, but on a cosmic scale it got pretty close.”
How powerful was the explosion? NASA currently is saying it is the equivalent of a 500 kiloton blast, which is a lot. 500 kilotons is (as you can see) half a megaton, is about the upper-limit of a pure-fission nuclear weapon, and is, as journalists love to breathlessly relate, some 20-30 times the power of the bombs that hit Hiroshima and Nagasaki. That the only result was a lot of injuries caused by windows blowing inward — something that occurs with a shock wave of one pound per square inch or above — is attributed to the fact that the meteor exploded many miles above the ground, away from the city.
Personally, I cast a dubious eyeball towards the comparisons of natural phenomena with nuclear weapon energy releases. It’s an incredibly common trope, though. Wikipedia’s coverage of the 2004 Indian Ocean earthquake is actually quite reflective of how this gets talked about, even if it is somewhat dorkier in its citation of units than the average journalistic account:
The energy released on the Earth’s surface only (ME, which is the seismic potential for damage) by the 2004 Indian Ocean earthquake and tsunami was estimated at 1.1×1017 joules, or 26 megatons of TNT. This energy is equivalent to over 1500 times that of the Hiroshima atomic bomb, but less than that of Tsar Bomba, the largest nuclear weapon ever detonated. However, the total work done MW (and thus energy) by this quake was 4.0×1022 joules (4.0×1029 ergs), the vast majority underground. This is over 360,000 times more than its ME, equivalent to 9,600 gigatons of TNT equivalent (550 million times that of Hiroshima) or about 370 years of energy use in the United States at 2005 levels of 1.08×1020 J.
Lots of numbers thrown around, lots of energy involved, yes, but what does it mean? I have two major objections to this form of analysis, where nuclear weapons are used as some kind of barometer for general energy release. The first is about the character of energy release is important — because it affects how these things are felt at the human scale. The second is about whether these sorts of comparisons are actually clarifying to the general public.
On the character of nuclear and non-nuclear blasts
The key thing about nuclear weapons is that they discharge most of their energy as heat and blast. Most of the energy release occurs over a very small amount of space and time. You can essentially regard the physics of a nuke as being a the creation of a tiny point in space that suddenly is heated to tens of millions of degrees, and this results in all of the effects that we are pretty well familiar with. The results are extremely localized: even the massive Tsar Bomba had a fireball only five miles in diameter, which is huge by human standards but minute by geological or geographical standards. The vast majority of the energy is discharged within a few milliseconds, as well. It’s a bang that matters on a human level because a huge amount of energy is released very quickly in an area of space that corresponds fairly well to the sizes of human habitation centers. The fact that a huge amount of that explosive energy (around 50%) is translated specifically as a blast wave — the thing which destroys most of the houses and people and all that — is perhaps the most salient thing about nuclear explosions from a human standpoint.
This is what a 500 kiloton nuclear blast looks like. This is not quite the same thing as what you saw on those dashboard cameras, is it?
One can see the point in distinguishing about the amount of energy over time and space by considering the Sun. The amount of energy from the Sun that reaches the Earth’s surface every moment is tremendous — equivalent to billions of tons of TNT — but it is spread out over a huge area, so instead of totally obliterating us when we go outside, it pleasantly warms us and maybe, at its worst, gives us a painful, peeling burn after several hours of intense exposure. So that is a lot of energy released over a short unit of time, but it is diffused over a very large area. The converse situation can also be considered: a given city absorbs an immense about of energy from the Sun over the course of a year, but because it is spread out in time, it isn’t anything like a nuclear explosive’s yield.
What about meteors? Yes, there’s a lot of kinetic energy in those rocks falling from the sky. But they don’t translate most of that energy into shock and heat. Even the famed 1908 Tunguska event reached temperatures “only” in the tens of thousands of degrees, as opposed to the tens of millions. You can regard the kinetic energy of such a thing as 20 megatons of yield, but the actual blast effects were more than five times less than that because the energy didn’t transfer very efficiently. (Still quite a blast, though!) The Chelyabinsk meteor was much smaller than that and it exploded in the atmosphere — a reaction more like a chemical explosive than a nuclear one. So in some sense, comparing a meteor explosion to a nuke is better than comparing an earthquake or a tsunami to a nuke, but it’s still not very exact.1
On the public understanding of nuclear explosions
My other issue, though, is about public understanding. The Chelyabinsk meteor exploded with an energy release of 500 kilotons. Is being told that going to mean anything to the average person, except to say, if it had hit the city, it would have been equivalent to a nuclear explosion? Does saying it is 20-30 times more powerful than Hiroshima mean anything to the average person, except the conjure up potentially incorrect misconceptions of what those effects would be for their cities? The truth is, as we’ve seen again and again, the average person has almost no intuitive point of reference for making sense of nuclear explosions. Heck, I barely have any point of reference and I’m constantly searching for them! The average person cannot distinguish between the results of a megaton-range explosion and a kiloton-range one unless you translate it into terms that are meaningful to them. That was the whole point of the NUKEMAP: to take these numbers and try to come up with geographical representations that make intuitive sense.
And so here’s the problem: since the physics aren’t the same, any intuitive generalization made from a nuclear analogy will be necessarily highly flawed. The effects of the Chelyabinsk meteor were not really equivalent to the 1952 Ivy King nuclear detonation, which was a nuclear explosion of 500 kilotons in yield. Even the Tunguska event was not really equivalent to a five megaton nuclear explosion in its phenomenological effects, even though it was a pretty big boom.
Still from a Sandia supercomputer simulation from 2007 of the 1908 Tunguska event, showing the blast wave formation as the meteor detonates above the ground. Intense! But not a nuke. Source.
“Hey,” you object, “we’re just trying to communicate to people it was a big explosion!” Yeah, I know, but it’s misleading. If you want to communicate the size of things, don’t talk about the energy release in terms of nukes — the effects aren’t the same. If you want to convey the effects… talk about the effects. A better way to talk about the Chelyabinsk event is to not talk about the energy output but instead to talk about the radius and nature of effects — exactly how many square miles of the city had their windows blown out? Even just saying that thousands were injured by broken glass does a lot more work to convey what this was — and how scary it was — than anything else. If you want to say, “if it had directly hit the city before blowing up” — a big counter-factual but whatever — “so-many square miles would have been destroyed,” that too would make a lot more sense.
Using nukes as a genericized way to talk about energy output is highly misleading both from the point of view of the expert, but even more so from the point of view of the layman. I really don’t see the advantage to it either way. I fear in talking about asteroids as nuke equivalents people may be trying to emphasize their threat — which is totally legitimate — but at the same time may end up inadvertently down-playing nukes. After all, if a 500 kiloton airburst only knocked in a few windows, what’s all the fuss? Yes, we can explain why they are different — but we wouldn’t have to do that if we just described the effects better in the first place, rather than taking a lazy recourse in how-many-joules-equals-how-many-megatons equations. Rather than using nuclear terminology, and then down-scaling to explain how the effects are actually not quite the same… just tell us the actual effects and forget the nukes! If one must do things in response to nukes, do it the other way around: find out the actual effects of the meteor (or whatever), then tell us what yield nuke gives you those effects. It’s less sensational, sure, but it’ll help people understand both meteors and nukes better.
- For helping me think through the physical comparisons, and providing some interesting references, I was aided by e-mail conversations with my AIP colleagues Charles Day, Paul Guinnessy, and Ben Stein, as well as my old Harvard colleague Alex Boxer. Any interpretive errors are of course my own! [↩]
It’s a very good point. On the other hand, there weren’t many 500-kt nuclear tests at the altitude of 10-20 km, so we may not have a good reference point. The Soviet Union didn’t test anything at these altitudes. Did the U.S.? Then, one can probably talk about “yield equivalent” – the yield that would produce the same effect on the ground. After all, we use TNT equivalent.
A couple of corrections – the meteorite trajectory was to the south of Chelyabinsk, not to the north. And Sverdlovsk/Yekaterinburg is not in Chelyabinsk oblast – it has its own Sverdlovsk oblast.
Well, both sides tested a lot of large bombs at high altitudes, as you know, but I still don’t think it’s a super useful way of talking about it in human terms. If the meteor had been a 500 kt nuke, the EMP effects at that altitude would have been tremendous; yet another discontinuity.
Re: oblasts — thanks. I don’t know why I thought they were in the same one — I must have been looking at the map and just noticed the cities are very close to each other and ignored the border line!
But even if the blast effects were comparable (I’m not sure they are) it still is completely misleading from the standpoint of general public understanding, since almost nobody understands the differences between high-altitude and low-altitude nuclear detonations anyway.
One more thing – Russian scientists say the energy release was about 100-200 kt: http://atominfo.ru/newsd/k0520.htm
Yet another place for Russians and Americans to disagree! 😉
There will be no EMP effects because those are due to prompt gammas (causing Compton on e-‘s at high latitude which then spiral in Earth’s B-field making EMP) which don’t exist here.
Pavel is right — the primary reason blast effects of (take your pick) 100-500 kt nuke-equivalent meteor explosion are less is due exactly to altitude. If you triggered a 100-500 kt nuke at 25km it will also not have much blast effect. ie. similar to seen in meteriod. And, no EMP for obvious reasons.
I don’t know that the folks at UWO looking at CTBTO data didn’t already take into account asymmetrical blast, although that is a good point it affects factor ~4 or so. The CTBTO people
are being kind of secretive with data which does not help here.
So, bottom line comparison with nukes is perfectly valid. (Minus the fallout and EMP!)
See eg:
http://meteor.uwo.ca/research/infrasound/infra_pub/seismic-observations%20of%20meteors-Edwards-2009.pdf
Hi Yousaf — I still don’t think it’s a useful comparison, both because the estimates are unclear on the character of the energy release (which matters, even though meteor explosions are at least a better comparison than earthquakes, tsunamis, and the like), and for the secondary reason regarding public understanding (which is totally confused on nuclear yield issues as you probably know).
I agree if you mean that the public could be better educated to know that the meteor did not explode due to a nuclear explosion. But the yield is just energy liberated — in both nuclear a meteor fragmentation this is very quick (so quick as to not make any diff. to person on ground).
kt is just a measure of energy — I don’t have a problem with anyone expressing the meteor explosion energy in those units. Should the general public know better than to think it is nuclear in origin? sure.
But if the argument is that meteor explosions are not as serious as the scary nuclear ones, that is not true. We got lucky with the altitude and the size, otherwise the city may have been largely destroyed. So they are both serious explosions.
I’m not saying it wouldn’t have been a serious explosion if it had hit the city, of course. What I’m saying is that meteor explosions and nuclear explosions are characterized very differently. The results would not be identical in a lot of ways; that they are both “serious” would be true if the blast was 15 kilotons or if it was 100 kilotons; it doesn’t really give any sense of magnitude of correctness or error.
Here’s what I’m saying, in brief: what is meant to be conveyed when we talk in terms of kilotons and “X times Hiroshima” in public articles on subjects like this? We’re trying to communicate, at best, energy output. Let’s ignore the characterization issue for meteors and pretend that it’s all just blast. Even if that’s all we’re trying to get across, does the general public have any idea what “X times Hiroshima” actually means in terms of effects on a city? I don’t think they have any clue what “exactly the same as Hiroshima” actually means, in terms of blast radiuses, casualties, and so on. It just becomes “X times infinity” as far as they are concerned. The general public — even the well educated general public — in my experience, has no conception of the difference between 1 kiloton, 10 kilotons, 100 kilotons, 1 megaton, or 10 megatons. They also have no conception of the size of the city of Hiroshima, which has become the de facto standard for “destroyed city.”
If what we’re trying to get across is the danger of what would have happened when it hit the city, there are better and more clear ways to do that — namely, by talking in terms of the effects that the nuclear reference is meant to be in reference to. It’s like me saying, “the equivalent yield of the Hallifax explosion” if you have no idea what the yield of that is — it’s not useful.
If we are only talking in terms of actually scientifically educated people, we might as well give the results in Joules or something else. I don’t see translating everything into kilotons, and then talking about which nuclear weapons had a similar output, clarifies the situation for anyone.
Ok, I guess I still don’t get it: If a meteor liberated 100 kt at 1km altitude (for sake of argument), and a nuclear device liberated 100kt at 1 km altitude, people in city below would be more or less just as unhappy. Yes, in the nuke case they would be slightly more unhappy due to radiation and fallout. But as for blast effects (and ~so for heat also) it would not be nice in either case.
Anyhow, happy to let it go at that — I am not sure what would be a good way to explain the damage from a nuke blast and meteor blast at the same altitude.
How would you explain the meteor’s tremendous prompt energy release? (honest question) I may well not be getting a subtle point.
A meteor is like a very large chemical explosion in the atmosphere. Well, not just like — it is a very large chemical explosion, more or less. That’s the prompt energy release. It’s still nowhere as hot as a nuclear explosion — orders of magnitude less.
I suspect that this does have serious implications for the blast wave characterization, but I’m not a physicist. The Sandia bit on Tusguska though is pretty interesting in this respect, where characterizing the blast effects led them to downgrade significantly the “megatonnage” equivalent. They downgraded it from 20 to 5, so that’s still bad from the standpoint of someone directly underneath it, but it’s a significant downgrade, you have to agree! That’s about a 50% reduction in the range of experienced effects on the ground, just going by rough nuclear scaling laws.
My point is that I think using “kiloton” when one means 4.184×1012 J is misleading to the general public about both these events and about nukes. It creates apples to oranges situations, when there usually either better apples to apples situations (compare earthquakes to earthquakes), or ways around such comparions altogether (by talking about experienced effects as opposed to raw energy outputs).
Yes, but as for blast effect, the Sandia piece actually says that downward blast is greater so that overall — spherical equivalent — yield may be less. It’s kind of the opposite of what you are saying: i.e. a 30kt meteor explosion may have blast effects on the ground of an equivalent same height 120 kt spherical explosion. Yes, the prompt heat is less but it is plenty hot enough to extinguish life if at low altitude. So actually the same kiloton explosion at the same altitude will, according to Sandia info, have ~4x worse effects on ground.
I still don’t see how it is misleading — also, please let me know a better way to express the yield from a meteor exploding?
The only reason this meteor blast was not just as bad as nuke was because it was higher up than typical nuclear explosions — that, and no associated radiation/fallout, of course.
PS: TNT is a chemical explosion. Similarly kt and Mt are also.
If the point is just to say, “it’s like a nuke!” then the attempt to make claims that it is equivalent to “X times Hiroshima” is unnecessary and misleading.
If the point is convey actual effects, just talk about the effects. That’s my main point. We can characterize the effects of such a thing much better if we talk about them directly, and we don’t have to worry about the messiness (which can go both ways) when comparing with nukes. Talk about it in terms of what would actually happen to the people, the city, and so on. When one uses nuke terms as shorthand for those, you actually create two problems (the effects don’t perfectly map and people don’t understand nukes) when trying to solve one problem.
OK. Yes, I agree w/ you there — it is not exactly like X times Hiroshima mainly because of the different altitude.
If it was the same altitude as Hiroshima it would be X times Hiroshima. (minus fallout, radioactivity)
We got lucky with the altitude. That’s all.
make that altitude not latitude above…
And NASA is not making these estimates btw — these guys are:
http://meteor.uwo.ca/
I’ve noticed here and there that Tsar Bomba is becoming a de facto unit of doomsy destruction. Maybe he gets his own blog post?
Eventually, yes! It’s become the Internet Standard for Big Booms.
btw, the altitude is not very well constrained by CTBTO data — the UWO folks are now using videos to try to get a better handle on altitude. The 20-30km height is based purely on past experience and not derived from current data. Numbers may all change……
at its worst, gives us a painful, peeling burn after several hours of intense exposure.
…a comment that reveals its author’s northern hemisphere location! If you’re lightly pigmented and silly enough to expose unprotected skin for more than about 30 minutes in the southern hemisphere summer you’re sure to get a decent burn.
Just a small wonky clarification on our conversation from yesterday: the explosion of the meteor is not due to chemical energy but rather mechanical shock. It basically explodes when the air ram pressure exceeds the structural strength of the meteor. The rarefied atmosphere acts like a hammer blow.
btw, I have a post here on this:
http://wmdjunction.com/130220_meteor_look_up_in_the_sky.htm
I think you need to rethink this:
What other form of energy can that get translated into? Shock, heating of atmosphere, radiation, and neutrons (for nuclear explosions) are the only means for dissipating the energy of a nuclear weapon or a meteor strike. My take is that if a nuclear bomb of the actual final energy release of Tunguska had detonated crudely at what would have been oh, the center of radiation of the Tunguska blast, the effects would have been similar. There would be a lot more hard radiation at first due to the higher heat of the nuclear bomb, but it’s not that significant.
What is different is that an asteroid strike loses energy before the final phase. It loses energy tens of miles up when it starts hitting atmosphere. So the reported energy of an asteroid strike includes
energy released well away from the final area. It’s like adding in all the energy that went into manufacture of the various materials used in a nuclear bomb (which actually would be quite substantial, I understand the energy cost of uranium refinement is generally a significant fraction of the energy content of the uranium, for example) and ignoring that they were dissipated by normal industrial processes rather than in the bomb’s detonation.
And of course, the actual energy content of an event which has as its most notable characteristic, an enormous release of energy, would be its most important characteristic. No reason not to measure energy release then in the units of which large energy releases are measured, here, tons of TNT.
So IMHO energy yield in tons of TNT is a valid and reasonable comparison to make, be it for nuclear bombs, asteroid strikes, large piles of TNT, or other large releases of energy.
Yes, nuclear explosions and those meteors that do explode (bolides) are very similar — if the Russian one exploded closer to the ground, the result would have been very similar to a nuclear explosion of the same tonnage of TNT.
Think of it this way: had Chelyabinsk been destroyed by the explosion, would such a blog post been written pooh-pooh-ing meteor explosions? I doubt it.
Sad that The Atlantic has picked up this.
Yousaf, I think you are missing out on the entire point of my post, or the article. It has nothing to do with pooh-poohing meteors. I think I’ve made that pretty clear. Please read it again if it isn’t clear to you.
Karl: This is part of why I think, in general, these energy reportings are confusing. They aren’t clear about how much of that energy would actually be translated into blast. That’s my point. And once we start talking about how much is translated into blast, we might as well just skip the nuke comparisons and start talking about the effects.
What is the difference in the blast from a 470kt nuclear weapon and 10,000 T rock moving at 18,000 m/sec rapidly retarded?
If Chelyabinsk been destroyed by the explosion would you write a blog post saying that meteor explosions and nuclear weapons are not comparable?
I didn’t say they “weren’t comparable,” I said that trying to compare them leads you to apples to oranges situations where people fudge the numbers, fudge the effects, make foolish “X times Hiroshima” proclamations, and leave people more confused that enlightened.
Again, read the post more carefully if you think I’m saying that meteors should be pooh-poohed. I’m not. I’m saying that explaining their effects in terms of nuclear weapons 1. misrepresents a lot of the differences in how that energy is deposited, 2. doesn’t really mean a lot to most people anyway since they don’t know the difference between 10 kilotons or 100 kilotons 1000 kilotons.
On point #1, reasonable people can disagree whether the differences in the nuclear release of energy or the meteor release of energy are similar enough to be more or less equatable or whether different blast radii, different heat properties, different mechanisms of energy release, or the fact that meteors lack a whole host of effects characteristics of nuclear explosions, and so on. Any analogy requires throwing out some dissimilarities, I’m happy to concede that.
On #2, though, I think there can be no real disagreement. Even trying to explain what a 10 kiloton blast means in human terms is hard and requires appeals to things other than the kilotonnage — it requires appeals to effects. My entire point, if you wanted to boil it down, is rather than assume nukes can be understood by the general public as a proxy way of explaining effects, just explain the effects.
I still completely disagree with you.
People understand the damage that a Hiroshima type device can do, and an equivalent kilton of TNT rapid released as the aerodynamic pressure retards a meteor, will have extremely similar effects and Hiroshima is a *excellent* way to describe what would happen to a city below a meteor explosion if the nuke blast and the meteor blast occur at the same altitude.
People saw what Hiroshima looked like — this is a good way to explain what the effects of an equiv. kt in meteor would do.
You say: “reasonable people can disagree whether the differences in the nuclear release of energy or the meteor release of energy are similar enough to be more or less equatable or whether different blast radii, different heat properties, different mechanisms of energy release, or the fact that meteors lack a whole host of effects characteristics of nuclear explosions, and so on. Any analogy requires throwing out some dissimilarities, I’m happy to concede that.”
Maybe reasonable people but not any scientists. If they both have the same kt of TNT exploded, the bulk effects are the same — aside from radiation and fallout, the blast effects are v. similar.
cf. Tunguska
If you want to learn more about the subject read eg.:
http://www.nature.com/nature/journal/v361/n6407/abs/361040a0.html
Or ReVelle, D. O. J. geophys. Res. 81, 1217−1230 (1976).
It is not wise to start pontificating on this, thinking you know what is best for the common people without getting things straight yourself first.
After you’ve read the ref’s we can talk further.
Let me know if you have reason to believe that there is a difference in the blast from a 470kt nuclear weapon vs. a 10,000 T rock moving at 18,000 m/sec rapidly retarded, if they explode at the same altitude?
I agree with the initial post. As for the debate here between Yousaf and the initial poster, I believe the issue would be resolved immediately if either one of you used the equations in the book ”The effects of Nuclear Weapons”, and working backwards from the observed effects of the Chelyabinsk explosion. Sure there is also the issue of nuclear weapon blasts being spherical and meteor explosions are probably more directional.
The point being, that a rough yard stick can be determined in this manner. (HANE) high altitude nuclear explosion data is available. Personally, my back of the envelop calculations put the explosion at equivalent to the blast from a 50 kiloton nuclear explosion at the same ~ 20 km height.
The Cubed root law is your friend.
Thank you I am intimately familiar with ”The effects of Nuclear Weapons” which I studied fairly thoroughly whilst getting a PhD in nuclear physics.
Yes, you are right of course — but that is the point: the only reason the blast effects were less from the meteor is that it was higher up. I have no disagreement with that view — obviously.
I made this point above:
========================
K. Yes, I agree w/ you there — it is not exactly like X times Hiroshima mainly because of the different altitude.
If it was the same altitude as Hiroshima it would be X times Hiroshima. (minus fallout, radioactivity)
We got lucky with the altitude. That’s all.
========================
Also see the post from JB below.
It beggars logic to say that it is OK to express nuclear weapons yield in terms of chemical TNT, but not meteors for some reason. I made this point above several days ago:
“TNT is a chemical explosion. Similarly kt and Mt are also.”
If two explosions are of equivalent chemical TNT yield (at the SAME altitude, of course) their blast effects will be very similar: similar enough so as to make no difference to people dying on the ground.
Yes with a pressure transducer very close to the center of the explosion and an oscilloscope you could maybe tell one apart from the other (before you die) — but then with a pressure transducer and an oscilloscope very close to the center of nuclear blast vs. an equivalent TNT blast you could also perhaps tell the difference.
The fact that people routinely use chemical TNT to explain nuclear blast effects is in itself an obvious reason this blog post is internally inconsistent.
Seems to me that the comparison between a meteor and TNT is more similar to each other, than the an atomic/nuclear bomb.
Perhaps if we compare it to the non-radiation portion of the atomic bombs.
It was due to the extreme altitude that mitigated the damage on the ground due to the blast effect.
That is exactly right.
It beggars logic to say that it is OK to express nuclear weapons yield in terms of chemical TNT, but not meteors for some reason. I made this point above several days ago:
“TNT is a chemical explosion. Similarly kt and Mt are also.”
Good news– or maybe not-so-good, from Alex’s point of view, since an estimate of meteor impact energy in “kilotons” comes with it– may be found at NASA’s Near-Earth Object Program site.
I just asked Donald Yeomans of JPL about the, um, “U.S. Government sensors” that, for a while, released occasional information about meteoric fireballs that were picked up from time to time.
As I understand it, there are satellites staring at the Earth, looking for a sudden flare of light with the characteristics of a large rocket launch. Naturally, the details of their operation, and the data they gather, are sensitive defense information. However, they are good at picking up meteoric impacts, and in the 1990s persuasive DoD insiders succeeded in arranging the release of fireball reports, recognizing that they would be very useful in characterizing the number, spatial distribution, and energy release of incoming near-Earth objects.
It’s classic example of data gathered for military purposes that, when declassified, can be useful to scientists in the wider world.
The program of releasing declassified reports seems to have stopped after 2008. Scientists were not happy.
Imagine my surprise when Dr. Yeomans told me that releases of fireball data have begun again. Today. On his Web site.
The only item on the list is the Chelyabinsk event, at the moment. Nevertheless it is good to see data flowing again.
Looks like it came awfully close to the Yamantau Mountain Complex as well…