Meteor propter hoc

By Phil Plait | December 14, 2008 6:09 pm

[Note: If you want to Digg this article, please go to here and not to the link in the button above. While I'm glad someone else submitted this to Digg, there was no specific information posted on that link. And if none of this makes sense to you, don't sweat it. Just enjoy the article below. :) ]

In Auckland, New Zealand recently a warehouse was set ablaze. It was quite the inferno, needing a huge effort to quell it.

No one knows what started it… but rumors are spreading that it was a meteorite that did the damage. Several people saw a fireball in the sky, and it happened around 10:00, around the time the fire started.

Case closed, right?

Photoshop of a meteor over Auckland fire

Bzzzzt. Nope. I will almost guarantee a meteorite did not start this fire! Why not?

Meteors are chunks of rock or debris that enter the Earth’s atmosphere. They violently compress the air, heating it up — it’s not friction that does the heating, contrary to common belief. But common wisdom also says that meteorites would hit the ground still burning hot, and cause fires wherever they land. And after all, we’ve seen it in countless movies!

However, there’s a piece of info you should remember here: that’s in the movies. In real life, meteorites don’t work that way. A small meteoroid (the solid part of the glowing meteor) will burn up rapidly, leaving nothing to hit the ground. If it’s somewhat bigger, like the size of a car, it’ll explode high in the atmosphere, and then pieces of it will rain down. However, those smaller pieces fall relatively slowly, and have plenty of time to cool down before they hit. The recent fireball over Canada shows that, as did a rain of meteorites that hit Chicago a few years ago did too. No fires were caused by those rains of rocks from space, because they were cold when they hit.

A piece of rock or metal large enough to retain its heat when it impacts the ground would be pretty big, like over 100 meters across. Those tend to be a bit more obvious when they impact, since they explode with a yield equal to that of a 15 megaton blast.

That might do a bit more damage than start a warehouse fire. Had something like that been the cause of the Auckland warehouse fire, there wouldn’t be anyone left in the city to report it. There would be a smoking hole a mile across.

I’ve heard reports like this one many times. They always — always — turn out to be non-extraterrestrial in origin. Just because a bright meteor was seen does not mean it caused the fire! That’s a logical fallacy: post hoc ergo propter hoc, "after this therefore because of this." There’s a reason that’s called a fallacy.

So that’s why I think a meteorite didn’t cause this fire, and I’m pretty sure there’s a more down-to-Earth explanation here… at least one that started off down-to-Earth and didn’t just end up that way.

Tip o’ the Whipple Shield to BABloggee Bret Hall.

Comments (80)

  1. doofus

    I’m sorry, I’m not quite following.
    What causes the meteoroid to go away?

    Is this it:
    a. the solid meteoroid is moving through the air
    b. the air is thus being compressed in front of it
    c. the compressed air gets hot
    d. the hot air slowly melts the material of the meteoroid

    So it’s not the air “rubbing” the meteoroid into nothingness. Like friction between sandpaper and wood, eventually gets rid of the wood (well, ok it makes sawdust, the wood doesn’t vaporize, but you get the analogy)

  2. Carl Smith

    Quite right. I’m pleased to say I saw this meteor – it was awesome, BTW – and there’s no way it had anything to do with the fire. I had to laugh when I first read reports tying the two events together.

    Oh well, it’s fun to see a bit of attention down our end of the world anyway.

  3. Katydid

    “Non-extraterrestrial”? You mean terrestrial? ;)

  4. As for the meteor…

    He didn’t start the fire….

  5. So, then we can assume it wasn’t the Northern Lights that set fire to Sarah Palin’s church and caused a million dollars damage???

    ***I do not condone any atmospheric phenomenon setting fires.***

  6. Nick s

    Given that Auckland is basically a strip of ash linking together a few cinder-cones and separating the craters of the former-cinder-cone volcanoes also known as Auckland harbour, and Manakau harbour, if a 15KTon equivalent crater did appear, I’m not sure anyone would notice/care….

  7. r chalmers

    Perhaps the stony or irony meteorite fragment hit an electrical panel in the warehouse. Cause and effect-ish but not implausible.

  8. I drove past that building last night! Hadn’t heard the meteorite rumors till now haha but I was wondering about what had happened there…

  9. Cindy

    My husband just told me that the article appeared on Slashdot. I told him that I remember Phil blogging about this before and that any meteorites that do hit the ground end up being pretty cold, but I couldn’t remember the details why. Thanks for the reminder, Phil.

  10. Navneeth

    A good old piece of Bad Astronomy. Nice.

    Oh, and don’t you think it’s a little strange for the firemen to be fighting the fire even before the meteor(ite) hit? :D

  11. JoeSmithCA

    @Kevin F.
    The meteor totally set the fire, witnesses saw it getting into a car and driving away from the scene of the crime.

  12. MarkT

    Was hoping you’d pick this one up. I saw the flash of the meteor as I was driving home on Saturday night and was somewhat embarassed to hear people linking it to the fire…!

  13. Gurnipikus

    What if the meteor punctured a gas tank that was inside of the building violently releasing all off the gas it contained and then bounced around on some metallic object creating enough sparks to ignite the gas just previously released? The meteor doesn’t have to be hot to start the fire…

  14. Sauss

    The pall of smoke looked pretty awesome from my place in Grey Lynn, back-lit by the extra-large full moon. So I think the moon caused it. True story.

  15. Neurosaur

    @JoeSmithCA I didn’t catch that, but the police chase was pretty wild.

  16. kebsis

    Wouldn’t it be possible for a meteor to smash a gas line or something though? I mean obviously it’s unlikely that a meteor started this fire, but I imagine it would be possible if the rock were large enough to pierce the house.

  17. Dave Hall

    But . . . .You have a picture of it and the fire!

    Next thing you’ll be telling me is pictures in the internet can be faked.

  18. While a good idea to keep pretty sceptical about the whole event, I’ve been following the story since the 13th and have since compiled a few eye witness accounts of the meteor(ite). Whilst I still think “Exhibit A” will be a petrol canister rather than a meteorite fragment, just because post hoc ergo propter hoc is a prudent primary course of action, there is a slim chance that the meteorite might have initiated the fire (through primary or secondary means). Just because we “don’t know” what happened doesn’t mean the two events weren’t related, you can use the same arguments for and against: jumping to conclusions is not the correct course of action.

    I am no pro when it comes to meteorite physics, but I have seen footage and resulting studies on meteorite debris… it looked pretty hot to me (the flame and smoke kinda gave that away).

    Would be nice to see some actual footage of the meteor(ite) though, perhaps we’d get a better picture about where the possible meteorite debris landed (whether or not it was anywhere near the warehouse)

    Cheers :-)

    Ian

  19. mullingitover

    This meteor is just another example of the many deadly attacks on our planet from space. We must deal with this aggression and ATTACK SPACE. We need to seriously get up there and wage war on some solar systems and galaxies, and even teach those constellations a lesson or two. Only then will space be free, and freedom-loving people will be safe from the tyranny of random meteor showers. Better to fight it there then to fight it here at home.

  20. Mike

    Actually, it was a rather large meteorite, about 100 m in diameter or so and the town would have perished was it not for the Doctor!

    “Well, you know, nothings perfect.”

  21. TheWalruss

    Ian:
    I’ve always thought it worked like this: Meteorite enters Earth’s atmosphere, its outside heats up due to air compression. When it hits the ground, its outside is still hot due to all the kinetic energy imparted to the surroundings. But then it’s sitting in its little crater, and the inside is still as cold as space, quickly cooling the outside. So a fresh meteorite might be sitting in a burning crater but covered by frost.
    Of course, not quite so dramatic usually. Smaller meteorites lose their kinetic energy high in the atmosphere and float down at their relatively lazy terminal velocity. Then there’s no cool-looking burning crater.

    I didn’t know what the size limits were. It’s unfortunate that the smallest meteorite that can cause burning crater is already big enough to blow up a city. *sadface*

    What if an unusually dense and well-structured chunk of metal of the right size crashes into the planet, such that it doesn’t explode in the air and only releases as much energy as a stick of dynamite or so? Is that possible?

  22. Peter B

    Perhaps the local constabulary should track down whoever it was that started the rumour about the meteorite causing the fire. Mayhap that person had a reason for trying to make a connection between the fire and the meteorite…

  23. AJ

    Well on December 8th there was a massive fire at another warehouse in Auckland. This one was a Mitre 10 (similar to Home Depot).
    My parents are (well were, havent seen each other in years) friends with the guy who owns the building. It was a very old building.

    These warehouses have very shoddy if non existant fire alarms, one witness who was in the store said he smelled smoke, turned around and saw a wall at the other end of the building going up in flames.
    One staff member is quoted as “There was no fire alarm, no one knew where fire alarms were and when we had a look around there were no fire alarms available. No fire extinguishers, nothing like that. There was no game plan and they never did fire drills.”

    If they couldnt be bothered installing fire alarms what makes you think that their wiring would be 100%? I’d put my money on an electrical fire.

    Oh by the way, any kiwis know of any NZ stores that stock phils book? And other skeptical books, Sagan, Randi etc. I was thinking borders but havent been in to check yet.

  24. Mang

    I seriously doubt that a meteorite would have enough momentum or heat to cause a fire.

    Look at the photos of the Alberta meteor fragments from last month. They were found on the surface of a frozen pond! If they had large momentum or heat then they would not have been found as they would have punched or melted their way through the ice.

    Not 100% case closed, but I would want to see some pretty convincing evidence. I’d start with (1) Fire Marshall can’t find a cause and (2) confirmed meteor found in remains of wharehouse before answering the question of how.

  25. TheWalruss

    We should consult a couple of psychics and astrologers about the matter – the astrologers can tell us if it was a meteorite, and the psychics can tell if the astrologers are lying…

  26. AnthonyK

    Yeah, astrologers need some imput into this. They should run properly scientific birth charts for the building, the area, and the owners of the warehouse. If, say, the meteorite appeared in a “fire” sign (25% probability, right?) while the warehouse was also currently a fire sign (which I suppose relegates the probability to 1/8), and then factors in the fortune charts for the owners and the insurance company, together perhaps with a properly conducted meta-ananysis, properly weighted, for the employees, we should be able to come up with a genuine figure for the probability that the meteroid did actually cause the fire.
    Now, I’m not saying that this would be 100% accurate, but it would at least give us a chance to use astrology, with its 1000s of years of unchallenged history, in a useful, scientific way. Or are you too narrow-minded to accept this evidence?

  27. TheWalruss

    @AnthonyK:

    I can’t tell if you’re kidding :(

  28. AnthonyK

    Ah, the horrors of the interweb. Yes I am – please note the combination of “scientific” and astrology. :)

  29. Nick

    “They violently compress the air, heating it up — it’s not friction that does the heating, contrary to common belief”

    If not friction, then what causes compressed air to heat up?

  30. TheWalruss

    @Nick: Boyle’s Law FTW!

    @ AnthonyK: *phew*! I was afraid you were a nutter – very convincing, indeed! Just because you and I chuckle at using the term “scientific birth charts” doesn’t mean everyone does, unfortunately!

  31. Nick Rudzicz

    @Nick:

    The compressed air causes the air to heat up. That is, compression of any substance will increase its heat: I believe the canonical (and easiest to implement) example is when you repeatedly bend a paperclip back and forth…you’ll note that it heats up where you bend (i.e., compress) it. In the case here, the meteor compresses the air just in front of it (the bow wave/shock?), which heats up that air.

    Also, this:

    “Had something like that been the cause of the Auckland warehouse fire, there wouldn’t be anyone left in the city to report it. There would be a smoking hole a mile across.”

    Quote of the morning.

  32. Why does Phil keep kill these peoples fun with the truth. ;-) Their movie view of the world is probably the only excitement they get.

  33. Nick

    @ Nick Rudzicz
    Yes, but what causes something being compressed to heat up?
    Friction!

    So the meteor heats up due to friction.

  34. flynjack

    The bugs are at it again, sending rocks at us from Klendathu! Buenos Aires be afraid, be very afraid!

  35. Knurl

    @Nick When a volume of gas is compressed, the heat content remains the same but it becomes concentrated into a smaller volume and temperature increases. That’s how a diesel engine operates without spark plugs – the air/fuel mixture is compressed to the point there the air/fuel temperature reaches the ignition point. Compression ratios in a gas engine are typically 9.0 – 9.5 to 1 but in a diesel it is typically 22.5 – 25.0 to one.

  36. Todd W.

    @TheWalruss and AnthonyK

    Not only would the psychics be able to tell if the astrologers are lying, they would be able to locate the missing metorites, with razor-sharp accuracy, somewhere near a body of water. Oh, and I’m getting the letters “M” and “F”.

  37. Mang

    @the Walrus.

    Thanks I can never remember all those laws are about: Boyle, Dalton, Charles, Martini’s. Other than Martini’s I remembered PV=nrT and always got the answer (unless it was name the law …). And just to head off any objection, AFAIK, Martini’s law is only taught to Scuba divers.

    Haven’t astrologers been using the wrong star positions for some time. Not having accounted for precession.

    BTW, while the Alberta fragments were not hot, they were warm when they came down because they managed to melt themselves a few mm into the ice.

  38. Nick

    @ Knurl
    Yes, I know compression causes heat. But why?
    Answer: Friction.

  39. The Raptor

    Pressure X Volume = Temperature. No friction needed. Increase the pressure, while volume of air that is in front of the rock remains the same (more or less), and the temperature will go up. Tada, heated air.

  40. TheWalruss

    Isn’t that the theory behind scramjets? Just to go really really really fast, shoot some fuel into a funnel, air enters funnel really really really fast, gets really really really compressed at the back of the funnel, ignites itself, blasts burniness into exhaust nozzle, produces thrust.

    Supposed to reach Mach 15 or 25 or something crazy. I read about it someplace, but I don’t know if it was a cool “what-if” scenario or if somebody is trying to build it. Sounds like a good start to a space plane…

  41. No, I’m pretty sure this was an alien Roger Ebert offering his review of the Keanu Reeves re-make of “The Day The Earth Stood Still”.

  42. TheWalruss

    @Nick: No, I don’t think it has to do with friction. In a smaller space, the same number of molecules are closer to each other, which means they bounce against each other more often and more furiously, which is temperature. That’s my understanding, anyway.

    Another thing that just struck me is that a compressed gas should have lower entropy than the same gas in a bigger volume. Since it’s a closed system and entropy decreased, enthalpy should increase, right? Or am I being loony? I guess it’s not really a closed system because an outside force did the compressing, which is what adds the energy that is stored as heat. Ahhh, I think it’s starting to make sense to me now…

  43. Maura

    It’s amazing how much things don’t change. Ancient people would see stuff like meteors or eclipses in the sky and assume those things caused (or at least portended) their earthly problems like crop failures or deaths. They had the excuse of a limited understanding of the cosmos. But I’m pretty sure they have science in NZ – no excuse there.

    Also, I heart you for “post hoc ergo propter hoc”. It’s astonishing how often that phrase is appropriate in conversation and how seldom it is understood.

  44. Nick

    Okay, one more time and then I quit out of frustration…
    If not because of friction, can someone tell me scientifically why compressing air causes heat?

    It seems like all I get as an answer is “Just because it does”.
    Maybe it’s a Christmas miracle!

  45. TheWalruss

    ^— This guy never took physics (or other real science) because he “tested out” of all that in high school, thinking he was being super clever. What a bad idea that was. :P

  46. TheWalruss

    *never too physics at a University level

    Need to check what I write before submitting, too.
    Enough of this spam! Back to lurking, TheWalruss!

  47. TheWalruss

    Ok Nick, let me try again :)

    Imagine a balloon filled with air. System is at an equilibrium at room temperature.
    Someone squashes the balloon to a tiny fraction of its previous volume using a tremendous force (sayyyy – a meteorite hits the balloon).
    Energy is thus being added to the system.
    What happens when energy is added to a system? The system “heats up”.

    It’s just as fundamental as “friction causes heat”, which you seemed to like before. Does that make sense?

  48. Tim J

    The heating up of a compressed gas has nothing to do with friction. The temperature is a measure of the energy per unit volume of the gas. So if the gas – and hence the energy of its molecules whizzing about – is compressed into a smaller volume, the temperature is automatically higher. That IS the cause. Friction is a separate process. The cause is simply conservation of energy. There doesn’t need to be another one.

  49. antaresrichard

    Well, the only “meteors” to remain oven hot hours after they’ve impacted sideways, are Martian war machines! Look out, this may be but the red vanguard of those commie constellations!

  50. Greg in Austin

    Argh, the laws of physics be a harsh mistress!

    Compressing more air into the same volume adds heat.
    Releasing compressed air from that same volume looses heat.

    Ever put air into a scuba tank? The tank gets warm as the pressure increases.
    Ever used one of those cans of air for your desk? As you spray the air out of the can, the can gets cold.
    Same principle.

    As a meteor comes blasting in at a gagillion feet per second, the air pressure in front of it is so great, it makes the perty fireballs we see streak across the sky at night.

    8)

  51. Knurl

    @Tim J Exactly. If you have a liter of air that contains 1000 calories (1 calorie per ml) and compress that same volume down to 1 ml, you end up with 1000 calories per ml. NO HEAT ENERGY HAS BEEN ADDED – the same amount of heat energy becomes concentrated into a smaller volume and the temperature increases since there is a smaller volume.

  52. John B

    OK – Fine, compression is enough to heat the air in front of the meteorite to incandescence. I have no problem with that.

    However, what causes the compression? Why, the meteorite ramming into the atmosphere. If the meteorite were very aerodynamic (i’m thinking a needle, point-on) versus a brick (very mucch NOT aerodynamic) – would the compression be different?

    Yes. crossectional area will make a difference. This can be seen in part by the difference between a meteorite and, say, the dart (theoretically) dropped by a Thor system from Pournelle’s pre-SciFi days (http://en.wikipedia.org/wiki/Kinetic_bombardment is a good quick link for a quick overview if you don’t recognize the term)

    What else is the area of the cross section (or, more commonly, ‘contact patch’) used for? Why, determining the magnitude of the frictional force experienced.

    Hrmm? Related?

    -John

  53. Amos Kenigsberg (Discover Web Editor)
  54. Regner

    @Nick et al.
    Heat is not that well defined a concept, so in physics we prefer to use the terms energy and temperature. Several bloggers have already pointed out that when you have a volume, V0, of gas at a certain temperature, T0, and then decrease the volume to V1, then the energy density will increase by approximately V0/V1. Some energy might be added by the process of compressing the gas, but that’s a minor contribution. A great deal of work has to go into compressing the gas, but that in itself does not change the total energy of the volume of gas – only the energy-density. If the gas can undergo ionization, dissociation, chemical reactions or phase-changes during the volume change, some of the increase of energy-density will go into those reactions, instead of contribute to an increase of temperature.
    Temperature is directly related to the average kinetic energy of the particles in the gas. When the energy-density is increased, the energy per particle will increase since the particle numbers are unchanged (unless some of the above reactions are involved). Most of that energy increase will be kinetic, as opposed to potential (there are only those two kinds), where the potential energy arise from Coulomb interactions between electric charges of the gas particles (net charges in plasmas and van der Waals like forces in cooler materials). The potential energy does change under some of those reactions mentioned above, but otherwise not.
    Friction is not part of the picture. Friction increases the temperature of materials by directly imparting kinetic energy to the particles that are affected (i.e., in the boundary layer).
    Note on coolness of meteorites (they are cool!): ablation, caused by air-friction, constantly ‘scrapes’ off the hottest layers of the meteorite, so the bit that eventually hits Earth hasn’t actually been heated that much.

    Regner, astronomer at Mt. Stromlo Observatory, Australia

  55. guestwork

    Just to point out the obvious (as has been done above already, but I feel like it, so sue me): they’re icy cold because they come from space, where it is, well, cold kinda sorta (I’m of the kind who like to think space has no temperature because it’s a vacuum, but I know how inaccurate that thinking is and you know what I mean, so sue me again). The brief traverse through the atmosphere -if they survive it- is not sufficient to heat them up significantly at all, and all that little heating up happens only on their surface anyway, while they’re still deeply deeply deeply frozen at the core.

  56. Chris P

    So if there is no friction then why does it slow down? Is the miracle heating effect responsible for slowing down too?

    The answer given is half assed. Obviously part of the heating is due to friction. It just sounds better to make the radical claim when it is not strictly true.

    If there is an atmosphere – there is friction – simple fluid dynamics.

    Chris P

  57. Amos: I submitted this blog post as a followup to Slashdot.

  58. AnthonyK

    Huh, you scientists are your fanciful “theories”. Has anyone ever seen a meteoroid heat up? Has anyone ever seen “heat” at all – and I don’t mean the effects of heat, but heat itself? I think not. And friction is just god’s way of making things sticky. So there.

  59. Chris P

    OK – lets try this again. We appear to be physics challenged. The gas gets hotter because of the work of compression – not “just because”. It’s the same amount of gas so it has to have work done on it to raise its temperature. It has a specific heat.

    Chris P

  60. Rob

    “Obviously part of the heating is due to friction”

    Perhaps, but it would be a very small portion. The shockwave that forms in front of the meteor is itself in front of a layer of slower-moving air that surrounds the meteor.

    The best example I’ve heard explaining this is the heat tiles on the Space Shuttle. They are fragile and can easily be broken using bare hands. If there were enough friction to create the heat necessary to make them incandescent, they would all be immediately stripped off.

    The explanation isn’t that thorough in this article (it was a digression!), but it’s not exactly difficult to look up elsewhere.

  61. Greg in Austin

    Chris P said,

    “So if there is no friction then why does it slow down?”

    Wait, who said there is no friction? Phil said that compression causes the heat, but he didn’t say friction does not exist.

    Objects large enough to survive the heating from compression will certainly slow down, due to the increase in atmospheric density. As others have said, the object will slow down to its terminal velocity, which is certainly caused by air resitance.

    8)

  62. Knurl

    The kinetic energy of the moving meteor compresses the gas (does work). It increases the density and concentrates the available energy into a smaller volume – the number of calories (at 4.1840 joules per calorie) increases per unit volume, so the temperature increases. Air isn’t dense enough to create enough friction to increase the temperature by anything but a negligible amount. The meteor slows down rather quickly for the same reason that you car slows down when you lift off the gas – aerodynamic resistance (rolling resistance is the minor component).

  63. Chris P

    He said “It’s not friction”. Not friction =no friction. Engineering is a very precise science that requires precise English. If he was being correct he would say “It is mostly not friction”.

    I don’t have my copy of Hoerner at hand to check the numbers but there are fundamentally two types of drag associated with a body moving through a fluid. One is called pressure drag which is what is causing the compression heating and the other is friction drag caused by the passage of fluid over the skin.

    Just because you can break the tiles with your bare hands doesn’t make them weak – it may mean they are brittle. The frictional forces are low otherwise the shuttle wouldn’t fly well.

  64. The Mad LOLScientist, FCD

    I read about this yesterday via a link from Twitter, just in time for last night’s Discovery Channel show on Sodom and Gomorrah. Two talking heads proposed, in all seriousness, that the stuff that rained down on the two doomed evil cities was hot debris from a huge meteor explosion over western Europe.

    Bah. Humbug. I spent the whole hour trying to explain to my friend that by the time meteors hit the ground, they’re nowhere near hot enough to cause fires, and that the only way I could imagine that happening would be if (as mentioned above) the thing hit a gas tank hard enough to rupture it and struck a spark. He wasn’t buying it.

    I’ve heard from lots of people that the DC seems to exist primarily to confoozle people about all things scientific. More and more, I find myself agreeing with them. :-P

  65. Trebuchet

    I feel compelled to point out that the original blog post contains no book-shilling at all. None. That’s some kind of recent record, especially for a subject that had a pretty clear tie-in to the subject of the book!

    And I still have to wait until a week from Wednesday to unwrap and begin reading my copy!

  66. Dave Hall

    Trebuchet:

    A book on the threat of meteoroids–what a great idea.

    Maybe someone we know here might try writing one. Something with a catchy title like: “Doom From Above” or “Comet Catastrophies.”

    Seriously, I was amazed Phil didn’t add a sentence or two. Maybe he figures we all got the message and book sales are high enough.

  67. @Regner “Friction is not part of the picture. Friction increases the temperature of materials by directly imparting kinetic energy to the particles that are affected (i.e., in the boundary layer).
    Note on coolness of meteorites (they are cool!): ablation, caused by air-friction, constantly ’scrapes’ off the hottest layers of the meteorite, so the bit that eventually hits Earth hasn’t actually been heated that much.”

    It’s obviously an incomplete picture being presented so far. The compression and increase in temperature of the air (called adiabatic heating) in the shockwave just in front of the meteor does NOT account for the meteor itself heating up or ablating. There are several possible heat transfer mechanisms for getting the heat from the air shockwave to the meteoroid – thermal conduction, thermal convection, radiative transfer, etc. but I think friction is probably a very efficient mechanism. Thermal conduction and thermal convection are probably very minor influences at the high altitudes and low air densities where ablation is taking place. So I wouldn’t be so quick to kick friction out of the picture entirely.

  68. @BA “A piece of rock or metal large enough to retain its heat when it impacts the ground would be pretty big, like over 100 meters across. Those tend to be a bit more obvious when they impact, since they explode with a yield equal to that of a 15 megaton blast.”

    http://en.wikipedia.org/wiki/2007_Peruvian_meteorite_event

    At 11:45 local time (16:45 GMT) on September 15, 2007, a chondritic meteorite crashed near the village of Carancas in the Puno Region, Peru, near the Bolivian border and Lake Titicaca (see map box on right). The impact created a crater larger than 4.5 m (15 ft) deep, 13 m (43 ft) wide, with VISIBLY SCORCHED earth around the impact site. A local official, Marco Limache, said that “BOILING WATER started coming out of the crater, and particles of rock and cinders were found nearby”, as “fetid, noxious” gases spewed from the crater. The crater size was given as 13.80 by 13.30 meters (45.28 by 43.64 feet), with its greatest dimensions in an east-west direction. The fireball had been observed by the locals as strongly luminous with a SMOKY TAIL, AND SEEN FROM JUST 1000 METERS (3280.84 FT) ABOVE THE GROUND. The object moved in a direction toward N030E. The strong explosion at impact shattered the windows of the local health center 1 kilometer (0.62 miles) away. A SMOKE COLUMN was formed at the site that lasted several minutes, and BOILING WATER was seen in the crater.

  69. @Trebuchet “I feel compelled to point out that the original blog post contains no book-shilling at all. None. That’s some kind of recent record”

    Forget the Star of Bethlehem! What physical explanation can anyone come up with for this miracle? :)

  70. TheWalruss

    Wow, it’s fun to read what everybody thinks about the meteor-heating question.

    I think what we can gather from all this is:
    1) The meteorite heats the air due to compression.
    2) Compression makes the air hot enough to glow because of conservation of energy: the same amount of energy suddenly occupies a much smaller space, which equates to increasing “hotness”.
    3) If friction causes the meteorite to slow down sufficiently before impact, we get a cold spacerock that plumps down “gently” at terminal velocity.
    4) If friction isn’t sufficient to slow it down, we get a massive rock surrounded by burning air slamming into the planet at many times the speed of sound.

    Neat! Refresher in thinking critically about physics! Thanks guys!

    I still think we should ask the astrologers, though ;)

  71. Tom Marking, it’s not clear even now what happened in Peru. A 10 foot rock/iron ball falling at speed (200 kph, maybe) would still not be too hot when it hit, and I don’t think the energy from impact is enough to boil water. However, the presence of noxious chemicals means there was gas under the impact site, and if released may have been confused for boiling water.

    Mind you, those reports were mostly in newspapers, and they notoriously cannot be trusted for accuracy, especially right after an event like this.

  72. Oh– I meant to add, something that large in general will suffer an explosion high in the atmosphere, like what happened in the Sikhote-Alin impact. It’s possible, though still unlikely to me, that there would have been much heat left over from that. I can’t say it’s impossible though.

    Remember too, that left a nice crater in the ground. There was nothing like that with this warehouse fire. I am still pretty sure this was unrelated to the fireball. We still have no reports of the direction of the fireball, and whether it was anywhere near the actual location of the warehouse. People are in general TERRIBLE witnesses for meteorite impacts; they cannot judge distance at all in these cases.

  73. flynjack

    On the more serious side meteors have fusion crust on the exterior from the heating on entry. this crust is very thin and wears off in the atmosphere from rain and weather (thus most meteors look very much like common rocks to the untrained). Meteors do get hot, only they cool considerably in the lower atmosphere before they hit dirt. Fresh fallen meteorites have been picked up and were only warm to the touch. I agree with Phil this fire is far more likely to have been caused by human causes, I’d put my money on that!

  74. IVAN3MAN

    Phil Plait, I tried twice to submit an abstract of an article — with a link — which gave a possible explanation to the Carancas impact event that Tom Marking referred to above, but it got ‘spammed’ both times by your so-called anti-spam filter! :mad:

    Fortunately, I wrote it out on WordPad and saved it on my computer’s hard-drive. So, it’s not a problem for me to resubmit it, if you’re interested;
    otherwise, you can live in ignorance.

  75. I saw this fireball over Auckland (or at least the initial flash of light and looked up to see the glowing orange trail across the night sky). It was personally one of the most incredible things I have ever seen. But I knew immediately what it must have been.

    I was amused later to hear that people were ascribing the Ponsonby fire to this! Personally I would describe the meteor fireball as originating in the West and travelling towards the ESE. I live West of the suburb of Ponsonby in Auckland about 20 km out. It’s “apparent” trajectory was therefore “towards” the city. But it was also apparent to me that it was at a very high altitude. I have also heard of eye witnesses to this event as far south as Motueka in the South Island of New Zealand. Which I think confirms the high altitude. I’m obviously no expert but I would think these things rule out any possibility of a landfall in or around Auckland city.

  76. @IVAN3MAN “but it got ’spammed’ both times by your so-called anti-spam filter!”

    Are we back to mangling the URL’s once more? Sigh! Moan! Sigh!

  77. There is definitely something wrong with this topic. It won’t accept any large post with or without URLs.

  78. IVAN3MAN

    @ Tom Marking,

    That’s what I mean! There was nothing wrong with the URL, but my post still got spammed!

  79. Chris P

    OK – Hoerner says the drag coefficient of a meteorite is around 2. SO – Somebody needs to cite a real reference that gives the pressure drag/ friction drag breakdown.

    There are several reasons why it may not be so hot when it reaches the ground. Ablation obviously occurs and heat build may be counterbalanced by heat transfer back into the air.

    I’m not satisfied with glib.

    Chris P

  80. I am so glad that you addressed the question, that it is compression and not friction that heats a meteor. I have believed that it is compression that heats a meteor, but even the science channel has attributed friction being the cause of the heat. This has been so annoying to me and hope the science channel admits to the truth. Thank You.

NEW ON DISCOVER
OPEN
CITIZEN SCIENCE
ADVERTISEMENT

Discover's Newsletter

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

ADVERTISEMENT

See More

ADVERTISEMENT
Collapse bottom bar
+

Login to your Account

X
E-mail address:
Password:
Remember me
Forgot your password?
No problem. Click here to have it e-mailed to you.

Not Registered Yet?

Register now for FREE. Registration only takes a few minutes to complete. Register now »