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Why Meteoroids Explode Before Hitting the Earth (qz.com)

Posted by BeauHD on from the behind-the-scenes dept.

According to a new study from Purdue University, scientists have figured out why meteoroids explode before hitting the Earth. "The research, published in the December issue of the journal Meteoritics & Planetary Science, shows that as meteoroids plunge, the high-pressure air they push against find its way into the objects' pores and cracks, forcing their bodies apart from the inside," reports Quartz. "The result is a kind of detonation that looks like an explosion." From the report: To explain the astrophysics, researchers focused their work on a widely viewed February 2013 meteoroid explosion place over Chelyabinsk, Russia, a city of 1.1 million north of the Kazakhstan border. Researchers ran a computer program that allowed for them to simulate what happened to the meteoroid in the atmosphere. "Our simulations reveal a previously unrecognized process in which the penetration of high-pressure air into the body of the meteoroid greatly enhances the deformation and facilitates the breakup of meteoroids similar to the size of Chelyabinsk," the study states. The researchers added that while the air pressure is effective at breaking apart small meteoroids, larger ones would likely withstand the force as they come to Earth.

10 of 58 comments (clear)

  1. Missile Command by xxxJonBoyxxx · · Score: 3, Funny

    >> Why Meteoroids Explode Before Hitting the Earth

    I'm not saying it's Missile Command, but it's Missile Command.
    https://www.youtube.com/watch?v=nokIGklnBGY

  2. Re:Interstellar "Pull my finger Meteoroids" by Applehu+Akbar · · Score: 2

    So, aliens are basically bombarding us with meteoroids armed with the old "pull my finger" gag. The gall of them! Can't we build a space wall to keep these stinking meteoroids out?

    Dyson Corp. has sent Trump a proposal for building a space wall, but the cost would be in the quintillions of dollars. Just to fund a project of that size, we would have to cancel the F-35 program.

  3. Hang On... by ytene · · Score: 2, Interesting

    Something about the OP doesn't make sense.

    And no, not the fact that there isn't much in the way of "high-pressure air" at the outermost fringes of our atmosphere...

    The part which seems a little odd is to suggest that altering the apparent pressure [i.e. by the velocity of entry] can in some way "force" air into the cracks within a meteorite/meteorid to induce some form of break-up.

    Isn't it much more likely to be induced by the coefficient of expansion of the material concerned? If you take a meteorite and then flash-heat the outer surface very, very, very quickly - like for example by slamming it into an atmosphere at several thousand kph - then the outer layer will become very, very hot very quickly - and start to expand. The interior, meanwhile, simply won't have had time to warm up and thus will remain space-cold... As the outer layer warms, it expands. This would easily be enough to cause cracks in the material [think of the way that you can split a rock by pouring water into a crack and then waiting for the water to freeze...].

    It's been a while since I studied CFD [computational fluid dynamics - which is the science that would show how atmospheric gases would "flow" around an meteorite as it entered the atmosphere - but I think it's fair to say that a "boundary layer" would form that might in fact make it ridiculously difficult for "high pressure air" to be "forced" into tiny cracks in the surface.

    So... very interesting theory, but I think we might find that things like the irregular shape and density of the material [which causes non-uniform stress on the material] coupled with very high speed heating, might be significant factors too...

    1. Re:Hang On... by DrTJ · · Score: 2, Interesting

      You're on to something.

      As far as I know, there are two ways for something to explode (not merely "break up", or "burn"). Either the object is made out of a high explosive, in which the chemical reaction occurs faster than the disintegration, or there is a hard shell surrounding a "low explosive" which reacts "slowly" and builds up a pressure within the shell and explodes when the shell bursts.

      Clearly, the meteoroids are not made out of high explosives (I think and hope), but I have a hard time to view them as the other model either. It is not the internal that is heated - it is the outside. The pores and cracks in the "shell" would work to equalize the pressure difference, not create it. The heated gas in the cracks would would be of insignificant volume, and therefore contain negligible energy, and if even there were a process in which this gas would be trapped and cause cracks, it would be just that - cracks. It would not be an explosion disintegrating the meteoroid.

      Something is fishy. May be it is the model that they put into the computer... SISO.

    2. Re:Hang On... by burtosis · · Score: 3, Insightful

      Have you ever used a pressure washer? I own a mid grade entry level one with 3500 psi. You have to be very careful not to spray too hard into a crack or it will rip whatever it is apart. 3500 might not sound like a lot, but square area is deceptive. Say 300 psi gets into the crack, but the crack is 6 inches deep and 12 inches wide that's 21,600 lbs pushing on each side. But it gets worse, the stress has to flow from one side to the other of the crack, around the propagating crack tip. The sides of the crack act as a lever to concentrate the force many times higher if the crack tip is sharp and enough force is used to slightly bend the material. It's similar to fracking, the pressure may be moderate to high but the surface area is very large and it creates a super large force through several different effects that is capable of breaking rock.

    3. Re:Hang On... by careysub · · Score: 2

      It's been a while since I studied CFD [computational fluid dynamics - which is the science that would show how atmospheric gases would "flow" around an meteorite as it entered the atmosphere - but I think it's fair to say that a "boundary layer" would form that might in fact make it ridiculously difficult for "high pressure air" to be "forced" into tiny cracks in the surface.

      Try thinking of it this way.

      The meteor is stationary and it is being hit by a 20 km/s stream of gas (far into the hypersonic range, so this gas cannot "flow" around it). When the gas hits the surface of the meteor it comes to a dead halt. All that kinetic energy is converted into internal energy of the gas - extremely high pressure as well as extremely high temperature. This pressure at the very least exerts intense force on the meteor accelerating it (in this frame of reference) and subjecting it to powerful one-sided compressive force which deforms the body at the macro level, creating lateral tensile stresses. At the same time this high pressure gas is operating at the micro level, exerting pressure in every single pore and crack. Why do you imagine this is "ridiculously difficult" instead of the real case, which is "completely unavoidable"?

      What do you think this "boundary layer" is? A wall that keeps pressure from reaching the surface of the meteor? That is physically impossible simply due to conservation of momentum. Boundary layers on reentry bodies are simply cooler zones next to the surface of the body caused by ablation off of the surface. The pressure is exactly the same in the boundary layer as in front of it.

      --
      Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
    4. Re:Hang On... by crunchygranola · · Score: 3, Funny

      Something about the OP doesn't make sense. And no, not the fact that there isn't much in the way of "high-pressure air" at the outermost fringes of our atmosphere... The part which seems a little odd is to suggest that altering the apparent pressure [i.e. by the velocity of entry] can in some way "force" air into the cracks within a meteorite/meteorid to induce some form of break-up. Isn't it much more likely to be induced by the coefficient of expansion of the material concerned? If you take a meteorite and then flash-heat the outer surface very, very, very quickly - like for example by slamming it into an atmosphere at several thousand kph - then the outer layer will become very, very hot very quickly - and start to expand. The interior, meanwhile, simply won't have had time to warm up and thus will remain space-cold... As the outer layer warms, it expands. This would easily be enough to cause cracks in the material [think of the way that you can split a rock by pouring water into a crack and then waiting for the water to freeze...]. It's been a while since I studied CFD [computational fluid dynamics - which is the science that would show how atmospheric gases would "flow" around an meteorite as it entered the atmosphere - but I think it's fair to say that a "boundary layer" would form that might in fact make it ridiculously difficult for "high pressure air" to be "forced" into tiny cracks in the surface.

      Interesting how you imagine tossing around some dimly remembered terms like "boundary layer" invalidates the detailed physics of these researcher's model.

      If they had access to your brilliance they would have know the answer without even examining the problem!

      This should a Slashdot "law":

      "If, with just a few minutes of thought about a scientific topic you have only slight familiarity with, you believe you have identified a fatal error that a team of highly trained professional researchers have failed to detect, you can be certain that you are wrong."

      --
      Second class citizen of the New Gilded Age
  4. Re:Interstellar "Pull my finger Meteoroids" by GrumpySteen · · Score: 2

    Don't worry. Trump has assured everyone that he'll make the Martians pay for it.

  5. Re:Thermal Strain by mysticgoat · · Score: 2

    A meteor arriving with several times the Earth's escape velocity is not interacting with the atmosphere that you know; it it interacting with the plasma that is formed by compression in front of it. The streaks left by the sub-milimeter particles of a Leonid meteor shower are plasmas with a measured temperature of 4,000+ deg C; the plasma at the head of the meteor would be much hotter than that.

    So it is not cold air that is forced into the crevices of a meteor; it is very hot plasma. The pressure this exerts on the internal structure of the meteor is not countered by similar pressures on the back and sides of the object. Most meteors and bollides will burst apart.

  6. Re:FFS... They need to get out more... by crunchygranola · · Score: 2

    Are you always a cunt or is it just when you have anonymity?

    The un-self-aware irony in this is priceless.

    --
    Second class citizen of the New Gilded Age