[meteorite-list] What makes a meteor glow?
From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Mon, 28 Jun 2010 19:46:52 -0500 Message-ID: <7C9FFD39393F45B39B60B4A313A98A36_at_ATARIENGINE2> Bob, Phil, List, The entire process is degrading kinetic and potential energy into --- at the end --- heat, through which all that energy is dissipated. "Ablative loss" includes energy released as "light" of various frequencies, but the principle reason for so much mass to be lost (90%+) is good, old-fashioned combustion. The atmosphere functions like a gigantic blowtorch being fed with oxygen blowing at incredible velocity on a very hot object. (There's no difference between the case where the object moves and the air stands still and where the air moves and the object stands still; it's all relative.) If you could construct an oxygen-nitrogen jet with 30-40 Mach speed and direct it at a stationary object, the target would heat up and burn exactly like a meteroid/meteorite does. What's left over? Well, the combustion products: tiny smoke-like particles of oxides of all the elements heated hot enough to oxidize (and tiny smoke-like particles of all the elements that won't oxidize). Even some of the nitrogen in the air forms compounds if the thing is hot enough. And naturally all that energy release heats the air surrounding the event but the principal source of light in the "streak" behind a meteor is produced by "burning" or oxidizing the material. In so energetic an event, every pathway for energy to degrade is utilized: heating, oxidation, ionization, re-radiation, re-combination, and so forth. The event changes as it proceeds. In very thin air at very high speeds (like an annual shower meteor), the quantity of oxygen is limited and radiative effects predominate. It is harder to dissipate energy those ways, so a tiny cometary particle produces a streak that's brighter, thicker and more persistent than its small combustion trail. At lower altitudes and lesser speeds, combustion is the dominant way of releasing and dissipating the energy. Meteoroids/meteorites that leave a thick, pronounced "trail" (like Carancas did) are combustion-dominated events. The deeper the meteoroid bores into the atmosphere, the greater the supply of oxygen. (In the case of Carancas, the thick opaque "smoke" was said to have followed the object all the way to the ground!) Is anything left? Well, when you cut the size of a particle down to half, you lose 7/8ths of the mass, but only 3/4rs of the frontal area, so the mass loading against the atmosphere is halved. There's less friction and less energy released. Keep on halving the size, and you end up with tiny micron-sized particles that are quickly cooled and slowed to a standstill, as meteoritic dust particles -- extra-terrestrial "smoke." Your question made me think: what if the Earth's atmosphere had NO oxygen? I suppose if you had an atmosphere of say, argon, you would still have a luminous streak produced entirely by radiative processes. It would last longer, like a high altitude cometary particle, all the way down and possibly more of the meteoroid would survive. (So, if you're ever on a planet with an argon atmosphere, keep an eye out.) On the other hand, if a planet had an atmosphere with fluorine in it (not likely, but possible), there'd just be a sudden brilliant flash and -- Poof! No more meteor. Same goes to a lesser degree for atmospheres with chlorine or even bromine (all unlikely). Sterling K. Webb -------------------------------------------------------------------------------- ----- Original Message ----- From: "Bob King" <nightsky55 at gmail.com> To: <meteorite-list at meteoritecentral.com> Sent: Monday, June 28, 2010 3:09 PM Subject: [meteorite-list] What makes a meteor glow? > Hi everyone, > This thread has perhaps appeared before, but I can't seem to find a > clear answer on how much an incoming meteor's light is due to heating > of the material itself versus the recombination of ionized atoms that > have been heated by the object's movement through the air. I always > thought the majority portion -- the bright streak -- was a tube-like > glow of ionized air. > Thank you for your help on the question :) > Bob > ______________________________________________ > Visit the Archives at > http://www.meteoritecentral.com/mailing-list-archives.html > Meteorite-list mailing list > Meteorite-list at meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list Received on Mon 28 Jun 2010 08:46:52 PM PDT |
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