Some reports indicate that the deeply cold-soaked main mass of the 104 kg Colby, WI, L6 -- which was recovered quickly after its witnessed fall on a warm and very humid July 4 in 1917 -- actually acquired a coating of frost within minutes of being excavated.
Mark ----- Original Message ----- From: "Graham Ensor via Meteorite-list" <[email protected]> To: "MEM" <[email protected]> Cc: [email protected] Sent: Wednesday, June 29, 2016 2:29:43 AM Subject: Re: [meteorite-list] Hot vs Cold again...wasmMeteorite Crashes Through Thailand House Roof Elton...I agree with most of that....but the cooling starts straight after hot flight miles up where the air temperature is around -30 -50 deg...surely any heat in the fusion crust would dissipate very quickly up there and then the interior temperature would then equalize to bring it down to well below freezing as it free-falls with minimum friction to change that....so my thinking is that even the fusion crust would also be very cold on landing unless somehow the friction from punching the hole heats the surface briefly...but I doubt that it would last more than a fraction of a second. Graham On Wed, Jun 29, 2016 at 2:04 AM, MEM via Meteorite-list < [email protected] > wrote: This was looked into several times in the list history. I am recalling details from those discussions/my research. Any body arriving from space is at least -60°c and closer to -120°c to -180°c based on some black body studies of asteroids-- IIRC The temperature at the air-meteoroid boundary of entry exceeds the melting point of both iron and olivine. Most of that heat is carried off as an iron/silicate mist. Each mili-second of incandescent flight an entirely new surface is formed. Inward traveling heat is being stripped away almost as fast as it is penetrating in low thermo-conducivity but much faster in high conductivity bodies (e.g iron). The radiative cooling during dark flight is probably calculable and a missing factor in estimating the state of heat content upon landing. One of the Weston CT meteorites formed a frost rind shortly after falling after sufficient time for all reentry heat to dissipate. I do not recall any other comments. This was discovered by a fireman under the dining table. I do not recall which other meteorite it was but, another was noted to have a frost rind after a few minutes. Other falls such as Sylacaga are silent as to the temperature. Conclusions: An immediately-recovered, newly-fallen silicate/stony meteorite is usually--but briefly "hot/uncomfortably warm" to the touch. The rind is very hot but lacks much heat reservoir. Heat penetration--based on measuring heated rims-- is somewhere between 2mm but not more than 6mm. Beyond 6mm does not get above 140° F proven by the domain reset of magnetite orientation in Martian Meteorites. Be it remembered that an empty .50 cal brass case "feels" like it would burn you if it goes down one's shirt but lacks the heat content to cause burns. Specific characterizations of hot/warm are hidden among the various accounts of some well known falls nearby humans. Monahans, Mbale, Allende, Murchison etc.. If you disagree-- don't start some silly list fight--Do your own weeks of research reach your own conclusions! Iron meteorites owing to a high coefficient of therm-conductivity are likely very hot to the touch and warm throughout. It is probably much like a piece of metal cut by a welding torch--no sign of bluing but very hot on the opposite end of the cut. Elton
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