[meteorite-list] Earth Impactors
From: EL Jones <jonee_at_meteoritecentral.com>
Date: Thu Apr 22 10:00:10 2004 Message-ID: <3D3F6EA5.D4D86385_at_epix.net> <!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> <body bgcolor="#FFFFFF"> Hello Walter, List <p>Thought provoking question for sure... <p>I am thinking it may be more of a question of how "small" must it be for pieces to survive in tact. Without specifics, I recall generally that objects over 1 meter don't lose all their cosmic energy before striking the surface. The larger the object the more retained cosmic energy. And as Rob said--Depends on what you call wide spread destruction. The best studied non asteroidal crater, I suppose, is Meteor Crater(sic)/Canyon Diablo(CD) Someone estimated the CD zone of destruction at 400 miles(640 km) in radius where most surface life was killed outright. <p>The higher the mass of the original meteoroid the more likely the impactor is to completely vaporize. Probably 99.9% of CD was "mistified " into iron droplets. The specimens recovered on the adjacent plane are thought to have shed off before impact. There are some from the crater rim that have distorted Widmanstätten lines and diamonds which would indicate great pressure but doesn't reveal conclusively if these were part of the swarm caught in the blowout or were at the rear of the disintegrating impactor. My recollection is that drilling operations encountered metal below the crater floor, but again we don't know if this was a core , fallback, or part of the shed of material which formed the swarm. I think Wolf Creek is the next smaller crater of recent age and I don't know anything of its history/research. <p>Clearly the size would have to be larger then Hoba to achieve destruction while survive in some semblance of its original form. Hoba, estimated at 60 tonnes, apparently did not disintegrate but did bury up around meters in solid limestone. ( figure out that crushing force -you construction engineers) Even this size didn't spald a substantial amount of adjacent rock to have caused local , little-alone wide spread, destruction. So my swag is bigger than a bread box and smaller than a soccer field. <p>Looking forward to hearing more answers on this. Keep in mind that my figures are old recollections and may not be wholly accurate. <br>Regards, <br>Elton <p>Walter Branch wrote: <blockquote TYPE=CITE><font face="Courier New"><font size=-1>"how large does an object have to be for it not to vaporize completely upon plunging through Earth's atmosphere, i.e., for there to be anything sizeable left to cause wide destruction once it hits the ground (or water)?"I know that the answer is not an easy one and there are numerous variables involved (e.g., type of material involved, angle of entry, definition of "wide destruction," etc.) but does anyone have a guess (or a SWAG) as to the answer.</font></font></blockquote> </body> </html> Received on Wed 24 Jul 2002 11:21:26 PM PDT |
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