Hello Count and Listers, Yes it would be intersting to see if something comes of this.You brought up something good when you said.....
"Particularly in the trading of micro-meteorites and smaller material." Now is that trading mirco meteorites that have TKW or mirco meteroites from taken from bigger meteorites? Shawn Alan [meteorite-list] (no subject) countdeiro at earthlink.net countdeiro at earthlink.net Sun Apr 4 11:43:15 EDT 2010 Previous message: [meteorite-list] "Meteorite and meteoroid: New comprehensive definitions" second part of the artical Next message: [meteorite-list] (no subject) Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] -------------------------------------------------------------------------------- Thanks Shawn, Excellent post. If accepted...these definitions will bring about a standardization in description that was sorely needed in some quarters. Particularly in the trading of micro-meteorites and smaller material. Count Deiro IMCA 3536 -----Original Message----- >From: Shawn Alan <photophlow at yahoo.com> >Sent: Apr 4, 2010 3:14 AM >To: meteorite-list at meteoritecentral.com >Subject: [meteorite-list] "Meteorite and meteoroid: New comprehensive >definitions" second part of the artical > >Hello List > >Here is the second part of the artical > >Meteorite and meteoroid: New comprehensive definitions > >by >Alan E. RUBIN1* and Jeffrey N. GROSSMAN2 > >1Institute of Geophysics and Planetary Physics, University of California, Los >Angeles, California 90095–1567, USA >2U.S. Geological Survey, 954 National Center, Reston, Virginia 20192, USA >*Corresponding author. E-mail: aerubin at ucla.edu >(Received 05 May 2009; revision accepted 14 September 2009) > > >There are more practical reasons that can be used >to select the best upper size cutoff for micrometeorites >and micrometeoroids. Meteorites have long been >recognized as rare, special kinds of rocks. The practice >of naming individual meteorites after the places where >they were found is based on this special status. >Generally, to receive a name, a meteorite must be well >classified and large enough to provide material for >curation and research. Much of the material that >forms meteorites in the inner solar system is relatively >coarse grained. Many chondrites and nearly all >achondrites and iron-rich meteorites have mineral grain >sizes that exceed 100 lm. Although in many cases it is >possible to classify small particles of meteoritic >material at least tentatively, this process is greatly >hindered when the particle size is significantly smaller >than the parental rock’s grain size. To allow for >proper classification, 2 mm is a more useful size cutoff >than 100 lm. In addition, the number of objects that >accrete to the Earth (and other bodies) varies >exponentially with the inverse of mass (e.g., Brown >1960, 1961; Huss 1990; Bland et al. 1996). Single >expeditions to recover micrometeorites have found >thousands of particles in the sub-millimeter size range >(Rochette et al. 2008), but very few that exceed 2 mm. >The 2 mm divide also seems to form an approximate >break between the smallest objects that have >historically been called meteorites and the largest >objects called micrometeorites. This leads to additional >refinements to our definitions: > >Micrometeorites are meteorites smaller than 2 mm in >diameter; micrometeoroids are meteoroids smaller >than 2 mm in diameter; objects smaller than 10 lm >are dust particles. > >By this definition, IDPs are particles smaller than >10 lm. We are not proposing a lower size limit for IDPs. >Before it impacted the Earth, object 2008 TC3 was >approximately 4 m across and was officially classified as >an asteroid (Jenniskens et al. 2009). It is likely that >when smaller interplanetary objects are observed >telescopically, they will also be called asteroids, even if >they are of sub-meter size. Thus, the boundary between >meteoroids and asteroids is soft and will only shrink >with improved observational capabilities. For the >minimum asteroid size. We thus differ from Beech and >Steel (1995) who suggested a 10 m cutoff between >meteoroids and asteroids. > >The Relationship between Meteorites and Meteoroids >It is tempting to include in our definition of >meteorite a statement that meteorites originate as >meteoroids, which, using our modified definition are >natural solid objects moving in space, with a size less that >1 m, but larger than 10 lm; this was done in previous >definitions such as that of McSween (1987). However, >because the Hoba iron meteorite is larger than 1 m >across, it represents a fragment of an asteroid, not a >meteoroid, under our definition of meteoroid. If a mass >of iron 12 m in diameter deriving from an asteroidal >core were to be found on Earth or another celestial >body, it would almost certainly be called a meteorite, >despite the fact that it was too large to have originated >as a meteoroid even under the Beech and Steel (1995) >definition. In addition, the Canyon Diablo iron >meteorites associated with the Barringer (Meteor) >Crater in Arizona, are fragments of an impacting >asteroid that was several tens of meters in diameter >(e.g., Roddy et al. 1980); the Morokweng chondrite may >be a fragment of a kilometer-size asteroid that created >the >70 km Morokweng crater in South Africa (Maier >et al. 2006). > >Comets, particularly Jupiter-family comets (JFCs), >could also produce meteorites. A small fraction of JFCs >evolve into near-Earth objects (Levison and Duncan >1997) and could impact main-belt asteroids at relatively >low velocities (approximately 5 km s)1) (Campins and >Swindle 1998). Meteorites could also be derived from >moons around planetary bodies. Lunar meteorites are >well known on Earth, and meteorites derived from >Phobos may impact Mars, especially after the orbit of >Phobos decays sufficiently (e.g., Bills et al. 2005). >We see no simple way out of this semantic >dilemma, so we add the refinement: > >Meteorites are created by the impacts of meteoroids >or larger natural bodies. > >Additional Complications >Fragments of Meteorites > >Meteorite showers result from the fragmentation of >a meteoroid (or larger body) in the atmosphere. In the >case of the L6 chondrite Holbrook, about 14,000 >individual stones fell (Grady 2000). Each of these stones >is considered a meteorite, paired with the others that >fell at the same time. A meteorite can break apart when >it collides with the surface of a body or it can fragment >at a later time due to mechanical and chemical >weathering. Each fragment of a meteorite is itself >considered a meteorite, paired with the other objects >that fell during the same event. > >Degraded Meteorites > >Weathering and other secondary processes on the >body to which a meteorite accretes can greatly alter >meteoritic material. Chondritic material has been >found embedded in terrestrial sedimentary rocks in >Sweden (e.g., Thorslund and Wickman 1981; Schmitz >et al. 2001). Other than the minor phase chromite (and >tiny inclusions within chromite), the primary minerals >in these extraterrestrial objects have been replaced by >secondary phases. Despite this extensive alteration, >some of these rocks (e.g., Brunflo) contain wellpreserved >chondrule pseudomorphs. Iron meteorites >can be severely weathered at the Earth’s surface, >forming a substance known as meteorite shale >(Leonard 1951) in which the original metal has been >completely oxidized; nevertheless, this material can still >preserve remnants of a Widmansta¨ tten structure. The >NomCom considers these types of materials to be >relict meteorites, defined as ‘‘highly altered materials >that may have a meteoritic origin. . .which are >dominantly (>95%) composed of secondary minerals >formed on the body on which the object was found’’ >(Meteoritical Society, 2006). Many relict meteorites >have received formal meteorite names in recent years. >We support the use of this terminology and would >further revise our definition as follows: > >An object is a meteorite as long as there is something >recognizable remaining either of the original minerals >or the original structure. > >We assert that objects that are completely melted >during atmospheric transit or weathered to the point >of complete destruction of all minerals and structures >should not be called meteorites. This would include >cosmic spherules (reviewed by Taylor and Brownlee >1991), ice meteorites that melted, and bits of what >appear to be separated fusion crust from larger >meteorites (eight of which have received formal >meteorite names from the NomCom as relict >meteorites, incorrectly in our opinion). A report of >possibly meteoritic material in sediments near the >Cretaceous ⁄ Tertiary boundary (Kyte 1998) presents a >borderline case. No primary minerals remain in this >object although the textures of secondary minerals are >suggestive of some kind of primary chondritic >structure. > >Meteorites accreted by their own parent body >We now consider whether it is possible for an >object to become a meteorite on the same celestial >body from which it was derived. For example, if >ejecta from a terrestrial impact crater lands back on >Earth, can it be considered a meteorite? Tektites are >widely held to be glass objects produced by large >impacts on Earth. Australite buttons were launched >on sub-orbital ballistic trajectories from their parent >crater and quenched into glass; they were partly >remelted on the way down when they encountered >denser portions of the atmosphere (e.g., Taylor 1961 >and references therein). Most researchers would likely >agree that these objects should not be considered >meteorites. However, if terrestrial ejecta reached the >Moon, we have argued that it should be considered a >terrestrial meteorite. The critical difference is that the >hypothetical material in the latter case escaped the >dominant gravitational influence of Earth, whereas >tektites did not. > >Material launched from a celestial body that >achieves an independent orbit around the Sun or some >other celestial body, and which eventually is re-accreted >by the original body, should be considered a meteorite. >The difficulty, of course, would be in proving that this >had happened, but a terrestrial rock that had been >exposed to cosmic rays and had a well-developed fusion >crust should be considered a possible terrestrial >meteorite. In a related context, Gladman and Coffey >(2009) calculated that large fractions of material ejected >from Mercury by impacts achieve independent orbits >around the Sun and are re-accreted by Mercury only >after several million years. Any of this material that >survived re-accretion could be considered a meteorite. >The next refinement of the definition of meteorite is >then: > >An object that lands on its own parent body is a >meteorite if it previously escaped the dominant >gravitational influence of that body. > >Relative sizes >As a final clarification, we suggest that: > >An object should be considered a meteorite only if it >accretes to a body larger than itself. > >REVISED DEFINITIONS OF METEORITE AND >METEOROID > >From the discussion above, new definitions of >meteorite and meteoroid are proposed: >Meteoroid: A 10 lm to 1-meter-size natural solid >object moving in interplanetary space. Meteoroids may >be primary objects or derived by the fragmentation of >larger celestial bodies, not limited to asteroids. >Micrometeoroid: A meteoroid between 10 lm and >2 mm in size. >Meteorite: A natural solid object larger than 10 lm >in size, derived from a celestial body, that was >transported by natural means from the body on which >it formed to a region outside the dominant gravitational >influence of that body, and that later collided with a >natural or artificial body larger than itself (even if it is >the same body from which it was launched). Weathering >processes do not affect an object’s status as a meteorite >as long as something recognizable remains of its >original minerals or structure. An object loses its status >as a meteorite if it is incorporated into a larger rock >that becomes a meteorite itself. >Micrometeorite: A meteorite between 10 lm and >2 mm in size. > >Interplanetary dust particle (IDP): A particle >smaller than 10 lm in size moving in interplanetary >space. If such particles subsequently accrete to larger >natural or artificial bodies, they are still called IDPs. >Acknowledgments—We thank our colleagues for useful >discussions and C. R. Chapman, P. Schweitzer, and >J. Mars for useful reviews. > >This work was supported in >part by NASA Cosmochemistry Grants NNG06GF95G >(A. E. Rubin) and NNH08AI80I (J. N. Grossman). >Editorial Handling—Dr. A. J. Timothy Jull > >REFERENCES >Armstrong J. C., Wells L. E., and Gonzalez G. 2002. >Rummaging through Earth’s attic for remains of ancient >life. Icarus 160:183–196. >Beech M. and Steel D. 1995. On the definition of the term >‘meteoroid’. 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Mineralogy of carbonaceous >chondrite clasts in HED achondrites and the Moon. >Meteoritics & Planetary Science 31:518–537. > >Shawn Alan >______________________________________________ >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 -------------------------------------------------------------------------------- Previous message: [meteorite-list] "Meteorite and meteoroid: New comprehensive definitions" second part of the artical Next message: [meteorite-list] (no subject) Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] -------------------------------------------------------------------------------- More information about the Meteorite-list mailing list ______________________________________________ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list [email protected] http://six.pairlist.net/mailman/listinfo/meteorite-list
