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From: Shawn Alan <photophlow_at_meteoritecentral.com>
Date: Sun, 4 Apr 2010 09:13:48 -0700 (PDT)
Message-ID: <719651.36980.qm_at_web113607.mail.gq1.yahoo.com>

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

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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

>

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>

>Shawn Alan

>______________________________________________

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