OrgueilA large carbonaceous Ivuna-like (CI1) chondrite that disintegrated and fell in fragments near the French town of Orgueil on May 14, 1864. About 20 pieces, totaling ~12 kg in mass, were subsequently recovered from an area of several square km, some head-sized but most were smaller than a fist. Specimens Click on Term to Read More
Fell May 14, 1864
43° 53′ N., 1° 23′ E. This very rare carbonaceous chondriteCarbonaceous chondrites represent the most primitive rock samples of our solar system. This rare (less than 5% of all meteorite falls) class of meteorites are a time capsule from the earliest days in the formation of our solar system. They are divided into the following compositional groups that, other than Click on Term to Read More fell in France a few minutes after 8:00 P.M.. A luminous meteorHow long Sonic booms Of the several 10s of tons of cosmic material entering Earth's atmosphere each day, only about one ton reaches the surface. An object's chance of survival depends on its initial mass, speed and angle of entry, and friability (tendency to break up). Micrometeoroids radiate heat so Click on Term to Read More and sonic booms were followed by the fallMeteorite seen to fall. Such meteorites are usually collected soon after falling and are not affected by terrestrial weathering (Weathering = 0). Beginning in 2014 (date needs confirmation), the NomComm adopted the use of the terms "probable fall" and "confirmed fall" to provide better insight into the meteorite's history. If Click on Term to Read More of twenty stones; the largest stone was the size of a man’s head, but most were only fist-sized. The fall covered an area of over two miles², and the total recovered weight of this low-density meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and Click on Term to Read More is ~13 kg. This is the most chemically primitive of the meteorite classes, with near-solar ratios of elemental abundances. However, volatileSubstances which have a tendency to enter the gas phase relatively easily (by evaporation, addition of heat, etc.). abundances may represent an enrichment that occurred during aqueous alteration processes, rather than a preservation of primitive solar abundancesAmount of elements in the Sun as determined by spectral line intensities. Approximately 60 elements have been identified; the most abundant are listed in the table..
is a micro-regolith brecciaWork in Progress ... A rock that is a mechanical mixture of different minerals and/or rock fragments (clasts). A breccia may also be distinguished by the origin of its clasts: (monomict breccia: monogenetic or monolithologic, and polymict breccia: polygenetic or polylithologic). The proportions of these fragments within the unbrecciated material Click on Term to Read More
composed primarily of phyllosilicate aggregates consisting of intergrown serpentineName used for a large group of phyllosilicate minerals with the generalized formula X2-3 Y2 O5 (OH)4. Due to their various structures (meteoritics focuses primarily on (Fe, Mg)3Si2O5(OH)4), serpentine can be used to understand the chemistry and progress of aqueous alteration (hydration) of olivine, amphibole, or pyroxene dating back to Click on Term to Read More
and saponite measuring tens of nm to hundreds of µm in size and exhibiting significant chemical heterogeneity. An alteration sequence by which these aggregates may have formed was suggested by Morlok et al
(2006). They believe the initial lithology was a magnesian, coarse-grained aggregate (CGA) of phyllosilicatesClass of hydroxyl-bearing silicate minerals with a sheet-like structure. They result from aqueous alteration are dominantly serpentine and smectite in meteorites; found in the matrixes of carbonaceous chondrites. Phyllosilicates consist of repeating sequences of sheets of linked tetrahedra (T) and sheets of linked octahedra (O). The T sheet consists of Click on Term to Read More
, sulfides, magnetites, and carbonates. These components were then permeated by aqueous fluids over a period of ~15 m.y. to produce a fine-grained (<1 µm) aggregate (FGAa) matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. Click on Term to Read More
, which is enriched in Fe-bearing ferrihydrite comprising Fe dissolved from sulfides and magnetites (King et al.
(2015). Ultimately, continued alteration of this fine-grained material led to the elimination of most remnant mineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous Click on Term to Read More
inclusions resulting in increased abundances of Fe and other elements (FGAb). Other lithologies which are present include a CGA–FGA transitional lithology, a phosphate lithology (P possibly derived from precursor chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More
), and some anomalous lithologies.
Other end products resulted from extensive aqueous dissolution processes. Sulfates formed from S-rich solutions and were readily mobilized to enter into veins. CarbonateMineral or compound containing carbon and oxygen (i.e. calcium carbonate, CaCO3, calcite). Click on Term to Read More
grains were first dissolved and then recomposed to form initially dolomite, and then breunnerite—these have been precisely dated through the radiogenic isotopes of Cr and Mn (Hoppe et al.
, 2004, 2007; Petitat et al.
, 2011; Fujiya et al.
, 2011). An isochron was resolved spanning ~10 m.y., corresponding to a very early solar timeframe with an absolute age of 4.5635 (±0.0007) b.y. ago ending ~4.553 b.y. ago. These two carbonates plus calcite have variable isotopic compositions, and they were likely precipitated from an evolving low-temperature (26°C for dolomite to –6°C for breunnerite; Guo et al.
, 2007) aqueous fluid that was primarily mobilized by impact heating, but residual heat from the decay of radioactive 26
Al and 60
Fe was probably also a contributor. MagnetiteFe oxide, Fe2+Fe3+2O4, containing oxidized iron (Fe3+) found in the matrix of carbonaceous chondrites and as diagnostic component in CK chondrites. In CK chondrites, magnetite is typically chromian, containing several wt. % Cr2O3. Click on Term to Read More
was also formed through aqueous alteration processes at temperatures of up to 150°C. An I–Xe age was determined to be 4.5604 b.y. (Hohenberg et al
Chondrules are not present in Orgueil, although the small abundance of olivineGroup of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion Click on Term to Read More
that is observed likely represents material from disaggregated remnant chondrules. This absence of chondrules reflects either a characteristic at the time of formation or is a result of later aqueous alteration (Macke et al.
, 2011). Only a single aqueously altered CAISub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they Click on Term to Read More
has been identified in the least altered CI chondriteRare meteorite class named after the Ivuna meteorite that fell in Tanzania in 1938. They are among the most primitive, friable (crumbly), and interesting of all meteorites, having undergone extensive aqueous alteration. They lack chondrules and CAIs as a result of this alteration, but contain up to 20% water, as Click on Term to Read More
Ivuna (Frank et al.
, 2011), but presolar grainsMineral grains that formed before our solar system. These tiny crystalline grains are typically found in the fine-grained matrix of chondritic (primitive) meteorites. Most grains probably formed in supernovae or the stellar outflows of red giant (AGB) stars before being incorporated in the molecular cloud from which the solar system Click on Term to Read More
of graphiteOpaque form of carbon (C) found in some iron and ordinary chondrites and in ureilite meteorites. Each C atom is bonded to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons. The two known forms of graphite, α (hexagonal) and β (rhombohedral), have Click on Term to Read More
, diamondOne of the naturally occurring forms of carbon found in meteorites. Each C atom is bonded through covalent sp3 hydrid orbitals to four others. The strength of the C-C bonds makes diamond the hardest naturally occurring substance (according to the Mohs scale) in terms of resistance to scratching. There are Click on Term to Read More
(the highest content known), corundumCrystalline form of aluminium oxide, Al2O3, found in Ca-Al-rich inclusions (CAIs). Corundum-bearing CAI are a rare class of high-temperature condensates from the inner regions of the protoplanetary disk1. Click on Term to Read More
, silicon-carbide, chromium-oxide, and FeNi-sulfide do occur, as well as a new Mg–Al–Cr mineral. Utilizing Raman spectroscopyTechnique of splitting electromagnetic radiation (light) into its constituent wavelengths (a spectrum), in much the same way as a prism splits light into a rainbow of colors. Spectra are not smooth but punctuated by 'lines' of absorption or emission caused by interaction with matter. The energy levels of electrons in
and a microprobe, the latter measuring the isotopes of interstellar grains at a size range ≤500 atoms, it was discovered that some high-density crystalline graphite grains and some low-density, glassy, kerogen-type carbonElement commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. diamond*; b. graphite*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. amorphous carbon; h. carbon nanotube*. Click on Term to Read More
grains present in Orgueil contain highly anomalous C-, Ca-, and Ti-isotopic compositions. These findings suggest a derivation of the graphite and kerogen-type carbon grains from stellar objects such as low-metallicity AGB starsStars on the Asymptotic Giant Branch, which represents a late stage of stellar evolution that all stars with initial masses < 8 Msun go through. At this late stage of stellar evolution, gas and dust are lifted off the stellar surface by massive winds that transfer material to the interstellar Click on Term to Read More
and Type II supernovae, respectively (Jadhav et al.
, 2007, 2010; Wopenka et al.
, 2011). Other regions have been identified in certain meteorites including Orgueil that contain 54
Cr-rich grains, likely carried by nanoscale spinelMg-Al oxide, MgAl2O4, found in CAIs.
particles (Qin et al.
, 2010). This 54
Cr isotopeOne of two or more atoms with the same atomic number (Z), but different mass (A). For example, hydrogen has three isotopes: 1H, 2H (deuterium), and 3H (tritium). Different isotopes of a given element have different numbers of neutrons in the nucleus. Click on Term to Read More
anomaly was heterogeneously distributed throughout the protoplanetary diskFlattened and rotating disk of dense gas and dust/solids orbiting a young star from which planets can eventually form. Click on Term to Read More
, and evidence favors an injection of these grains as well as others through a late Type II supernovaStellar explosion that expels much or all of the stellar material with great force, driving a blast wave into the surrounding space, and leaving a supernova remnant. Supernovae are classified based on the presence or absence of features in their optical spectra taken near maximum light. They were first categorized Click on Term to Read More
event. Observed variability of 54
Cr among the different meteorite classes suggests that the supernova dust contamination occurred during the active formation of the solar protoplanetary disk.
The low-Ni sulfide pyrrhotiteIron sulfide group of minerals whose composition ranges widely between its end members pyrrhotite (Fe7S8) whose crystal structure is monoclinic, and troilite (FeS) whose crystal structure is hexagonal. Its general formula is Fe1−xS (where x = 0 to 0.17). The troilite phase is found mainly in meteorites and in the Click on Term to Read More
present in Orgueil is also found in the other CI meteorites. It has been suggested that low-temperature alteration of primary troiliteBrass colored non-magnetic Fe sulfide, FeS, found in a variety of meteorites.
produced both pyrrhotite and magnetite. It was reported that Orgueil and Ivuna contain higher abundances of both magnetite and carbonate as well as Ni-enriched pyrrhotite, and that the pyrrhotite contains less pentlanditeFe-Ni sulfide, (Fe,Ni)9S8, that is often associated with troilite, and found in the matrix and chondrules of CO, CV, CK and CR chondrites. The color is yellow-bronze with light bronze-brown streak and metallic luster. It typically forms during cooling of magmatic sulfide melts during the evolution of parent silicate melt. The Click on Term to Read More
, all features which are consistent with a higher degree of alteration than that in other CI-group members. The finer-grained phyllosilicate present in Orgueil suggests that it experienced the highest degree of aqueous alteration (King et al.
, 2015). Contrariwise, the presence of ferrihydrite in both Orgueil and Alais but not in Ivuna may indicate a lower degree of aqueous progression in Ivuna. These consistently distinct petrographical and mineralogical features found among the CI members have prompted Bullock et al.
(2003, 2005) to propose a division of the CI group based on degree of aqueous alteration as follows: 1) Orgueil and Ivuna experienced an extended period of aqueous alteration in which acidic hydrothermal fluids completely dissolved pentlandite, and 2) Alais and Tonk (and probably Revelstoke) experienced a shorter alteration period resulting in the preservation of some pentlandite. Eventually, dissolved Ni was deposited within the matrix of Orgueil and Ivuna; some Ni was combined with Na to form the sodium nickel sulfate, Ni-bloedite, whereas other Ni formed ferrihydrite.
A study of CI chondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More
representing both falls (Orgueil, Alais, and Ivuna) and finds (Y-82162 and Y-980115) was conducted by King et al.
(2014) in which they measured modal abundances and employed X-ray diffractionAnalytical technique used to determine the structures of crystalline solids. A monochromatic beam of X-rays (usually Cu-Kα) is diffracted off repeating planes of atoms in crystalline samples to produce a diffraction pattern. Through analysis of the diffraction pattern, atomic structures can often be determined.
and IR spectroscopy analyses. Compared to the CI falls, they found that the CI finds contain less phyllosilicate with higher olivine and sulfide abundances (see diagram below). In addition, significant differences were observed in the IR spectra for the two groups, and they attributed all of these differences to greater degrees of thermal metamorphism among the CI finds. Temperatures for the finds reached 500–750°C compared to only ~150°C for the falls. Moreover, the heavier O-isotopic composition of the finds was found to be consistent with mass-dependent fractionationConcentration or separation of one mineral, element, or isotope from an initially homogeneous system. Fractionation can occur as a mass-dependent or mass-independent process. Click on Term to Read More
associated with thermal metamorphism. They argue that the duration of heating on the CI parent bodyThe body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. Click on Term to Read More
, on the order of hours to several years, is more consistent with an orbital perigee very close to the SunOur parent star. The structure of Sun's interior is the result of the hydrostatic equilibrium between gravity and the pressure of the gas. The interior consists of three shells: the core, radiative region, and convective region. Image source: http://eclipse99.nasa.gov/pages/SunActiv.html. The core is the hot, dense central region in which the
(<0.1 AUThe astronomical unit for length is described as the "mean" distance (average of aphelion and perihelion distances) between the Earth and the Sun. Though most references state the value for 1 AU to be approximately 150 million kilometers, the currently accepted precise value for the AU is 149,597,870.66 km. The Click on Term to Read More
) rather than radiogenic or impact heating.
Diagram credit: King et al.
, National Institute of Polar Research, Fifth Symposium on Polar Science – Antarctic meteorites (2014) X-ray diffraction techniques and Mössbauer spectroscopy have been used by Bland et al.
(2004) to determine the modal mineralogy of several carbonaceous chondrites including Orgueil. They were also able to quantify the compositional range of the olivine phases. In addition, the grain densityMass of an object divided by its volume. Density is a characteristic property of a substance (rock vs. ice, e.g.). Some substances (like gases) are easily compressible and have different densities depending on how much pressure is exerted upon them. The Sun is composed of compressible gases and is much Click on Term to Read More
can be readily estimated from the mode data, and therefore, in combination with the calculated bulk density, the porosityThe volume percentage of a rock that consists of void space. Vesicular porosity is a type of porosity resulting from the presence of vesicles, or gas bubbles, in igneous rock such as the pumice presented here. Vesicular porosity is very rare in meteorites and is often associated with slag, one Click on Term to Read More
can be determined. The modal mineralogy (vol%) of Orgueil is as follows:
- Fo100 ————– 2.1
- Fo80 —————- 2.6
- Fo60 —————- 1.1
- Troilite ———————- 1.2
- Pyrrhotite —————— 2.7
- Magnetite —————— 5.1
- Serpentine —————– 7.7
- Saponite–serpentine — 73.8
- Ferrihydrite ————– 3.7
- TOTAL —————– 100.0
- grain density = 2.43 g/cm³
- bulk density = 1.58 g/cm³
- porosity = 35 vol%
The composition for Orgueil (along with Ivuna and Alais) was also determined by King et al. (2015) utilizing X-ray diffraction. They found the average modal composition of Orgueil to be 83% phyllosilicate (serpentine/saponite), 6.7% magnetite, 5.7% sulfide, 3.3% ferrihydrite, 1% olivine, and 0.3% gypsum (of probable terrestrial origin), and that it may also contain <1% dolomite.
Bland et al.
(2004) found that an inverse correlation exists for the olivine and the phyllosilicate phases. It is presumed that the saponite–serpentine was formed by the aqueous alteration of primary anhydrous olivine. White veins of Mg- and Ca-sulfate (epsomite and gypsum, respectively) were not present in Orgueil or the other CI1 meteorites when original examinations were performed shortly after they fell. Rather, the veins are likely the result of the hygroscopic nature of CI1 meteorites. Terrestrial atmospheric water absorbed during their residence on Earth has mobilized existing sulfates to produce the white veins, which coincidentally has affected both the measured porosity and total water content of these meteorites. On the other hand, organicPertaining to C-containing compounds. Organic compounds can be formed by both biological and non-biological (abiotic) processes. Click on Term to Read More
carbon–phyllosilicate assemblages present in Orgueil and other CI chondrites have been shown to be primary constituents that are the product of aqueous alteration on the parent body; these assemblages may have served as catalysts for the formation of more complex organic molecules (Garvie and Buseck, 2007).
Current studies suggest that both cometary dust and meteorites should be produced from the disruption of Jupiter-family comets which originate in the Kuiper beltRegion in the outer solar system beyond Neptune's orbit that contains billions of small, icy planetesimals from the original protoplanetary disc that failed to coalesce into planets. The Kuiper Belt extends from Neptune's orbit at 30 AU to ~55 AU. It is ~20x wider and 20-200x more massive than the Click on Term to Read More
. Studies have shown that Antarctic micrometeorites have a similar carbonaceous chondriteChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More
:ordinary chondriteWork in Progress Ordinary chondrites (OCs) are the largest meteorite clan, comprising approximately 87% of the global collection and 78% of all falls (Meteoritical Society database 2018)1. Meteorites & the Early Solar System: page 581 section 6.1 OC of type 5 or 6 with an apparent shock stage of S1, Click on Term to Read More
ratio (~7:1) as the composition of zodiacal dust (M.M.M. Meier, 2014). Based on observational evidence and current modeling, it is thought that comets should be dark in color and should have a low density and strength, a high porosity, a solar ratio of elements, an elevated ratio of C, H, O, and N, a high interstellar grain content, anhydrous and highly unequilibrated silicates, few to no chondrules, and a low cosmic-ray exposure ageTime interval that a meteoroid was an independent body in space. In other words, the time between when a meteoroid was broken off its parent body and its arrival on Earth as a meteorite - also known simply as the "exposure age." It can be estimated from the observed effects Click on Term to Read More
(<10 m.y.). An early formation beyond the snowline would be consistent with accumulated ices and radiogenic elements such as 26
Al, which would produce heating and aqueous alteration features.
Orbital data obtained from several carbonaceous chondrites (e.g.
, CI Orgueil [eyewitness plotting]; CMs Maribo and Sutter’s Mill [instrument recording]) are a good match to the orbits expected from the disruption of Jupiter-family comets, but are unlike the orbits of ordinary chondrites and most other asteroidal objects (M.M.M. Meier, 2014). Both the orbital eccentricityThe deviation of an orbit from circularity. Circles have eccentricities of 0. Click on Term to Read More
and semimajor axis for Maribo is nearly identical to those of CometConglomeration of frozen water and gases (methane, ammonia, CO2) and silicates that that formed in the outer solar system and orbits the Sun. In recent years, the description of comets has shifted from dirty snowballs to snowy dirtballs with more dust than ice. However, the ratio is less than 10-to-1. Click on Term to Read More
Encke and the associated Taurid swarm of objects (Haack et al.
, 2011). Both the CI and CM groups of meteorites exhibit characteristics that are consistent with the descriptions in the previous paragraph. Consistent with a cometary origin, Orgueil contains only a few amino acids, mainly alpha- and beta-alanine, glycine, and gamma-amino-n
-butyric acid (the smallest gamma-amino acid found in meteorites). These amino acids are considered to be products of very low temperature conditions (<150°C) such as might be found on an extinct comet in the asteroid beltBelt located between 2.12 and 3.3 AU from the Sun and located between the orbits of Mars and Jupiter containing the vast majority of asteroids. The asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such Click on Term to Read More
(Botta et al.
, 2007), or having derived from limited precursor components such as hydrogenLightest and most common element in the universe (~92% by atoms; ~75% by mass). Hydrogen's isotopes are: • 1H (99.9885 %) • 2H (0.0115 %), also called deuterium. • 3H, also called Tritium, is a radioactive (t½ = 12.32 y) by-product of atmospheric thermonuclear tests in Earth's hydrosphere and atmosphere. Click on Term to Read More
cyanide, ammonia, and carbonyl compounds (e.g.
, formaldehyde, acetaldehyde, and acetone)—constituents identified in several comets. The high abundance of aliphatic amines (primarily methylamine and ethylamine) present in Orgueil may be the result of decomposition (decarboxylation) of their corresponding amino acids during extensive aqueous alteration (Aponte et al.
, 2015). The type specimen of the CI group, Ivuna, was also found to contain similar extraterrestrial amino acids in similar abundances to those of Orgueil. The CRE age of Orgueil is also quite short, calculated to be ~5 m.y., and is within the expected survivability window for a meteoroidSmall rocky or metallic object in orbit around the Sun (or another star).
derived from a Jupiter-family comet which was inserted into an Earth-crossing orbitThe elliptical path of one body around another, typically the path of a small body around a much larger body. However, depending on the mass distribution of the objects, they may rotate around an empty spot in space • The Moon orbits around the Earth. • The Earth orbits around Click on Term to Read More
Analysis of seven fragments, recovered from three aerogelSilicon-based solid with a porous, sponge-like structure in which 99.8% of the volume is empty space. Aerogel is used to collect high velocity particles without damaging them and also is used to insulate the electronics of the Mars rovers. Aerogel is 1,000 times less dense than glass and has many Click on Term to Read More
tracks obtained through NASA’s Stardust missionSpace mission to study Comet Wild 2 (see http://stardust.jpl.nasa.gov/home/index.html). During the encounter, Stardust performed a variety of tasks including making counts of particles encountered by the spacecraft and real-time analyses of the compositions of these particles and volatiles. It also captured cometary particles using Aerogel and stored them for return
to comet Wild 2, revealed an average composition similar to the bulk composition of CI chondrites (Stephan et al.
, 2007). Examples of low-temperature (150–200°C) aqueous alteration phases found in both comet Wild 2 and Orgueil include the nickel-, copper-, and zinc-bearing iron sulfides cubanite, pyrrhotite, pentlandite, and sphalerite (Berger et al.
, 2011, 2015). Olivine in both Orgueil and Ivuna has a similar compositional range to that found in comet Wild 2 particles as well as in anhydrous IDPs, and less similar to other carbonaceous chondrite types (Le Gac et al.
, 2009). Besides the CI meteorites, there exists some C-rich aggregates in clasts and inclusions within some unequilibrated ordinary chondrite breccias that closely fit a cometary profile. Meteorites with such inclusions include Sharps (H3.4), Dimmitt (H4), Tsukuba (H5–6), and Krymka (LL3.1). In their research on micrometeoroid/microxenolith populations originating from both comets and asteroids, Briani et al.
(2011) determined that two distinct populations could not be resolved. Therefore, they concluded that a continuum may exist between carbonaceous asteroids and comets.
Notably, based on mineralogical analyses by King et al.
(2015), three thermally metamorphosed (Stage III of Nakamura, 2005) CI-like chondrites—Y-82162, Y-86029, and Y-980115—are considered to possibly represent a separate parent body, perhaps one of the known NEOs such as 3200 Phaethon. The specimen of Orgueil shown above is a 0.162 g specimen measuring approximately 5 mm in diameter. A more representative photo of Orgueil can be seen on the website of the Muséum National d’Histoire de Paris
. Fall of Orgueil—Engraving Published 1865 in l’Annuaire Mathieu
Image credit: Gounelle and Zolensky, MAPS
, vol. 49, #10, p. 1773 (2013) ‘The Orgueil meteorite: 150 years of history’