CM2.0/2.1 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 (Yamakawa and Yin, 2013) Genomict RegolithMixture of unconsolidated rocky fragments, soil, dust and other fine granular particles blanketing the surface of a body lacking an atmosphere. Regolith is the product of "gardening" by repeated meteorite impacts, and thermal processes (such as repeated heating and cooling cycles). 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 (with thermally metamorphosed (dehydrated) and Tagish Lake-like components) Photo taken by Lisa Warren in Reno, Nevada Fell April 22, 2012 38° 48′ 14′ N., 120° 54′ 29′ W. On Earth Day 2012, April 22 at 7:51 A.M., a fireballA fireball is another term for a very bright meteor, generally brighter than magnitude -4, which is about the same magnitude of the planet Venus as seen in the morning or evening sky. A bolide is a special type of fireball which explodes in a bright terminal flash at its end, often with visible fragmentation. accompanied by a sonic boom was seen, heard, and even smelled by local residents as it streaked over California and Nevada moving in a generally western direction. As the approximately 70-ton, 3-m-sized object reached an altitude of 48 km at a speed of 28.6 (±0.7) km/second, it exploded with the release of energy equivalent to an ~4-kiloton explosion (Jenniskens et al., 2012). Fragments of ‘black gold’ fell within a strewn fieldArea on the surface containing meteorites and fragments from a single fall. Also applied to the area covered by tektites, which are produced by large meteorite impacts. Strewnfields are often oval-shaped with the largest specimens found at one end. Given that the largest specimens go the greatest distance, a meteoroid's encompassing the towns of Lotus and Coloma, including the location of the first discovery of California gold in 1848 at Sutter’s Mill.
Two days after 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, the first charcoal-colored stone weighing 5.5 grams was recovered by 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 hunter Robert Ward. Utilizing NEXRAD high-resolution Doppler weather radar data, along with seismic data, Marc Fries of the Planetary Science Institute constructed a more accurate map of the inferred strewn field. Because of rather strong winds aloft blowing towards the ENE, the approximately 4 × 2 mile strewn field has been depicted curving slightly to the north reflecting the drift of smaller, lighter fragments. Models predict that the largest fragments weighing perhaps 10–20 kg would have landed ~19 miles farther west of the known strewn field (Fries et al., 2012). A heliumHelium (He) Second lightest and second most abundant element (after Hydrogen) in the universe. The most abundant isotope is 4He (99.9998%), 3He is very rare. Helium comprises ~8% of the atoms (25% of the mass) of all directly observed matter in the universe. Helium is produced by hydrogen burning inside airship was employed by scientists from NASA and the SETI Institute to search for possible impact features, but none were reported. Over the next few weeks, meteorite hunters and locals together spent thousands of manhours searching the rattlesnake and poison oak infested strewn field collecting numerous small fragments. The largest single findMeteorite not seen to fall, but recovered at some later date. For example, many finds from Antarctica fell 10,000 to 700,000 years ago. weighing in at 205.2 g was made by Jeffrey Grant. Although many remain unofficially recorded, nearly 100 Sutter’s Mill fragments have been recovered having a combined weight of over 1,000 grams.
A consortium of investigators led by Dr. Peter Jenniskens of the SETI Institute has begun the long process of analysis and classification. Initial characterization of Sutter’s Mill conducted at Johnson Space Center by M. Zolensky (2012) indicated that this is a 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 breccia showing many petrological similarities to CM 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. Sutter’s Mill was described as a highly comminuted regolith breccia by Kebukawa et al. (2013), consistent with the wide variety of components present in the matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. and the presence of solar-wind-implanted noble gasesElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive.. Matrix components include 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 similar in size to those in CM2.5 Murchison, isolated lithic fragments, aggregates of forsteritic 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 and low-Ca pyroxeneA class of silicate (SiO3) minerals that form a solid solution between iron and magnesium and can contain up to 50% calcium. Pyroxenes are important rock forming minerals and critical to understanding igneous processes. For more detailed information, please read the Pyroxene Group article found in the Meteoritics & Classification category., abundant CAIsSub-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, grains of the sulfides 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, 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, and oldhamiteMn-Ca sulfide, (Mn,Ca)S, is a pale to dark brown accessory mineral found in minor amounts in highly reduced meteorites such as many enstatite chondrites, and some aubrites and enstatite achondrites. Oldhamite in enstatite chondrites likely formed by solar nebular gas condensation. CaS Oldhamite was also found in the most fresh (CaS), and rare FeNi-metal; the low abundance of the latter being attributed to seismically-driven gravitational sorting/settling by Zolensky et al. (2013). The presence of oldhamite and Fe-Ni-Cr phosphides in Sutter’s Mill attests to the impact fragmentation of an E chondrite or aubriteAubrites are named for the Aubres meteorite that fell in 1836 near Nyons, France. They are an evolved achondrite that is Ca-poor and composed mainly of enstatite (En100) and diopside (En50Wo50) with minor amounts of olivine (Fa0) and traces of plagioclase (An2-8). They contain large white crystals of enstatite as (A. Rubin, UCLA), or alternatively, the oldhamite could have been formed during the dehydration process at temperatures of at least ~750°C as outlined by Haberle et al. (2013), or during impact-generated heating to >300°C as suggested by Beck et al. (2013).
Ott et al. (2013) found that 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 was present in an abundance of ~471 to ~1460 ppmParts per million (106)., indicating the possible admixture of a ureilite component, while a lower limit was calculated for a presolar SiC content in Sutter’s mill of 3.8 (±0.4) ppm. Analyses of specimen SM2-5 by Kebukawa et al. (2014) led to their discovery of two relatively large diamond grains, considered to be xenolithic in origin, and to have likely formed through a chemical vapor depositionMethod for growing solids in which a gaseous precursor (containing fragments of the desired solid) is decomposed and deposited onto a desired surface. Chemical Vapor Deposition (CVD) is one of the most powerful synthetic methods in material science due to its remarkable flexibility. A variety of surfaces can be coated, (CVD) process on a large 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.. In addition, Haberle et al. (2013) reported finding bluish-white grains within the matrix that have been identified as the first occurrence of portlandite (Ca(OH)2), thought to be a product of reductionOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons, while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants of CaSO4 catalyzed by CO and CO2. Utilizing X-ray micro-tomography, Tsuchiyama et al. (2014) have found ubiquitous µm-scale solid inclusions present in all calcite grains studied, and they identified one calcite grain that likely harbors an ~2 µm-sized remnant spherical fluid inclusionFragment of foreign (xeno-) material enclosed within the primary matrix of a rock or meteorite. incorporating a bubble with a solid particle inside. However, due to the small size of the bubble it could not be ascertained if it contains an aqueous fluid.
Advanced analyses of numerous Sutter’s Mill samples were conducted at the Center for Meteorite Studies (L. Garvie, 2013), leading to the conclusion that there are two distinct mineralogical classes present—one is rich in olivine and the other is rich in amorphousMaterial without the regular, ordered structure of crystalline solids. Amorphous substances, like glass, lack a definite repeating pattern in their atomic structures (crystallinity). There may be small regions of order, but, overall there is disorder. clays. The olivine-rich (75–80 wt%) material exhibits characteristics akin to the Belgica-group of thermally metamorphosed CM chondrites, while the clay-rich material is considered to be a strong match to the C2-ungrouped Tagish Lake. It was proposed that both of these disparate classes of chondritic material were independently incorporated into the Sutter’s Mill parent object, itself characterized as a rubble pile.
A detailed study of Sutter’s Mill by Beauford et al. (2012, 2013) revealed that it is a complex regolith breccia consisting of a primary accretional matrix containing two dominant clastA mineral or rock fragment embedded in another rock. lithologies present in approximately equal abundances in variable combinations and in breccia-in-breccia clasts, attesting to a history of impact mixing and regolith recycling. One clast type is a dark-colored chondrule-rich lithology (CRD) and the other is a light-colored chondrule-poor lithology (CPL), with the components of each expressing a different degree of aqueous alteration. Other minor lithologies reported include sub-mm-sized dark inclusions (DI), carbonate-rich clasts, and a xenolithic component consisting of enstatiteA mineral that is composed of Mg-rich pyroxene, MgSiO3. It is the magnesium endmember of the pyroxene silicate mineral series - enstatite (MgSiO3) to ferrosilite (FeSiO3)., oldhamite, and phosphides likely derived from E chondrites or aubritesAubrites are named for the Aubres meteorite that fell in 1836 near Nyons, France. They are an evolved achondrite that is Ca-poor and composed mainly of enstatite (En100) and diopside (En50Wo50) with minor amounts of olivine (Fa0) and traces of plagioclase (An2-8). They contain large white crystals of enstatite as (Zolensky et al., 2014).
Similar to the dust mantles prevalent around other CM components, dark, fine-grained rims are present on many of the coarse-grained objects in Sutter’s Mill. These rims are considered likely to have formed and hardened during impact compaction processes, but they might be accretionary rims developed in the nebulaAn immense interstellar, diffuse cloud of gas and dust from which a central star and surrounding planets and planetesimals condense and accrete. The properties of nebulae vary enormously and depend on their composition as well as the environment in which they are situated. Emission nebula are powered by young, massive, or possibly the result of a combination of both of these formation processes (Haack et al., 2012). These fine-grained rims were investigated by Beauford and Sears and it was found that their presence is limited to those primary CRD lithologies that experienced only limited aqueous alteration, and that their formation was restricted to the period prior to comminution and evolution of the CM regolith.
Nagashima et al. (2012) found that O-isotopic compositions of olivine from type-I and type-II chondrules and AOAs plot along the CCAM line, and they identified abundant coarse dolomite and calcite grains, the latter having O-isotopic compositions nearly identical to calcites in CM chondrites. Major and trace elementSubstance composed of atoms, each of which has the same atomic number (Z) and chemical properties. The chemical properties of an element are determined by the arrangement of the electrons in the various shells (specified by their quantum number) that surround the nucleus. In a neutral atom, the number of analyses of three separate samples were consistent with those of CM chondrites (Yin et al., 2012; Friedrich et al., 2012). Grady et al. (2012) studied the abundance and isotopic composition of 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*. and argonNoble gas represented by the atomic symbol Ar, that has Z = 18, and an atomic weight of 39.948. It is colorless, odorless, and very inert gas, comprising ~1 % of the Earth's atmosphere. by stepped combustion in a Sutter’s Mill sample and found close similarities to carbonaceous chondrites, with the closest match demonstrated for C2-ung Tagish Lake. O-isotopic measurements conducted by Kohl et al. (2013) of acid-washed Sutter’s Mill material, thus eliminating carbonateMineral or compound containing carbon and oxygen (i.e. calcium carbonate, CaCO3, calcite).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 influence, led them to conclude that aqueous alteration increased the water/rock ratio and shifted the three-isotope plot away from the CCAM line towards the TFL.
Like CM chondrites, Sutter’s Mill is a breccia containing features indicative of both weak aqueous alteration and thermal metamorphism to 500–750°C affecting the chondruleRoughly 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 olivinemesostasisLast material to crystallize/solidify from a melt. Mesostasis can be found in both chondrules, in the matrix around chondrules, and in achondrites as interstitial fine-grained material such as plagioclase, and/or as glass between crystalline minerals. . Some clasts have been heavily aqueously altered to subtype 2.0, resulting in the replacement of some chondrule constituents with the 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 Fe-cronstedtite/tochilinite + Mg-serpentine (A. Rubin, UCLA). Notably, Howard et al. (2009) have argued that the phyllosilicate abundances among CM chondrites are within a few percent of each other, and thus reflect similar aqueous alteration processes. Other clasts (e.g., SM2-5, thought to represent a comminuted regolith breccia) exhibit secondary heating features consistent with Stage III, based on the scale of Nakamura (2005) (Zolensky et al., 2014). In these clasts, phyllosilicates have been converted to fine-grained olivine, tochilinite has been converted to troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites., and carbonates have been destroyed. See the Murchison page for further details on classification based on thermal metamorphism.
Cooper and Jenniskens (2012) and Dillon et al. (2013) measured soluble organicPertaining to C-containing compounds. Organic compounds can be formed by both biological and non-biological (abiotic) processes. compounds in Sutter’s Mill and identified mono-carboxylic acids (e.g., formic acid and acetic acid) typically present in significant abundances in many CM chondrites; they were present in much lower abundances than in Murchison. In addition, large abundances of soluble inorganic compounds were found, particularly sulfate, which is common to CM chondrites. Using advanced methods to characterize soluble organic compounds, Schmitt-Kopplin et al. (2012) found that they were present in comparatively low abundances, comprising highly oxygenated species or organometallic compounds. An organic C component was determined to reside in both hollow and filled, 15N-rich nanoglobules that likely formed in the cold solar or presolar nebula (Nakamura-Messenger et al., 2013). They also observed that the constituents in the relatively anhydrous matrix component of Sutter’s Mill were mineralogically similar to the matrix of Acfer 094, a unique carbonaceous chondrite tentatively classified as a subgroup of the CO chondrites; Simon and Grossman, 2015). Utilizing X-ray 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 in a study of specimen SM2-5, Kebukawa et al. (2014) determined that the matrix organic matter has a lower N/C ratio compared to other carbonaceous chondrites.
Pizzarello et al. (2012) determined that amino acids were scarce in Sutter’s Mill, and that they contain low-complexity hydrocarbons, mainly naphthalene. Analyses by Glavin et al. (2012, 2013) of both pre- and post-rain samples also revealed lower C2–C5 amino acidA small molecule containing and amine group (–NH2) at one end and a carboxylic acid group (–COOH) at the other. They link up with various other amino acids to form proteins. Because they are used to build proteins, most of the human body consists of amino acids with their abundance second abundances (~660–9,500 ppbParts per billion (109).) compared to those in Murchison (~14,000 ppb). Similarly, analyses of one of the most pristine Sutter’s Mill specimens (SM2) by Burton et al. (2012) found a 20 × lower abundance of amino acids than measured in Murchison. These low levels are considered likely the result of significant parent body aqueous alteration and/or thermal (>150°C) metamorphism. Advanced infrared analyses by Flynn et al. (2013) indicated the presence of carbonates and associated organic matter. This organic matter consists in large part of aliphatic hydrocarbons, and it was determined to be compositionally different from organic matter identified in Murchison, but consistent with the type identified in Tagish Lake.
CT scans conducted at AMNH (Ebel et al.) provided 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 and 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 data for two Sutter’s Mill samples. From these it was determined that Sutter’s Mill has a bulk density of 2.23 g/cm³. Similarly, bulk density and grain density measurements were made by Britt et al. (2012) using conventional methods. The bulk density for one sample was determined to be 2.31 g/cm³; all sample density values are within the range of those for CM chondrites. A measurement of porosity showed that it is relatively high at 31 (±1.4) %, also similar to typical values for CM chondrites. Likewise, the magnetic susceptibility value is within the range for CM chondrites. Results of reflectance spectroscopy performed by Grady et al. (2013) was consistent with a CM classification.
An analysis of Mn–Cr systematics in Sutter’s Mill calcite and dolomite revealed a resetting of this chronometer ~4.563 b.y. ago, while a more recent resetting event within 1 b.y. ago was evident in the Re–Os systemDefinable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with (Walker et al., 2013 and references therein). The ε54Cr value for Sutter’s Mill calculated by Yamakawa and Yin (2013) is identical to that of Murchison, indicating an origin for both meteorites from the same precursor. Similarly, the secondary carbonate mineral dolomite was utilized by Jilly et al. (2014) for Mn–Cr radiometric dating in Sutter ’s Mill. This short-lived (half-lifePeriod of time required for 50% (½) of the atoms of a radioactive nuclide in a sample to decay. After two half-lives, 25% ( ½ x ½ = 1/4) of the original radioactive nuclide will remain. After three half-lives, 12.5% ( ½ x ½ x ½ = 1/8) of the original radioactive nuclide will remain. = 3.74 m.y.) chronometer is well suited for that purpose in that Mn becomes sequestered in the precipitating carbonate, while Cr remains with the percolating aqueous fluid. This creates a measurable excess of 53Cr through the in situ decay of radioactive 53Mn, a value which is temporally related to the onset of secondary carbonate formation during aqueous alteration. This age for carbonate formation was determined to be 4.5637 (+0.001.1/–0.001.5) b.y., or 2.34–5.26 m.y. after CV3 CAIs, which is an absolute age anchored to the U-corrected Pb–Pb age of the D ’Orbigny angriteType of evolved achondrite meteorite that represent some of the earliest stages of asteroidal differentiation and magmatism in our solar system. Angrites are named for the Angra dos Reis meteorite, which fell in Rio de Janeiro, Brazil, in early 1869. They are basaltic (mafic) rocks, often containing porous areas, and. Their study showed that carbonate formation occurred relatively early in Sutter’s Mill, as well as in other carbonaceous chondrite groups—a result of aqueous processing sustained by radiogenic heating of accreted ices.
Noble gasElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. studies conducted by Hamajima et al. (2012) and Ott et al. (2013) established a very young CRE age for Sutter’s Mill that defines the low end of the range for the CM2 chondrite group (previously exhibiting two major peaks at 0.2 and 2.0 m.y.), reflecting a relatively recent ejection from its parent body ~19–51 t.y. ago. Cosmogenic radionuclideRadioactive isotope - Atomic nuclide that decays radioactively . studies conducted by Nishiizumi et al. (2014) provide a similar very young CRE age of 82 (±8) t.y. Another noble gas study of Sutter’s Mill was conducted by Okazaki and Nagao (2017). Based on 21Ne and the estimated shielding depths of the samples, they calculated a CRE age of 59 (± 23) t.y. In a broad study of cosmogenic radionuclides in Sutter’s Mill and in a large number of CM group members, Nishiizumi et al. (2013) detected several major collisional clusters representing a mixture of both petrologic types 1 and 2. The pre-atmospheric size of the Sutter’s Mill meteorioid was also calculated by Nishiizumi et al. (2013, 2014), and it was demonstrated to have been a minimum of ~1 m in diameter based on a bulk density of 2.3 g/cm³, which is consistent with the estimate of 1–2 m based on other parameters.
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. Studies have shown that Antarctic micrometeorites have a similar carbonaceous chondrite: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, 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 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 (<10 m.y.). Both the CI and CM groups of meteorites exhibit characteristics which are consistent with the above descriptions.
Orbital data obtained from several carbonaceous chondrites (e.g., the 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, asOrgueilA 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 [eyewitness plotting] and the CM chondrites 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. 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. Encke and the associated Taurid swarm of objects (Haack et al., 2011). On the other hand, a CRE age study of CM chondrites conducted by Meier et al. (2016) shows a possible relationship exists to the asteroid breakup event ~8.3 m.y. ago that formed the Ch/C/Cg-type members of the Veritas family. In addition to the large abundance of 3He-enriched interplanetary dust discovered in 8.2 m.y.-old deep-sea drill cores, ~1/6 of all CM meteorites have 21Ne-based CRE ages that are consistent with derivation from this catastrophic breakup, while others with significantly younger CRE ages could represent secondary collisions among the Veritas fragments.
Fragments from many Sutter’s Mill samples were generously donated to the University of Arizona and other institutions where studies will be conducted in preparation for the upcoming carbonaceous asteroid sample return mission, OSIRIS-REx. The 0.053 g specimen shown above is a portion from stone #SM14, as listed in Jeniskens’ official NASA database, a stone that impacted the garage door of Suzanne Matin and broke into fragments weighing together 11.5 g. A BBC News video captured the actual recovery of portions of this stone, and also features meteorite hunter Mike Farmer searching the strewn field with fellow hunters as he discusses the significance of this rare fall.
The photo above shows the broken fragments of a stone that impacted a parking lot, which were immediately recovered by Dr. Peter Jenniskens.
An X-ray computed tomography video of Sutter’s Mill 18. The image resolution is 14 micron/voxel and the field of view is ~2 × 3 cm². Courtesy of Yin Lab at UC Davis. note: reload page to repeat this video