Tagish Lake

C2-ungrouped
Fell January 18, 2000
59° 42′ 15.7′ N., 134° 12′ 4.9′ E. Several hundred thousand fragments of this unique 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 fell at 8:43:43 A.M. onto ice-covered Tagish Lake, located between Atlin, British Columbia and Carcross, Yukon Territory. The 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 (magnitude ~–22), estimated to have been ~4 m in diameter and to have a pre-atmospheric weight of 56,000 kg (Brown et al., 2002), approached at a velocity of ~16 kilometers per second at an angle of 17.8°. Fragmentation models indicate that the object first exploded at an altitude of 34.4 km with an energy equivalent to 1.7 kT of TNT, which caused 88% fragmentation of the object; a total of 33 fragmentation events are thought to have occurred during descent (Ceplecha, 2007). At a height of 29.2 km, the 2,660 kg main massLargest fragment of a meteorite, typically at the time of recovery. Meteorites are commonly cut, sliced or sometimes broken thus reducing the size of the main mass and the resulting largest specimen is called the "largest known mass". entered the dark phase of its flight, its velocity now at 13.1 km/second. From models based on a 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 of 37–58% (ave. 40%, Hildebrand et al., 2006), it is estimated that ~1,300 kg of appreciable fragments fell to the ground, corresponding to a total ablationGradual removal of the successive surface layers of a material through various processes. • The gradual removal and loss of meteoritic material by heating and vaporization as the meteoroid experiences frictional melting during its passage through the atmosphere. The resulting plasma ablates the meteor and, in cases where a meteor loss of over 97%.

 

 

The multiple explosions and accompanying dust cloud were seen and heard by eyewitnesses, while a few others heard hissing associated with electrophonic sound phenomena, or noticed a metallic or sulfurous odor (Hildebrand et al., 2006). 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 was detected by seismic stations and U.S. Department of Defense satellites, providing data that has helped ascertain for the first time an accurate 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 (right) for a 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. The meteoroidSmall rocky or metallic object in orbit around the Sun (or another star). moved in a direction of 151.5° ± 2° with an elevation above the horizon of 17.8°. After calculating an orbit for this meteoroid, the aphelionPoint farthest from the sun in a body's elliptical orbit. was found to lie in the outer 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, possibly associated with the Apollo asteroid group—in particular, the low-albedo D-type asteroids and metamorphically related asteroids. There is a high probability that transfer to an Earth-crossing orbit occurred by means of the ν6 secular resonance. Excellent pictures of the event taken within two minutes of the explosion and spanning an extended time afterwards can be seen to the left. It shows the expanding smoke train of the Yukon meteor over a 14-minute period. The first frame shows a smoky red vapor trail just 1 minute and 30 seconds after the initial flash.

 

 

 

It was fortuitous that local resident and pilot, Jim L. Brook, had been previously briefed by meteoriticists from the University of Western Ontario on how best to collect meteoritic dust samples. At ~4:00 P.M. on January 25, 2000, while driving on the ice of the Taku Arm of Tagish Lake, Brook spotted black fragments on and within the snow and recognized them as meteorites. Over the next two days he collected several dozen fragments and fine particles totaling ~870 g, which were placed into clean Ziploc freezer baggies and kept frozen until they could be turned over to the scientists. Between April 20 and May 8, 2000, after the heavy snow cover had dissipated, search parties from the University of Calgary and The University of Western Ontario utilizing ATVs and snowmobiles identified and marked 412 additional fragment sites in situ, some situated deeply within the ice. Approximately 200 of these fragments were eventually collected before the ice lost its structural integrity. A few more pieces were recovered by local residents during the summer.

The photos below show various Tagish Lake fragments as they were found embedded in the ice. All photos courtesy of The University of Western Ontario and the University of Calgary.

 

 

 

 

 

 

 

The Tagish Lake strewnfield (left) covers an area of at least 16 × 4 km. The total recovered weight of this lightweight, friable 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 is 5 – 10 kg, but only a small fraction of that (~820 g) is being curated at the University of Alberta preserved in a frozen pristine state (Ralchenko et al., 2014).

Tagish Lake is among the most chemically primitive meteorites known, with a significantly higher carbonateMineral or compound containing carbon and oxygen (i.e. calcium carbonate, CaCO3, calcite). abundance than any other carbonaceous chondrite. It has undergone the most pervasive aqueous alteration of any C2 chondrite studied, and contains water and 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*. structurally bound in hydrated minerals, adsorbed onto 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 surfaces, and absorbed within the layers of smectite-group phyllosilicate clays, likely zones of prebiotic organicPertaining to C-containing compounds. Organic compounds can be formed by both biological and non-biological (abiotic) processes. synthesis (Garvie and Buseck, 2007). Bulk 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 porosity measurements of numerous Tagish Lake fragments reveal that the meteoroid had both a lower bulk density and a higher porosity than any other meteoroid similarly analyzed, with values very close to those of IDPs (Hildebrand et al., 2006). The composition of Tagish Lake can be separated into two isotopically distinct lithologies—a dominant carbonate-poor lithology, and a subordinate carbonate-rich lithology (Zolensky et al., 2002).

CARBONATE-POOR LITHOLOGY

The carbonate-poor lithology of Tagish Lake is composed of phyllosilicate-rich clasts (comprising µm- to sub-µm-sized mineral fragments) together with interspersed, aqueously altered, rimmed chondrules (mainly porphyritic and barred 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 types) enclosing small FeNi-metal inclusions. Other constituents present include anhydrous forsteritic olivine grains (mainly Fo99), lithic fragments of mainly 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). composition, framboidal 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., and sulfides (primarily 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 and 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), along with minor phosphides, chromiteBrownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups., spinel-rich spherules, and other rare refractory inclusionsInclusions found predominantly in carbonaceous chondrites and are rich in refractory elements particularly calcium, aluminum and titanium that in various combinations form minerals such as spinel, melilite, perovskite and hibonite. There are two types of refractory inclusion: • Ca Al-rich inclusions (CAIs) • Amoeboid olivine aggregates (AOAs) Refractory inclusions were.

 

Many of these constituents are enclosed by fine-grained, low-porosity rims composed of an unequilibrated assemblage 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, FeNi-sulfides, FeNi-metal, magnetites, low-Ca pyroxenes, and forsteritic olivines. It was demonstrated by Greshake et al. (2005) that these rims were accreted in the solar nebulaThe primitive gas and dust cloud around the Sun from which planetary materials formed.. However, Takayama and Tomeoka (2008) have invoked a 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. aqueous alteration process as the formation mechanism of these rims.

 

On a nm- to µm-scale, hollow, membrane-like globules composed of pristine 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.   carbon are present, attesting to a persistently cold environment since their formation before or during the formation of the Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. (Nakamura et al., 2003). All of these components are contained within a dense, fine-grained matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. of mostly Mg-rich saponite and 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 (likely greenalite), along with Fe–Ni sulfides. Only rare carbonates are present within this matrix in the form of polycrystalline calcium carbonate grains. Micropores are partially lined by these carbonates.

In the proposed alteration sequence of Greshake et al. (2005), which occurred on the parent body at very low temperatures (<100°C), olivine and metalElement that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn were replaced by phyllosilicates and pyrrhotites. Phyllosilicates also replaced Ca-rich phases in the rimmed objects, leading to the transport of Ca out of these objects by aqueous fluids and into the matrix component where carbonates were then precipitated. Subsequent oxidationOxidation 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 conditions resulted in the replacement of some pyrrhotite by magnetite. This was followed by the replacement of magnetite by the precipitation of fine-grained sulfides and the growth of carbonates. Thereafter, sulfur was incorporated into organic phases.

An alternative formation sequence was proposed by Takayama and Tomeoka (2012) to have occurred on the parent body. They discovered some unique clasts containing coarse-grained components lacking rims, along with attached matrix material, all of which have similar bulk chemical compositions, textures, and mineralogy. Based on their studies, they concluded that the present rim material that partially surrounds 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 and coarse-grained components is actually the remnant of a first-generation of matrix material from an earlier assemblage. They argue that, following a period of brecciationThe formation of a breccia through a process by which rock fragments of of various types are recemented or fused together., portions of this original assemblage (of chondrules, coarse-grained components, and matrix) were transported to another region and incorporated into a second-generation host matrix having a different bulk chemical composition, texture, and mineralogy. CARBONATE-RICH

LITHOLOGY

The carbonate-rich lithology is composed of very fine-grained phyllosilicates of mostly saponite, with only a very limited amount of fine-grained clasts, 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, and magnetite present. Whitish Fe–Mg–Ca–Mn carbonate grains are very abundant, and include calcite, dolomite, and breunnerite (formed in that sequence), while very little calcium carbonate occurs independently. The Fe–Mg–Mn carbonates, called sideriteAn obsolete term for an iron meteorite., likely replaced existing Ca carbonate grains through the percolation of fluids following impact fracturing. Micropores are completely lined by these carbonates. The carbonates display a wide range of compositions, some unknown from any other CI and 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, and exhibit heavy-oxygen 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. enrichment consistent with a high water/rock ratio (~2) more similar to CI than CM (~0.6) chondrites. Still, in comparison to the CI and CM groups, different components in Tagish Lake are not in isotopic equilibriumTerm used to describe physical or chemical stasis. Physical equilibrium may be divided into two types: static and dynamic. Static equilibrium occurs when the components of forces and torques acting in one direction are balanced by components of forces and torques acting in the opposite direction. A system in static.

In the proposed alteration sequence, which occurred on the parent body at higher temperatures (>300°C) than for the carbonate poor lithology, olivine and metal were replaced by phyllosilicates and magnetite, which were subsequently replaced by Ca carbonate. Following impact fracturing, siderite replaced some Ca carbonates, and coarse-grained sulfides were deposited. The estimated water/rock ratio during this phase is ~2. It may be assumed that the carbonate-rich lithology succeeded the carbonate-poor lithology.

Tagish Lake is a heterogeneous accretionary 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 that likely contains additional lithologies than the two outlined above. Newly identified probable lithologies include a carbonate-rich lithology in which siderite dominates over calcite, and an inclusion-poor lithology low in saponite-serpentine (with a corresponding presence of gypsum) and enriched in magnetite and sulfide (Izawa et al., 2010).

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. techniques and Mössbauer 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 have been used by Bland et al. (2004) to determine the modal mineralogy of several carbonaceous chondrites, including Tagish Lake, and to quantify the compositional range of the olivine phases (here its pure forsteritePure* magnesium end-member (Mg2SiO4) of the olivine solid solution series and an important mineral in meteorites. When magnesium (Mg) is completely substituted by iron, it yields the the pure Fe-olivine end member, fayalite (Fe2SiO4). The various Fe and Mg substitutions between these two end-members are described based on their forsteritic (Fo)). Ralchenko et al. (2014) determined the bulk and grain density and the porosity of Tagish Lake samples that had been maintained in their frozen pristine state. They utilized 3-D laser imaging (as opposed to the modified Archimedean glass bead method) and 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 pycnometry to determine the bulk volume and grain volume, respectively, and from these values they derived the porosity. The modal mineralogy (vol%) and other physical properties of Tagish Lake are as follows:

• • Olivine (forsterite, Fo100) — 7.0
  • Fe-Mg carbonate ————– 8.0
  • Pyrrhotite ———————— 5.3
  • Pentlandite ———————– 0.3
  • Magnetite ———————— 4.5
  • Saponite–serpentine ——— 71.2
  • TOTAL ———————— 100.0

 

• bulk density = 1.8 (±0.03) g/cm³
• grain density = 2.56 g/cm³
• porosity = 30 vol%

Tagish Lake has a high bulk carbon content of ~5.8 wt%, higher than CI chondrites and much higher than CM chondrites, with ~2.6 wt% of this carbon incorporated in organic components. The water-soluble organic component, which comprises only 0.01 vol% (much less than in CM chondrites), consists of mostly monocarboxylic and dicarboxylic acids, the former including the straight chain compound formic acid as has been found in the C2 chondrite EET 96029; all of these compounds could have formed by parent body or nebular processes. The remainder of the organic component (>99%) is present as insoluble C, which is predominantly composed of two high-molecular weight PAHs having an aromatic structure. This composition is in contrast to the mostly aliphatic-structured compounds of higher molecular weight found in CM chondrites. The insoluble organic matter in Tagish Lake contains a high proportion of diradicaloids among the aromatic moieties, which is considered to be a distinguishing characteristic of an extraterrestrial organic source (Binet et al., 2004). Since the most highly altered CI and CM group members also contain these same diradicaloids, this organic component must have been synthesized in the presolar nebular disk, and further discussions presented by Alexander et al. (2007) and by Quirico et al. (2012) suggest a possible origin in the interstellar mediumMaterial between the stars, consisting of gas, dust and cosmic rays (high energy charged particles moving at nearly the speed of light). It comprises ~10% of visible matter in the disk of our Galaxy (Milky Way). Until recently it was generally assumed that silicates in the ISM were amorphous, but.

All of the organic compounds present in Tagish Lake, including nitriles with low H content, are consistent with a low degree of aqueous processing following accretionAccumulation of smaller objects into progressively larger bodies in the solar nebula leading to the eventual formation of asteroids, planetesimals and planets. The earliest accretion of the smallest particles was due to Van der Waals and electromagnetic forces. Further accretion continued by relatively low-velocity collisions of smaller bodies in the of large interstellar molecules. The lower abundance of heavier organics in Tagish Lake compared to those in Murchison is evidence for lower alteration temperatures and lower degrees of chemical evolution on this asteroid. Consistent with these facts is the discovery of sub-µm-sized hollow spheres (‘nanoglobules’) first identified within the phyllosilicate matrix of Tagish Lake, which are composed of amorphous carbon that contains isotopically anomalous N and H. This component, perhaps associated with sheet silicates, is likely the major carrier of the isotopic anomalies (Zega et al., 2010). Abundances of anomalous N and H in this amorphous component in Tagish Lake are similar to those observed in interplanetary dust particlesExtremely small (~10 μm in diameter) particles found on Earth (or collected during high altitude flights) that are probably from outer space. Their small size poses a problem for most common chemical and petrographic analytical techniques and thus research into IDPs is marked by the application of new analytical procedures (IDPs), attesting to a primitive origin from icy dust particles. The presence of these nanoglobules infers that they formed in a cold molecular cloudAn interstellar gas cloud that is dense enough to allow the formation of molecules and comprised of a cold dense complex mixture of interstellar gas and dust roughly 75% hydrogen and 21-24% helium. Clouds contain trace amounts of other molecules, of which well over 100 different types have now been or in the outer parts of the protosolar disk, or alternatively, they accreted onto the Tagish Lake asteroid and were stored in a very cold environment (–253° to –263°C) over its entire history (see the PSRD article below). Notably, N has been found to be similarly incorporated as aromatic nitriles in Tagish Lake organic matter, in IDPs, and in cometary dust particles collected from 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. 81P/Wild 2 (Clemett et al., 2010).

The anhydrous component of Tagish Lake was studied and compared to that of the CM and CI chondrites (Simon and Grossman, 2003). Tagish Lake contains the silicateThe most abundant group of minerals in Earth's crust, the structure of silicates are dominated by the silica tetrahedron, SiO44-, with metal ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive polymerization and silicates are classified according to the amount of linking that occurs between the andradite, which is absent from CM meteorites, but it contains no tochilinite, which is abundant in CM meteorites. Tagish Lake contains primitive refractory forsterite grains, rare Fo-rich chondrules, and isolated olivine grains, the latter probably reflecting crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. within host chondrules and their subsequent fragmentation (Russell et al., 2010). This anhydrous component in Tagish Lake (~13 wt%) is much lower than that in CM chondrites (ave. 48 wt%), but higher than that in CI chondrites. Other features that were identified in both Tagish Lake and the CM group, but not in CI members, include hibonite-bearing and spinel-rich refractory inclusions, CAIs, and Cr- and Al-rich spinelMg-Al oxide, MgAl2O4, found in CAIs.. Furthermore, thick, fine-grained, accretionary dust mantles surrounding clasts and inclusions are found in Tagish Lake and the CM group, but have not been identified in any CI meteorites.

Phyllosilicates in Tagish Lake matrix and rims are predominantly Mg-rich saponite in contrast to the Fe-rich serpentines found in the CM group. This Mg-rich composition is likely due to the transfer of phyllosilicate Fe into magnetite. Notably, the unique chondrites MET 00432 (CM2), WIS 91600 (C2), and Bells (C2) have similar mineralogies to those of Tagish Lake (e.g., saponite and magnetite abundances), as well as similarities in O-isotopic composition and reflectance spectra; however, these meteorites have features suggesting that they experienced different degrees of aqueous alteration. It has been conjectured that these four carbonaceous chondrites may constitute a grouplet (Nakamura et al., 2009, 2013). In addition, the heated CM chondriteClass of carbonaceous chondrites named after the Mighei meteorite that fell in Ukraine in 1889. They represent samples of incompletely serpentinized primitive asteroids and have experience extremely complex histories. CM meteorites are generally petrologic level type 2 though a few examples of CM1 and CM1/2 also exist. Compared to CI PCA 91008 shows similarities to this potential grouplet. In their organic chemistry analyses, Yabuta et al. (2010) found that Tagish Lake and WIS 91600 have similar IOM contents and O-isotopic compositions, as well as certain spectral similarities, and it was suggested that these two meteorites may be genetically related. WIS 91600 shows evidence supporting a higher degree of aqueous alteration than in Tagish Lake, and unlike Tagish Lake it experienced short duration impact heating to <500°C.

Interestingly, Vernazza et al. (2010) report that both WIS 91600 and Tagish Lake have spectra that match the blue spectra of the bright Stickney craterBowl-like depression ("crater" means "cup" in Latin) on the surface of a planet, moon, or asteroid. Craters range in size from a few centimeters to over 1,000 km across, and are mostly caused by impact or by volcanic activity, though some are due to cryovolcanism. on Mars’ moon Phobos, but which do not match the remaining space-weathered (more red spectrum) regions of that moon. They raise the hypothesis that WIS 91600 and/or Tagish Lake may originate from the deeper and fresher material of that captured moon. Mid-infrared spectra of the martian moon Phobos acquired by the Mars Global Surveyor spacecraft indicate that both carbonates and desiccated phyllosilicates are present on its surface, consistent with the mineralogy of D-type asteroids and the Tagish Lake meteorite (Glotch et al., 2015).

Sulfides are present in greater abundance in Tagish Lake than in either the CI or CM group, although the range in sulfide phases is more similar to that in CM meteorites; still, a rosette morphology is found exclusively in Tagish Lake. The lower ratio of pyrrhotite to intermediate sulfides in Tagish Lake reflects a higher degree of aqueous alteration than that present in CM chondrites. In further contrast, no sulfate salts occur in Tagish Lake as they commonly do in CI chondrites. The magnetite abundance in Tagish Lake is similar to that in CI meteorites, but much higher than in CM members. The nitrogenPrincipal constituent of the Earth’s atmosphere (78.08 vol. % at ground level). Nitrogen is the fifth most abundant element in the universe by atom abundance. Nitrogen comprises only 3.5 vol. % of the atmosphere of Venus and 2.7 vol. % of Mars’s atmosphere. Nitrogen has two isotopes: 14N (99.632 %) and 15N content of Tagish Lake was determined to be 0.12 wt%.

In contradiction to the many CM-like primary features, Tagish Lake exhibits evidence of an alteration history more similar to that of the CI group (Russell et al., 2010). Both the bulk rock and the matrix O-isotopic composition of Tagish Lake are 16O-poor, with a plot located very close to the CI field following the 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 trend line above the TFL. The phyllosilicate O- and H-isotopic compositions of Tagish Lake are also similar to those of CI members, indicating similarities in both water composition and alteration temperature. Still, the anhydrous minerals O-isotopic composition range overlaps that of all carbonaceous chondrite groups. Moreover, 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 olivine O-isotopic composition is most similar to the CM and CV groups, and shows a positive correlation between 16O and Fo contents. Beyond that, the bulk H-isotopic composition of Tagish Lake is more like that of CR chondrites, with a much higher deuteriumAlso called heavy hydrogen, deuterium is an isotope of hydrogen (D, or 2H) whose nucleus contains one proton and one neutron. As a trace element formed during the nucleosynthesis epoch of the Big Bang, deuterium is an important indicator of the baryon density in the universe. The larger the density, the content than that measured in either CI or CM group members.

Neon- and N-isotopic studies of Tagish Lake indicate that interstellar grains (nanodiamonds, SiC, 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) are present in greater abundance than in other C2 chondrites. Isotopically anomalous Os has been identified in the carrier phase SiC in Tagish Lake, the first such finding ever reported (Humayun et al., 2005). This Os consists of a greater proportion of r-process (nucleosynthesis by rapid neutronCharge-neutral hadron with a mass of 1.6748 x 10-27 kg, equivalent to 939.573 MeV, and an intrinsic angular momentum, or spin, of ½ (in units of h/2π). The neutron is a nucleon, one of the two basic constituents of all atomic nuclei (apart from 1H, which consists of a single captures, as in 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) over s-process (nucleosynthesis by slow neutron captures, as in 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) osmium, and may reflect the preservation of presolar stardust that is typically heated and destroyed. In another case, primordial ratios of planetary 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. such as helium 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. have been found encapsulated within the three-dimensional form of carbon known as fullerene.

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 data, especially observed in a plot of Zn/Mn vs. Sc/Mn, indicate that Tagish Lake is a carbonaceous chondrite distinct from all others. Furthermore, both Raman and Fourier Transform Infrared Spectroscopic analyses of the carbonate-rich lithology have revealed that the carbonaceous component of Tagish Lake is unique from that of other carbonaceous chondrite groups (Djouadi et al., 2003). Results of a K–Ar age study conducted on bulk matrix samples of Tagish Lake by Turrin et al. (2014) indicate an isochron age of 2.51 (±0.03) b.y., or a corrected isochron age of 2.20 (±0.04) b.y. These investigators suggest that this young age may represent the time of arrival to the inner solar 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 where solar warming reset the Ar-based chronometer. A cosmogenic nuclideA nuclear species characterized by Z protons and N neutrons. analysis indicates that the Tagish Lake meteoroid had a relatively low CRE age of ~7.8 m.y. It experienced only low shock effects (S1) consistent with other C chondrites.

Based on mineralogy, petrologyScience dealing with the origin, history, occurrence, chemical composition, structure and classification of rocks., isotopic composition, bulk chemical composition, and organic chemistry, Tagish Lake shares some similarities with, but is unique from, both the CM and 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 groups. Based on Re–Os systematics and highly siderophile elementLiterally, "iron-loving" element that tends to be concentrated in Fe-Ni metal rather than in silicate; these are Fe, Co, Ni, Mo, Re, Au, and PGE. These elements are relatively common in undifferentiated meteorites, and, in differentiated asteroids and planets, are found in the metal-rich cores and, consequently, extremely rare on concentrations, an interesting scenario has been proposed by Brandon et al. (2005) in which Tagish Lake could have originated from a region overlying CI chondrites and underlying CM chondrites on a common parent body, with aqueous alteration increasing towards the interior. Others have suggested Tagish Lake may represent CI precursor material. On the other hand, studies of the large diversity of clasts present in the Kaidun chondrite breccia led investigators (MacPherson et al., 2009) to the conclusion that a near-continuum of carbonaceous chondrite objects exists, encompassing CR, CM, CI, and other similar precursor objects that experienced unique alteration histories—Tagish Lake is seen as the first representative of a new, evolutionarily distinct C2 carbonaceous chondrite object.

Tagish Lake is spectrally most similar to the D-class asteroids, as well as to the metamorphically related T- and P-type asteroids, the first such match ever made to these asteroid classes (although the Antarctic 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. WIS 91600 also shares these spectrographic characteristics). The D/T/P-class asteroids are mostly located in the outer belt region, consistent with the calculated orbital aphelion for Tagish Lake of ~3.3 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. One asteroid in particular, 308 Polyxo, exhibits almost identical visible and near-infrared reflectance spectra to that of Tagish Lake, and it also has a distinct 3-µm absorptionTransfer of energy to a medium as a particle or electromagnetic radiation passes through it. Absorption of electromagnetic radiation is the combined result of Compton scattering, σ, and photoelectric absorption, τ. It may be quantified: where, t = thickness, ρ = density, and μ = mass absorption coefficient, which combines Compton and photoelectric effects (μ = σ + τ). band like that in Tagish Lake (and in WIS 91600) indicative of the presence of hydrated minerals (T. Hiroi and S. Hasegawa, 2003). However, it was shown that there are other D-class asteroids besides 308 Polyxo located even closer to one of the Kirkwood GapsLack of asteroids in regions within the asteroid belt (between Mars and Jupiter) coinciding with orbital periods that are simple fractions of Jupiter’s own orbital period. The absence of asteroids in these gaps is due to resonance with Jupiter’s gravitational influence.        , from which an efficient transfer to Earth’s orbit could be executed. Nevertheless, the totality of the evidence raises the possibility that Tagish Lake could be derived from the D-class asteroid 308 Polyxo.

In a Cr-isotopic study of Tagish Lake, Luu et al. (2009) have found that it contains the highest 54Cr excess ever measured in a silicate fraction of a meteorite. This led them to describe Tagish Lake as the most pristine meteorite yet studied, even more so than CI chondrites, and they consider it likely that it was derived from either a comet or a D-class asteroid residing in the cold outer asteroid belt. A cometary origin for Tagish Lake has also been postulated by Bryson et al. (2018) based on paleomagnetic data, which they suggest indicates the acquisition by magnetite of a very low remanence (0.15 µT). This paleointensity is consistent with that estimated to have been present at a heliocentricCentered around a sun. Our own Solar System is centered around the Sun so that all planets such as Earth orbit around the Sun. Note that 25% of Americans incorrectly believe the Sun revolves around the Earth. distance of ~20 AU, and is similar to that measured for comet 67P. After formation, the Tagish Lake source body would have migrated to a storage orbit in the outer asteroid belt, possibly as a result of scattering during the final outward migration of the gas giants (‘Nice Model’).

Among D-class asteroids with similar reflectance spectra to Tagish Lake, 773 Irmintraud and 368 Haidea provide the best matches in the visible–near-infrared range. The fact that 773 Irmintraud is located closer to Jupiter’s 7:3 mean motion resonance than 368 Haidea is located to Jupiter’s 2:1 resonance may have a bearing on any associations. The D/T-class asteroid 308 Polyxo also has similar reflectance spectra to Tagish Lake in the visible–near-infrared range. Also noteworthy is the finding that 773 Irmintraud, 308 Polyxo, and the C-class asteroid 511 Davida all contain hydrated materials like those present in Tagish Lake. Data for this 3-µm hydrationReaction of a substance with water. band indicate that the closest match to Tagish Lake is 511 Davida (Hiroi et al., 2003). Further studies will be necessary to differentiate between these possible asteroid candidates.

Notably, parts of the martian moons Phobos and Deimos (trailing edge and leading edge, respectively) are spectrally D-class objects. The low bulk densitiesMass 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 calculated for these two moons are similar to that of Tagish Lake. The low densities determined for the martian moons are thought to represent macroporosity effects, calculated to be 25–45% for Phobos (Rosenblatt, 2011), which is consistent with the ~40% porosity calculated for Tagish Lake (Brown et al., 2001). In spite of this possibility, an origin for Tagish Lake in the outer asteroid belt remains a strong probability. Moreover, high-quality orbital Thermal Emission Spectrometer (TES) data obtained by the Mars Global Surveyor for Phobos demonstrate that mid-IR spectral features are inconsistent with the composition of Tagish Lake (Glotch et al., 2018). The TES data for Phobos does indicate the potential presence of a fine particulate basaltic component, which would support the hypothesis of a Mars impact origin for the two moons.

A small ‘CI1’ lithology previously found in Kaidun (a clast-rich carbonaceous chondrite) is reported to have an O-isotopic composition identical to that of Tagish Lake, and with a similar petrology as well. Besides that example, an unusual clastA mineral or rock fragment embedded in another rock. found in Tagish Lake is similar to another clast in Kaidun, one that was identified as a CM1. Furthermore, a number of phyllosilicate-rich micrometeorites that were recovered in Antarctica have mineralogies similar to the Tagish Lake carbonate-poor lithology. It has been argued by Izawa et al. (2010) that a continuum may exist, reflecting similarities in material components and variabilities in mineral modes, connecting the carbonaceous asteroids like Tagish Lake and comets. All of these independent clasts and micrometeorites present a valuable opportunity to increase our understanding of carbonaceous chondrite groups. The specimen of Tagish Lake shown above is a 0.24 g specimen showing the thin fusion crustMelted exterior of a meteorite that forms when it passes through Earth’s atmosphere. Friction with the air will raise a meteorite’s surface temperature upwards of  4800 K (8180 °F) and will melt (ablate) the surface minerals and flow backwards over the surface as shown in the Lafayette meteorite photograph below., and was exported from Canada under Cultural Property Export Permit #65152, August 3, 2000.

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For additional information on Tagish Lake, read the PSRD article by David W. Mittlefehldt: ‘Tagish Lake—A Meteorite from the Far Reaches of the Asteroid Belt‘, Dec 2002.

Another PSRD article by G. Jeffrey Taylor, ‘Organic Globules from the Cold Far Reaches of the Proto-Solar Disk‘, Jan 2007, examines the Taglish Lake meteorite and its distribution of sub-µm-sized, organic hollow globules.

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