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At least 55 records · Page 3

Tarda and Tagish Lake: Samples from the same outer Solar System asteroid and implications for D- and P-type asteroids

Here, we report a comprehensive study of the ungrouped type 2 carbonaceous chondrite, Tarda, which fell in Morocco in 2020. This meteorite exhibits substantial similarities to Tagish Lake, Wisconsin Range 91600, and Meteorite Hills 00432, which are generally considered to have originated from a D-type asteroid(s). We constrain the compositions and petrologies of the materials present in a potential sample of a D-type asteroid by reporting the petrography, bulk chemical compositions, bulk H, C, N, Cr, and Ti isotopic compositions, reflectance spectra, and in situ chemical compositions of metals, sulfides, carbonates, and FeO-poor and FeO-rich chondrule silicates of Tarda. We also present new data for Tagish Lake. We then compare Tarda with the other Tagish Lake-like meteorites. Tarda and Tagish Lake appear to be from the same parent body, as demonstrated by their similar petrologies (modal abundances, chondrule sizes), mineral compositions, bulk chemical and isotopic compositions, and reflectance spectra. While the two other Tagish Lake-like meteorites, Wisconsin Range 91600 and Meteorite Hills 00432, show some affinities to Tagish Lake and Tarda, they also share similar characteristics to the Mighei-like carbonaceous (CM) chondrites, warranting further study. Similarities in reflectance spectra suggest that P-type asteroids 65 Cybele and 76 Freia are potential parent bodies of Tarda and the Tagish Lake-like meteorites, or at least have similar surface materials. Since upcoming spacecraft missions will spectrally survey D-type, P-type, and C-type Trojan asteroids (NASA's Lucy) and spectrally study and return samples from Mars' moon Phobos (JAXA's Martian Moons eXploration mission), which is spectrally similar to D-type asteroids, these meteorites are of substantial scientific interest. Furthermore, since Tarda closely spectrally matches P-type asteroids (but compositionally matches the D-type asteroid like Tagish Lake meteorite), P-type and D-type asteroids may represent fragments of the same or similar parent bodies.

58 GEOSCIENCES↗

Formation and interior evolution of Mars

The formation and earliest evolution of Mars involved core formation followed by magma ocean solidification and primordial crust formation. Here, in this study, we review the formation and early interior evolution of Mars as understood through meteorite studies. Martian meteorites exhibit ages that span the entire history of the Solar System, but most derive from compositionally distinct sources that formed early in the history of Mars. Geochemical and isotopic studies of Martian meteorites have provided critical information on Mars’ building blocks, bulk composition, and its differentiation into a core, mantle and crust. Radiogenic isotope systems provide vital insights into the petrogenesis of Martian meteorite source regions and into the nature and timescales of primordial differentiation on Mars. Application of short-lived isotope chronometers to Martian meteorites indicates that the Martian core formed early within <10 million years (Ma), while magma ocean differentiation and crust formation occurred soon thereafter, within the first tens of Ma of Solar System history. Bulk silicate Mars is variably depleted in moderately volatile elements relative to chondrites, but to a lesser extent than the Earth. The nature and evolution of more volatile elements and volatile species on Mars (e.g., H 2 O, C, S, halogens) remains an active area of investigation, but overall suggest that Mars is more enriched in volatile elements than the Moon but less than the Earth. While geochemical exploration of Mars coupled with new discoveries of Martian meteorites has provided a wealth of information, the compositional and lithologic diversity on Mars significantly exceeds that seen in the suites of Martian meteorites currently studied. This implies that our current perspective on the planet's evolution is very likely biased, highlighting the need for future sample return missions to Mars.

Kruijer, Thomas S.↗

Two Strengths of Ordinary Chondritic Meteoroids as Derived from Their Atmospheric Fragmentation Modeling

The internal structure and strength of small asteroids and large meteoroids is poorly known. Observation of bright fireballs in the Earth’s atmosphere can explore meteoroid structure by studying meteoroid fragmentation during the flight. Earlier evaluations showed that the meteoroid’s strength is significantly lower than that of the recovered meteorites. We present a detailed study of atmospheric fragmentation of seven meteorite falls, all ordinary chondrites, and 14 other fireballs, where meteorite fall was predicted but the meteorites, probably also ordinary chondrites, were not recovered. All observations were made by the autonomous observatories of the European Fireball Network and include detailed radiometric light curves. A model, called the semiempirical fragmentation model, was developed to fit the light curves and decelerations. Videos showing individual fragments were available in some cases. The results demonstrated that meteoroids do not fragment randomly but in two distinct phases. The first phase typically corresponds to low strengths of 0.04–0.12 MPa. In two-thirds of cases, the first phase was catastrophic or nearly catastrophic with at least 40% of mass lost. The second phase corresponds to 0.9–5 MPa for confirmed meteorite falls and somewhat lower strengths, from about 0.5 MPa, for smaller meteoroids. All of these strengths are lower than the tensile strengths of ordinary chondritic meteorites cited in the literature, 20–40 MPa. We interpret the second phase as being due to cracks in meteoroids and the first phase as a separation of weakly cemented fragments, which reaccumulated at the surfaces of asteroids after asteroid collisions.

79 ASTRONOMY AND ASTROPHYSICS↗

Onset of magma ocean solidification on Mars inferred from Mn-Cr chronometry

The mantle of Mars probably differentiated through the crystallization of a magma ocean during the first tens of million years (Ma) of Solar System evolution. However, the exact timescale of large-scale silicate differentiation of the martian mantle is debated, and in particular, it remains unclear when differentiation commenced. In this paper, we applied the short-lived 53 Mn- 53 Cr system to martian meteorites in order to date the onset of large-scale mantle differentiation on Mars. The new Cr isotope data demonstrate that martian meteorites exhibit no resolvable radiogenic 53 Cr variations, and instead have a uniform +20.2±1.2 (95% conf.) parts-per-million excess in 53 Cr/ 52 Cr relative to the terrestrial mantle. The investigated groups of martian meteorites are lithologically varied and derive from diverse mantle sources that probably had variable Mn/Cr. Hence, the lack of 53 Cr variability among martian meteorites demonstrates that silicate differentiation on Mars occurred after the extinction of 53 Mn. Provided that the sources of the martian meteorites have Mn/Cr variations that are typical of the terrestrial planets, this result implies that the onset of large-scale silicate differentiation must have occurred later than 20±5 Ma after Solar System formation. The onset of silicate differentiation on Mars inferred here is significantly later than time estimates for segregation of the martian core which conservatively occurred within <10 Ma after Solar System formation. Thus, the new Mn-Cr data imply that there was a small, but resolvable, time gap of at least 5 Ma between core formation and magma ocean solidification on Mars. If the age of core segregation is taken at face value, our results imply that the martian magma ocean remained mostly molten over several Ma. This inferred longevity of the magma ocean is inconsistent with thermal models predicting rapid (<1 Ma) solidification of the martian magma ocean. Although there is currently no unique solution to this conundrum, our results can potentially be explained by a protracted history of impact bombardment that delayed differentiation in a shallow magma ocean on Mars, or perhaps more readily, by the presence of an early and dense atmosphere that acted as an insulator and prevented the magma ocean from cooling quickly.

58 GEOSCIENCES↗

Chemical and genetic characterization of the ungrouped pallasite Lieksa

The meteorite Lieksa was found in 2017 in Löpönvaara, Finland, and later donated to the Finnish Museum of Natural History. Here, we report siderophile element concentrations, genetic isotopic data, and a metal–silicate segregation age for the meteorite. The ~280 g Lieksa is ~80% metal and ~20% silicate and oxide inclusions by volume, with the inclusions consisting primarily of Fe-rich olivine. Due to Lieksa's silicate content, coupled with a texture characterized by metal enclosing the silicates, it has been classified as a pallasite. Lieksa's olivine and bulk chemical characteristics are distinct from those of the known pallasite and iron meteorite groups, consistent with its classification as ungrouped. The meteorite exhibits a flat, chondrite-normalized highly siderophile element pattern, consistent with an origin as an early crystallization product from a metallic melt with chondritic relative abundances. Molybdenum, Ru, and 183 W isotopic data indicate that Lieksa formed in the non-carbonaceous (NC) domain of the solar nebula. Radiogenic 182 W abundances for Lieksa yield a model metal–silicate segregation age of 1.5 ± 0.8 Myr after calcium-aluminum-rich inclusion formation, which is within the range established for other NC-type pallasite and iron meteorite parent bodies.

58 GEOSCIENCES↗

Spectroscopic Investigation of the High-Pressure Behavior of Aliphatic Hydrocarbon: Implications for Planetary Processes

Octadecane (C 18 H 38 ) is an aliphatic hydrocarbon that is abundant in carbonaceous chondritic meteorites. It is debated whether these hydrocarbons found in the meteorite are pristine or are a result of subsequent modifications as these meteorites are delivered to the Earth. It is well-known that meteorites are often subjected to extreme pressures and temperatures upon entering the Earth’s atmosphere. To explore the behavior of octadecane at high pressures, that is, how its molecular structure responds to compression, we use a diamond anvil cell in conjunction with Raman spectroscopy. Here, we find that at room temperatures, upon compression to ~5 GPa, a linear-chain octadecane molecule transforms into a bent-chain configuration. Similar transitions from linear to a bent configuration in other hydrocarbons have been documented. We find a linear correlation between the transition pressure from linear to bent configuration, and the chain length of the alkane, that is, longer chain lengths, is likely to be less stable in the linear configuration under compression. These kinks in the bent-chain configuration are likely sites for the dissociation of the longer chain hydrocarbons to smaller hydrocarbons. The octadecane sample examined in this study did not undergo any additional transition to the highest pressure (~18 GPa) explored in this study.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Size Ranges of Magnetic Domain States in Tetrataenite

Paleomagnetic studies of meteorites provide unique constraints on the evolution of magnetic fields in the early solar system. These studies rely on the identification of magnetic minerals that can retain stable magnetizations over ≳4.5 billion years (Ga). The ferromagnetic mineral tetrataenite (γ''-Fe 0.5 Ni 0.5 ) is found in iron, stony-iron and chondrite meteorite groups. Nanoscale intergrowths of tetrataenite have been shown to carry records of paleomagnetic fields, although the effect of magnetostatic interactions on their magnetic remanence acquisition remains to be fully understood. Tetrataenite can also occur as isolated, non-interacting, nanoscale grains in many meteorite groups, although the paleomagnetic potential of these grains is particularly poorly understood. Here, we aim to improve our understanding of tetrataenite magnetization to refine our knowledge of existing paleomagnetic analyses and broaden the spectrum of meteorite groups that can be used for future paleomagnetic studies. We present the results of analytical calculations and micromagnetic modeling of isolated tetrataenite grains with various geometries. We find that tetrataenite forms a stable single domain state at grain lengths between 6 and ~160 nm dependent on its elongation. It also possesses a magnetization resistant to viscous remagnetization over the lifetime of the solar system at 293 K. At larger grain sizes, tetrataenite's lowest energy state is a lamellar two-domain state, stable at Ga-scale timescales. Unlike many other magnetic minerals, tetrataenite does not form a single-vortex domain state due to its large uniaxial anisotropy. Our results show that single domain and two-domain tetrataenite grains carry an extremely stable magnetization and therefore are promising for paleomagnetic studies.

58 GEOSCIENCES↗

Oxygen isotope evidence from Ryugu samples for early water delivery to Earth by CI chondrites

The delivery of water to the inner Solar System, including Earth, is still a debated topic. A preferential role for hydrated asteroids in this process is supported by isotopic measurements. Carbonaceous chondrite (CC) meteorites represent our main source of information about these volatile-rich asteroids. However, the destruction of weaker materials during atmospheric entry creates a bias in our CC data. The return of surface materials from the C-type asteroid 162173 Ryugu by the Hayabusa2 spacecraft provides a unique opportunity to study high-porosity, low-density, primitive materials, unrepresented in the meteorite record. We measured the bulk oxygen isotope composition from four Ryugu particles and show that they most closely resemble the rare CI (CC Ivuna-type) chondrites, but with some differences that we attribute to the terrestrial contamination of the CI meteorites. We suggest that CI-related material is widespread among carbonaceous asteroids and a more important source of Earth’s water and other volatiles than its limited presence in our meteoritic collection indicates.

58 GEOSCIENCES↗

Accelerating Nature: Induced Atomic Order in Equiatomic FeNi

Abstract The production of locally atomically ordered FeNi (known by its meteoric mineral name, tetrataenite) is confirmed in bulk samples by simultaneous conversion X‐ray and backscattered γ‐ray 57 Fe Mössbauer spectroscopy. Up to 22 volume percent of the tetragonal tetrataenite phase is quantified in samples thermally treated under simultaneous magnetic‐ and stress‐field conditions for a period of 6 weeks, with the remainder identified as the cubic FeNi alloy. In contrast, all precursor samples consist only of the cubic FeNi alloy. Data from the processed alloys are validated using Mössbauer parameters derived from natural meteoritic tetrataenite. The meteoritic tetrataenite exhibits a substantially higher degree of atomic order than do the processed samples, consistent with their low uniaxial magnetocrystalline anisotropy energy of ≈1 kJ·m −3 . These results suggest that targeted refinements to the processing conditions of FeNi will foster greater atomic order and increased magnetocrystalline anisotropy, leading to an enhanced magnetic energy product. These outcomes also suggest that deductions concerning paleomagnetic conditions of the solar system, as derived from meteoritic data, may warrant re‐examination and re‐evaluation. Additionally, this work strengthens the argument that tetrataenite may indeed become a member of the advanced permanent magnet portfolio, helping to meet rapidly escalating green energy imperatives.

36 MATERIALS SCIENCE↗

Initial Conditions of Planet Formation: Time Constraints from Small Bodies and the Lifetime of Reservoirs in the Solar Protoplanetary Disk

This review explores the timescales of the initial phase of planet formation, from nebular dust (CAIs and chondrules) to planetesimal accretion and differentiation, using evidence from meteorite research. Aluminium-Mg systematics of CAIs indicate either an extended period of CAI formation (∼0.3 Ma) or an initial 26 Al heterogeneity, with evidence supporting a homogeneous 26 Al abundance in the protoplanetary disk. Thermal and aqueous alteration on the parent body can disturb the U-Pb and Al-Mg chronometers in chondrules. Focusing on relatively robust isochron data from plagioclase of pristine (types ≤3.05) chondrites indicates a shift in chondrule formation locations, moving from the inner to the outer disk over time. Ages of basaltic achondrites show that silicate differentiation on small bodies was well underway within the first few million years (Ma) of our solar system. Their age record, however, reveals inconsistencies between different chronometers, partly caused by (i) secondary disturbances due to thermal metamorphism, aqueous alteration, or impacts, (ii) the presence of xenolithic minerals, and (iii) potentially variable initial 26 Al abundances due to disturbances at the mineral scale. Nucleosynthetic isotope data indicate that parent bodies of iron and stony meteorites formed in two distinct regions within the protoplanetary disk: the inner, non-carbonaceous (NC) and the outer, carbonaceous (CC) region. Based on Hf-W chronometry it has been demonstrated that NC and CC parent bodies of magmatic iron meteorites segregated their cores within ∼1–3 Ma after CAI formation, implying that parent body accretion occurred within <1 Ma in both reservoirs. Combining accretion ages with nucleosynthetic data further reveals that, at first order, NC and CC reservoirs in the solar protoplanetary disk were established within 1 Ma and existed over several Ma with limited exchange between them. In the CR chondrite accretion region of the disk, planetary bodies formed over at least 3 Ma, while in most other regions, formation spanned at least 1 Ma, with minimal changes in nucleosynthetic isotope compositions. Aerodynamical size sorting of dust likely introduced or amplified some of these variations.

26Al distribution↗

Position-specific carbon isotopes of Murchison amino acids elucidate extraterrestrial abiotic organic synthesis networks

The Murchison meteorite is a well-studied carbonaceous chondrite with relatively high concentrations of amino acids thought to be endogenous to the meteorite, in part because they are characterized by carbon isotope (δ 13 C) values higher than those typical of terrestrial amino acids. Past studies have proposed that extraterrestrial amino acids in the Murchison meteorite could have formed by Strecker synthesis (for α-amino acids), Michael addition (for β-amino acids), or reductive amination, but a lack of constraints have prevented confident discrimination among these possibilities, or assignment of specific formation pathways to each of several specific amino acids. Position-specific carbon isotope analysis differentiates amongst these mechanisms by relating molecular sites to isotopically distinct carbon sources and by constraining isotope effects associated with elementary chemical reactions. Prior measurements of the position-specific carbon isotopic composition of α-alanine from the Murchison CM chondrite demonstrated that alanine’s high δ 13 C VPDB value is attributable to the amine carbon (δ 13 C VPDB = +142 ± 20‰), consistent with Strecker synthesis drawing on 13 C-rich carbonyl groups in precursors (Chimiak et al., 2021). Here, we measured the δ 13 C composition of fragment ions generated by electron impact ionization of derivatized α-alanine, β-alanine, and aspartic acid from Murchison via gas chromatography-Fourier transform mass spectrometry. α-Alanine’s amine carbon yielded δ 13 C VPDB = +109 ± 21‰, which is consistent with the previously measured value and with formation from 13 C-rich precursors. β-Alanine’s amine carbon presents a lower δ 13 C VPDB = +33 ± 24‰, which supports formation from 13 C-rich precursors but potentially via a Michael addition mechanism rather than Strecker synthesis. Aspartic acid’s amine carbon has δ 13 C VPDB = -14 ± 5‰, suggesting synthesis from precursors distinct from those that generated the alanine isomers. Further, these measurements indicate that Murchison amino acids are a mixture of compounds made from different synthesis mechanisms, though some subsets likely drew on the same substrates; this conclusion highlights the complexity of extraterrestrial organic synthesis networks and the potential of emerging methods of isotope ratio analysis to elucidate the details of those networks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

A Long-Lived Planetesimal Dynamo Powered by Core Crystallization

The existence of numerous iron meteorite groups indicates that some planetesimals underwent melting that led to metal-silicate segregation, sometimes producing metallic cores. Meteorite paleomagnetic records suggest that crystallization of these cores generated dynamo magnetic fields. In this work, we describe the magnetic history of the partially differentiated IIE iron meteorite parent body. This is the first planetesimal for which we have a time-resolved paleomagnetic record constrained by 40 Ar/ 39 Ar chronometry spanning several tens of million years (Ma). We find that the core of the IIE parent body generated a dynamo, likely powered by core crystallization, starting before 78 ± 13 Ma after solar system formation and lasting at least 80 Ma. Such extended core crystallization suggests that the core composed a substantial fraction of the body (≳ 13%–19% core-to-body radius ratio depending on the body’s radius), indicating efficient core formation within some partially differentiated planetesimals.

58 GEOSCIENCES↗

Isotopic signatures as tools to reconstruct the primordial architecture of the Solar System

The significant reorganization of the early Solar System due to giant planet migration has hampered our understanding of where planetary bodies formed. Previously employed proxies for reconstructing the primordial planetary architecture, such as water content or oxidation state, are complicated by post-accretionary processes. Furthermore we investigate basaltic achondrites for their nucleosynthetic isotope signatures in the elements neodymium (Nd) and zirconium (Zr) and show that they are—similar to previously investigated chondritic meteorites—characterized by a relative deficit in isotopes produced by the s-process of nucleosynthesis. Importantly, these data are well correlated with nucleosynthetic signatures observed in other elements, demonstrating that s-process matter was heterogeneously distributed throughout the early Solar System. By comparing these isotopic signatures with potential proxies for Solar System reconstruction and computer modeling, we here argue that this isotopic heterogeneity in bulk meteoritic materials is linked to the original heliocentric distance of formation. Such scaling of nucleosynthetic signatures with heliocentric distance could permit reconstruction of the primordial architecture of the Solar System by ‘cosmolocating’ the accretion orbits of meteoritic parent bodies as a function of incorporated s-process matter.

58 GEOSCIENCES↗

Petrogenesis, alteration, and shock history of intermediate shergottite Northwest Africa 7042: Evidence for hydrous magmatism on Mars?

We report Northwest Africa (NWA) 7042 is an intermediate, permafic shergottite consisting of two generations of zoned olivine (early olivine Fo 41-76 , and late-stage olivine Fo 46-56 ), complexly zoned pyroxene (En 35-64 Fs 22-46 Wo 5-34 ), maskelynitized feldspar and shock melt (An 5-30 Ab 16-61 Or 1-47 ), and accessory merrillite, apatite, ilmenite, titanomagnetite, Fe-Cr-Ti spinels, pyrrhotite, and baddeleyite. The olivine grains have been pervasively altered resulting in orange-brown stained cores with dark-brown margins, surrounded by significantly less altered overgrowth rims. This textural relationship suggests that the alteration of the cores took place at magmatic temperatures prior to crystallization of the rims on Mars. While this type of olivine alteration is rare in shergottites, it is similar to deuterically altered olivine in basalts and gabbros on Earth, caused by residual water-rich magmatic fluids. Launch-generated shock veins in NWA 7042 crosscut and displace several of the altered olivine grains indicating that the alteration occurred before ejection of the meteorite from Mars. However, NWA 7042 has also been subjected to extensive terrestrial weathering, with terrestrial calcite/barite veins occurring throughout the sample. Transmission electron microscopy analysis of the olivine alteration also reveals an absence of high-temperature phases typically associated with hydrous deuteric alteration on Earth, complicating our interpretation. The potential presence of deuterically altered olivine in NWA 7042 has significant implications, as it is the third martian meteorite where deuteric alteration of olivine has been observed (the others being NWA 10416, ALH 77005). The different mantle sources for the parental melts of these three meteorites would suggest many, if not all martian mantle reservoirs have the potential to produce water-rich magmas.

58 GEOSCIENCES↗