Carbonaceous Chondrite Meteorites Research Articles

The formation of H[formula omitted]O and Si-OH by H[formula omitted] irradiation in major minerals of carbonaceous chondrites

As the parent bodies of carbonaceous chondrite (CC) meteorites contain valuable information that will help us better understand the formation and evolution of the early solar system, it is vital to search for them. To date, searching for those parent bodies has been conducted by comparing visible to near-infrared reflectance spectra of CCs with those of small bodies. It is known that the reflectance spectra of small bodies and, more widely, airless planetary bodies can be modified via space weathering. However, the effects of irradiated solar wind protons, which account for 95 % of the solar wind, on the spectra of CC-like materials, are still poorly understood. Here we report on the experimental spectral modification of hydrous silicate minerals due to hydrogen irradiation via simulating the implantation of solar wind protons onto parent bodies of CCs. The samples we used for our experiment were serpentine and saponite, which are two major mineral components of CCs. We irradiated the samples with 10 keV H2+ ions to achieve the estimated saturation level (1.3 to 1.7 × 1018 ions cm−2), and measured their reflectance spectra in the wavelength range from 1.5 to 5.0μm both before and after irradiation. For serpentine, the sample was irradiated step by step, and the reflectance spectra were measured after each irradiation step.After irradiation, we observed changes in the absorption features at 2.77μm and 2.85μm. These changes imply that H2O and Si-OH radicals, respectively, would have been formed by a reaction between the irradiated hydrogen and the hydrous silicate minerals. In this study, spectral modifications due to hydrogen irradiation near 0.7μm and 2.3μm were not observed. This indicates that hydrogen irradiation broke the Si-O-Si bonding within the tetrahedra in hydrous silicate mineral structures, but it did not break the metal–OH bonding of the octahedra. In contrast to previous studies, our results imply that solar wind irradiation should also form H2O on anhydrous silicate minerals. This suggests the possibility of H2O formation on the surfaces of planetary bodies located inside of the snow line. The saturation timescale of spectral modification based on our results is estimated to be from 102 to 103 yr at 1 AU. This timescale is much shorter than that of the micrometeorite bombardment (106 to 107 yr), and it is comparable to the exposure age of small bodies. Therefore, we expect that spectral modification for small body surfaces would be mostly saturated.

Signatures of the post-hydration heating of highly aqueously altered CM carbonaceous chondrites and implications for interpreting asteroid sample returns

The CM carbonaceous chondrites have all been aqueously altered, and some of them were subsequently heated in a parent body environment. Here we have sought to understand the impact of short duration heating on a highly aqueously altered CM through laboratory experiments on Allan Hills (ALH) 83100. Unheated ALH 83100 contains 83 volume per cent serpentine within the fine-grained matrix and altered chondrules. The matrix also hosts grains of calcite and dolomite, which are often intergrown with tochilinite, Fe(Ni) sulphides (pyrrhotite, pentlandite), magnetite and organic matter. Some of the magnetite formed by replacement of Fe(Ni) sulphides that were accreted from the nebula. Laboratory heating to 400 °C has caused partial dehydroxylation of serpentine and loss of isotopically light oxygen leading to an increase in bulk δ18O and fall in Δ17O. Tochilinite has decomposed to magnetite, whereas carbonates have remained unaltered. With regards to infrared spectroscopy (4000–400 cm−1; 2.5–25 µm), heating to 400 °C has resulted in decreased emissivity (increased reflectance), a sharper and more symmetric OH band at 3684 cm−1 (2.71 µm), a broadening of the SiO stretching band together with movement of its minimum to longer wavenumbers, and a decreasing depth of the MgOH band (625 cm−1; 16 µm). The SiO bending band is unmodified by mild heating. With heating to 800 °C the serpentine has fully dehydroxylated and recrystallized to ∼Fo60/70 olivine. Bulk δ18O has further increased and Δ17O decreased. Troilite and pyrrhotite have formed, and recrystallization of pentlandite has produced Fe,Ni metal. Calcite and dolomite were calcined at ∼700 °C and in their place is an un-named Ca-Fe oxysulphide. Heating changes the structural order of organic matter so that Raman spectroscopy of carbon in the 800 °C sample shows an increased (D1 + D4) proportional area parameter. The infrared spectrum of the 800 °C sample confirms the abundance of Fe-bearing olivine and is very similar to the spectrum of naturally heated stage IV CM Pecora Escarpment 02010. The temperature-related mineralogical, chemical, isotopic and spectroscopic signatures defined in ALH 83100 will help to track the post-hydration thermal histories of carbonaceous chondrite meteorites, and samples returned from the primitive asteroids Ryugu and Bennu.

Are quasicrystals really so rare in the Universe?

Abstract Until 2009, the only known quasicrystals were synthetic, formed in the laboratory under highly controlled conditions. Conceivably, the only quasicrystals in the Milky Way, perhaps even in the Universe, were the ones fabricated by humans, or so it seemed. Then came the report that a quasicrystal with icosahedral symmetry had been discovered inside a rock recovered from a remote stream in far eastern Russia, and later that the rock proved to be an extraterrestrial, a piece of a rare CV3 carbonaceous chondrite meteorite (known as Khatyrka) that formed 4.5 billion years ago in the pre-solar nebula. At present, the only known examples of natural quasicrystals are from the Khatyrka meteorite. Does that mean that quasicrystals must be extremely rare in the Universe? In this speculative essay, we present several reasons why the answer might be no. In fact, quasicrystals may prove to be among the most ubiquitous minerals found in the Universe.

A miniaturized XRF instrument for in situ planetary exploration: The Active X-Ray Spectrometer (AXRS)

The Active X-Ray Spectrometer (AXRS) was developed at Johns Hopkins Applied Physics Lab (APL) to be utilized in landed planetary exploration spacecraft seeking to better understand bulk rock geochemistry of lithophile materials. The AXRS sensor head has a mass of 360 ​g, fits within an envelope of 11 ​× ​6 ​× ​5 ​cm3, and consumes <5 ​W during operation. AXRS has an average relative uncertainty of 9% for deriving the abundances of major and minor elements, and measurement precision ≤10% for all elements. Measurements were made with powdered samples, analogous to high-processed regoliths as expected on the surfaces of airless planetary objects. These specifications are equal to or better than those published for other x-ray instruments used in landed planetary exploration missions. We explored several mission applications for AXRS via analysis of planetary materials under mission conditions. These include the ability to: 1) resolve sub-type of carbonaceous chondrite meteorite via measured abundances of various lithophile element ratios based on volatility, 2) identify low-Fe lunar anorthosite, from high-Fe lunar anorthosite, from lunar mare using bulk Ca, Al, Fe, Mg, and 3) resolve various Venus- and Mars-like volcanic rocks utilizing bulk Si, K, and Na.

Influence of Gamma Ray Irradiation on the Optical Properties of Calcite and Dolomite

The class of carbonaceous chondrite meteorites has carbon in their structures, similarly to the terrestrial calcite and dolomite rocks, and contains the group =CO3 linked to Ca and/or Mg, which may be, in principle, more susceptible to the action of the spatial gamma radiation (γ-R) due to the presence of these light-atom elements. On the present work, we used a variety of optical techniques to investigate the possible effects of γ-R produced by an artificial 192Ir source in terrestrial calcite and dolomite, which may allow to understand the effect of the spatial radiation in that celestial bodies of the solar system. As a result, we verified that the γ-R irradiation caused the effect of untrapping of electrons from deep color centers, that spatially migrate to other color centers on the samples, resulting on the change of the electron energetic configuration.

Direct Force Measurement of Pulsed Laser Ablation of Asteroid Simulants

Subnanosecond laser ablation of asteroid simulants has been studied, and direct force measurements were made. A 0.7 ns pulsed laser was used, with a 40 kHz pulse repetition frequency, 1064 nm wavelength, and 33 W average power. High-fidelity simulants for carbonaceous chondrite meteorites of types CM, CR, and CI, as well as pyroxene rock and 6061 aluminum were ablated. The force response over 500 ms of ablation was measured using a load cell. In addition, the samples were weighed before and after ablation to determine the mass removal rate. Based on these measurements, the momentum coupling coefficient, specific impulse, and ablation efficiency were calculated. The asteroid analog materials were found to have a modestly higher momentum coupling coefficient than aluminum, although the specific impulse and efficiency were much lower. For asteroid mitigation missions, the asteroid itself is used as the propellant, and so a low specific impulse poses no problem.

Hypervelocity cratering and disruption of the Northwest Africa 4502 carbonaceous chondrite meteorite: Implications for crater production, catastrophic disruption, momentum transfer and dust production on asteroids

The meteorites provide samples of their asteroidal parent bodies, allowing laboratory measurements of the response of asteroidal material to hypervelocity impacts. The meteorites span a wide range of physical properties, with porosities ranging from near zero to more than 40%, comparable to the range determined for stony asteroids. To investigate the effects of target properties on cratering, impact disruption, momentum transfer and dust production we have begun a series of hypervelocity impact experiments on various types of meteorite targets. In this work whole stones or fragments of the Northwest Africa 4502 (NWA 4502) CV3 carbonaceous chondrite were impacted by 1/16” or 1/8” Al-spheres at speeds ranging from 4.11 to 5.89 ​km/s at the NASA Ames Vertical Gun Range. These samples had a mean porosity of ~2.1% and a mean unconfined compressive strength of ~32.9 ​MPa. Eight hypervelocity disruptions demonstrated that these NWA 4502 targets are less resistant to disruption, i.e., they require less impactor kinetic energy per unit target mass to produce an equivalent disruption, than non-porous terrestrial basalt targets or ordinary chondrite meteorite targets. The threshold collisional specific energy, Q∗D, for these NWA 4502 targets is ~224 ​J/kg, which is significantly lower than the ~1795 ​J/kg value we measured previously for the moderately porous (~6.4%) ordinary chondrite meteorite Northwest Africa 869. This likely results from the numerous cracks crosscutting the NWA 4502 samples. We measured the post-impact momentum of seven NWA 4502 cratering events and found a mean momentum transfer of 3.55 times the momentum of the projectile, showing that the recoil from the crater ejecta significantly exceeded the direct momentum transferred by absorption of the projectile. In two cases we found much higher momentum transfer values (11.72 and 8.95), suggesting these two impactors struck a different material, likely hydrous weathering veins, which fill the cracks, than the other five NWA 4502 cratering impacts. This suggests that hydrous asteroids and comets would experience significantly more recoil from hypervelocity impact than anhydrous targets having similar strength and porosity.

Mineralogical and Chemical Investigations of the Amguid Crater (Algeria): Is there Evidence on an Impact Origin?

Mineralogical and chemical investigations were carried out on intra-craterial bedrocks (Lower Devonian sandstone) and regolithic residual soil deposits present around the Amguid structure, to discuss the hypothesis of its formation through a relatively recent (about 0.1 Ma) impact event. Observations with an optical microscope on intra-craterial rocks do not unequivocally confirm the presence of impact correlated microscopic planar deformation features (PDFs) in quartz crystals. Field observations, and optical and instrumental analysis (Raman spectroscopy) on rocks and soils (including different granulometric fractions) do not provide any incontrovertible pieces of evidence of high energy impact effects or products of impact (e.g., high pressure—temperature phases, partially or totally melted materials, etc.) either in target rocks or in soils. A series of selected main and trace elements (Al, Fe, Mg, Ni, Co and Cu) were analysed on rocks and soils to evaluate the presence in these materials of extraterrestrial sources. Comparative chemical data on rocks and soils suggest that these last are significantly enriched in Fe-poor Mg-rich materials, and in Co, Ni and Cu, in the order. A large number of EDAX-SEM analyses on separated soil magnetic particles indicate an abnormally high presence of Al-free Mg-rich sub-spherical or drop-like silicate particles, showing very similar bulk chemistries compatible with forsterite olivine. Some particles were found associated with a Ni-rich iron metal phase, and this association suggests a specific extraterrestrial origin for them. Electron microscope analysis made on a large number of soil magnetic particles indicates that 98% of them are terrestrial phases (almandine garnet, tourmaline and Fe-oxides, in abundance order), whereas, only a few grains are of questionable origin. One of the Mg-rich silicate particles was found to be a forsterite (Mg = 0.86) Mn-rich (MnO: 0.23%) Cr-free olivine, almost surely of extraterrestrial sources. Electron microprobe analysis of three soil particles allowed identification of uncommon Cr-rich (Cr2O3 about 8%) spinels, poorly compatible with an origin from terrestrial sources, and in particular from local source rocks. We propose a specific extraterrestrial origin for sub-spherical olivine particles characterised by quite similar magnesian character. Excluding any derivation of these particles from interplanetary dust, two other possible extraterrestrial sources should be considered for them, i.e., either normal micrometeorite fluxes or strongly un-equilibrated, or the Vigarano type Carbonaceous (CV) chondrite meteorite material. In this case, further studies will confirm an impact origin for Amguid, as such magnesian olivine components found in soils might represent the only remnants of a vaporised projectile of ordinary non-equilibrated meteoritic composition.

Momentum transfer in hypervelocity cratering of meteorites and meteorite analogs: Implications for orbital evolution and kinetic impact deflection of asteroids

Kinetic impact is regarded as an effective way to divert an asteroid on a collision course with the Earth. However, asteroids show a wide diversity in their mineralogy, porosity, and water content. Asteroids range in composition from primitive undifferentiated objects to differentiated objects. Among the undifferentiated asteroids they range from more reflective, carbon-poor bodies to darker, carbonaceous bodies. Porosities of asteroids range from 0 to >50%, with most >20%, and some asteroids exhibit a 0.7 µm water feature in their reflection spectra. Mineralogy, porosity and hydration are each expected to influence the momentum transferred in hypervelocity collisions. We conducted a series of measurements of the post-impact momentum, which is characterized by a factor β, the ratio of the total linear momentum acquired by the target to the momentum of the impactor. We measured β for anhydrous meteorites, which sample their asteroidal parent bodies, spanning a wide range of porosities: including 7 samples of the CV3 carbonaceous chondrite Northwest Africa (NWA) 4502 (2.1% porosity), 7 samples of the ordinary chondrite NWA 869 (6.4% porosity), 4 samples of the ordinary chondrite Saratov (15.6% porosity), and, to extend our measurements to higher porosity than is found among meteorites, 2 samples of terrestrial pumice (80% porosity). We also measured β for hydrous meteorite analog targets: including 2 samples of terrestrial serpentine (17.9% porosity) and 4 samples of terrestrial montmorillonite (51.5% porosity), the two clay minerals that dominate the composition of the hydrous CI carbonaceous chondrite meteorites, as well as 4 samples of hydrous meteorite analog material prepared by powdering and hydrating an anhydrous carbonaceous chondrite. We found that for both the anhydrous and the hydrous samples β decreased with increasing porosity, consistent with hydrocode modeling. However, the β values we measured for the ∼5 km/s impacts onto these anhydrous samples, with β = 3.55 for NWA 4502, 2.69 for NWA 869, 2.10 for Saratov, and 2.15 for pumice, are larger than results from hydrocode modeling for 10 km/s impacts into relatively strong, porous rock targets. The β values for the moderate porosity (17.9%) hydrous serpentine targets (β = 4.70), the highly porous (51.55%) hydrous montmorillonite targets (β = 2.79), and the moderately porous CI-analog targets (β = 2.99) are each significantly larger than the β value for anhydrous targets of comparable porosities. This is likely due to jetting of water vapor, which could significantly affect the deflection of hydrous asteroids and icy comets in natural or human-induced collisions.

Enceladus: First Observed Primordial Soup Could Arbitrate Origin-of-Life Debate.

A recent breakthrough publication has reported complex organic molecules in the plumes emanating from the subglacial water ocean of Saturn's moon Enceladus (Postberg et al., 2018, Nature 558:564–568). Based on detailed chemical scrutiny, the authors invoke primordial or endogenously synthesized carbon-rich monomers (<200 u) and polymers (up to 8000 u). This appears to represent the first reported extraterrestrial organics-rich water body, a conceivable milieu for early steps in life's origin (“prebiotic soup”). One may ask which origin-of-life scenario appears more consistent with the reported molecular configurations on Enceladus. The observed monomeric organics are carbon-rich unsaturated molecules, vastly different from present-day metabolites, amino acids, and nucleotide bases, but quite chemically akin to simple lipids. The organic polymers are proposed to resemble terrestrial insoluble kerogens and humic substances, as well as refractory organic macromolecules found in carbonaceous chondritic meteorites. The authors posit that such polymers, upon long-term hydrous interactions, might break down to micelle-forming amphiphiles. In support of this, published detailed analyses of the Murchison chondrite are dominated by an immense diversity of likely amphiphilic monomers. Our specific quantitative model for compositionally reproducing lipid micelles is amphiphile-based and benefits from a pronounced organic diversity. It thus contrasts with other origin models, which require the presence of very specific building blocks and are expected to be hindered by excess of irrelevant compounds. Thus, the Enceladus finds support the possibility of a pre-RNA Lipid World scenario for life's origin.

Landing on the surface of Ryugu

Asteroids In October 2018, the Hayabusa2 spacecraft dropped the Mobile Asteroid Surface Scout (MASCOT) lander onto the surface of the asteroid (162173) Ryugu. Jaumann et al. analyzed images taken by the MASCOT camera during its descent and when resting on the surface. Colored light-emitting diodes were used to illuminate the lander's surroundings at night and produce color images. Ryugu's surface is dominated by two types of rock, but there is no evidence for fine-grained dust. Millimeter-sized inclusions in the rocks are similar to those present in carbonaceous chondrite meteorites. MASCOT operated for 17 hours on the surface before its nonrechargeable batteries ran out. Science , this issue p. [817][1] [1]: /lookup/doi/10.1126/science.aaw8627

Images from the surface of asteroid Ryugu show rocks similar to carbonaceous chondrite meteorites.

The near-Earth asteroid (162173) Ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu's surface on 3 October 2018. We present images from the MASCOT camera (MASCam) taken during the descent and while on the surface. The surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. Rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. Close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. The inclusions appear similar to those in carbonaceous chondrite meteorites.

The Yamato-type (CY) carbonaceous chondrite group: Analogues for the surface of asteroid Ryugu?

We report new mineralogical, petrographic and noble gas analyses of the carbonaceous chondrite meteorites Y-82162 (C1/2ung), Y-980115 (CI1), Y-86029 (CI1), Y-86720 (C2ung), Y-86789 (C2ung), and B-7904 (C2ung). Combining our results with literature data we show that these meteorites experienced varying degrees of aqueous alteration followed by short-lived thermal metamorphism at temperatures of >500 °C. These meteorites have similar mineralogy, textures and chemical characteristics suggesting that they are genetically related, and we strongly support the conclusion of Ikeda (1992) that they form a distinct group, the CYs (“Yamato-type”). The CY chondrites have the heaviest oxygen isotopic compositions (δ17O ˜12‰, δ18O ˜22‰) of any meteorite group, high abundances of Fe-sulphides (˜10 ‒ 30 vol%) and phosphates, and contain large grains of periclase and unusual objects of secondary minerals not reported in other carbonaceous chondrites. These features cannot be attributed to parent body processes alone, and indicate that the CYs had a different starting mineralogy and/or alteration history to other chondrite groups, perhaps because they formed in a different region of the protoplanetary disk. The short cosmic-ray exposure ages (≤1.3 Ma) of the CY chondrites suggest that they are derived from a near-Earth source, with recent observations by the Hayabusa2 spacecraft highlighting a possible link to the rubble-pile asteroid Ryugu.

Sulfur isotope study of sulfides in CI, CM, C2ung chondrites and volatile-rich clasts – Evidence for different generations and reservoirs of sulfide formation

Abstract Deciphering aspects of the solar system’s formation process and the origin of planetary bodies can be achieved by examining primitive solar system materials, as these materials reflect the early solar system composition and may represent the building blocks of planetary bodies. Along these lines, knowing the original composition of carbonaceous chondrite meteorites is a valuable asset for determining the conditions in the parent bodies where they formed. Therefore, to determine the key characteristics of the parent bodies from which the carbonaceous chondrites and primitive materials are derived, we examined chemical and sulfur isotope compositions of sulfides in CM, CI and C2ung carbonaceous chondrites as well as from CM- and CI-like volatile-rich clasts; such an investigation allows us to explore the origin of these sulfides and to determine the primordial S composition of their parent body source region. In this study, sulfides from 7 CM, CI, and C2ung carbonaceous chondrites and 16 chondritic and achondritic breccias containing volatile-rich clasts were analyzed by electron microprobe and SIMS. Different sulfides were found, which shows evidence of different formation origins. Based on compositions and exsolution textures, we suggest that one fraction of the sulfides in both clasts and chondrites formed at high temperatures prior to incorporation into the parent body. The other sulfides most likely have a secondary origin and precipitated during fluid–rock interaction. Furthermore, differences in the S isotopic signature of the sulfides in chondrites correlate with the degree of aqueous alteration of the carbonaceous host rocks (CM or CI). Studying the sulfides of the volatile-rich clasts in brecciated chondrites and achondrites, a similar fractionation cannot be seen. Even though the mineralogy of CI chondrites and CI-like clasts is similar, the sulfides in CI chondrites appear to be enriched in heavy isotopes compared to those in the clasts (δ34S + 1‰ (CI) vs −2‰ (CI-like clast). This could have been caused by different alteration conditions, or it represents a different sampling reservoir. In this study a large S isotopic fractionation between pentlandite and pyrrhotite was found in large primarily formed sulfides showing exsolution textures, indicating that pentlandite prefers to incorporate light S isotopes. Considering the S isotope composition of the exsolved phase which can be found in CM- and CI-like clasts, the pristine δ34S value of the original monosulfide solid solution (mss) is estimated to be ∼−2‰. This value possibly resembles the sampling reservoir from which the sulfides formed, indicating that both CM- and CI-like clasts derived from a similar reservoir, and this reservoir is different from the formation reservoir of the CI chondrites.

Simulated asteroid materials based on carbonaceous chondrite mineralogies

AbstractA set of high‐fidelity simulated asteroid materials, or simulants, was developed based on the mineralogy of carbonaceous chondrite meteorites. Three varieties of simulant were developed based on CI1 chondrites (typified by Orgueil), CM2 chondrites (typified by Murchison), and CR2/3 chondrites (multiple samples). The simulants were designed to replicate the mineralogy and physical properties of the corresponding meteorites and anticipated asteroid surface materials as closely as is reasonably possible for bulk amounts. The simulants can be made in different physical forms ranging from larger cobbles to fine‐grained regolith. We analyzed simulant prototypes using scanning electron microscopy, X‐ray fluorescence, reflectance spectroscopy at ambient conditions and in vacuum, thermal emission spectroscopy in a simulated asteroid environment chamber, and combined thermogravimetry and evolved gas analysis. Most measured properties compare favorably to the reference meteorites and therefore to predicted volatile‐rich asteroid surface materials, including boulders, cobbles, and fine‐grained soils. However, there were also discrepancies, and mistakes were made in the original mineral formulations that will be updated in the future. The asteroid simulants are available to the community from the nonprofit Exolith Lab at UCF, and the mineral recipes are freely published for other groups to reproduce and modify as they see fit.

Survival of Extremotolerant Bacteria from the Mukundpura Meteorite Impact Crater.

Carbonaceous meteorites provide clues with regard to prebiotic chemistry and the origin of life. Geological Survey of India recorded a carbonaceous chondrite meteorite fall in Mukundpura, India, on June 6, 2017. We conducted a study to investigate the microbial community that survived the meteorite impact. 16S rRNA metagenomic sequencing indicates the presence of Actinobacteria, Proteobacteria, and Acidobacteria in meteorite impact soil. Comparative phylogenetic analysis revealed an intriguing abundance of class Bacilli in the impact soil. Bacillus thermocopriae IR-1, a moderately thermotolerant organism, was isolated from a rock, impacted by the Mukundpura meteorite. We investigated the resilience of B. thermocopriae IR-1 to environmental stresses and impact shock in a Reddy shock tube. Bacillus thermocopriae IR-1 survived (28.82% survival) the effect of shock waves at a peak shock pressure of 300 kPa, temperature 400 K, and Mach number of 1.47. This investigation presents the first report on the effect of impact shock on B. thermocopriae IR-1. The study is also the first report on studying the microbial diversity and isolation of bacteria from impact crater soil immediately after meteorite impact event.

Carbonaceous chondrite meteorites as a record of protoplanetary disk conditions

AbstractChondritic meteorites, and especially the most volatile-rich chondrites, the carbonaceous chondrites, preserve a record of the solar protoplanetary disk dust component and how it has been changed both in the disk environment itself and in its asteroidal parent body. Here we review some of the key features of carbonaceous chondrites and report some new data on their organics component. These show that the nebula reached temperature of &gt;10000C, but only very locally, to produce chondrules. Most meteoritic material underwent thermal and/or aqueous processing, but some retain delicate nebular components such as complex organic molecules and amorphous silicates.

The surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy.

The near-Earth asteroid 162173 Ryugu, the target of the Hayabusa2 sample-return mission, is thought to be a primitive carbonaceous object. We report reflectance spectra of Ryugu's surface acquired with the Near-Infrared Spectrometer (NIRS3) on Hayabusa2, to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micrometers was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, which is consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

The Maribo CM2 meteorite fall—Survival of weak material at high entry speed

AbstractHigh entry speed (&gt;25 km s−1) and low density (&lt;2500 kg m−3) are the two factors that lower the chance of a meteoroid to drop meteorites. The 26 g carbonaceous (CM2) meteorite Maribo recovered in Denmark in 2009 was delivered by a bright bolide observed by several instruments across northern and central Europe. By reanalyzing the available data, we confirmed the previously reported high entry speed of (28.3 ± 0.3) km s−1 and trajectory with slope of 31° to the horizontal. In order to understand how such a fragile material survived, we applied three different models of meteoroid atmospheric fragmentation to the detailed bolide light curve obtained by radiometers located in Czech Republic. The Maribo meteoroid was found to be quite inhomogeneous with different parts fragmenting at different dynamic pressures. While 30–40% of the (2000 ± 1000) kg entry mass was destroyed already at 0.02 MPa, another 25–40%, according to different models, survived without fragmentation up to the relatively large dynamic pressures of 3–5 MPa. These pressures are only slightly lower than the measured tensile strengths of hydrated carbonaceous chondrite (CC) meteorites and are comparable with usual atmospheric fragmentation pressures of ordinary chondritic (OC) meteoroids. While internal cracks weaken OC meteoroids in comparison with meteorites, this effect seems to be absent in CC, enabling meteorite delivery even at high speeds, though in the form of only small fragments.

Thermal alteration of labile elements in carbonaceous chondrites

Carbonaceous chondrite meteorites are some of the oldest Solar System planetary materials available for study. The CI group has bulk abundances of elements similar to those of the solar photosphere. Of particular interest in carbonaceous chondrite compositions are labile elements, which vaporize and mobilize efficiently during post-accretionary parent-body heating events. Thus, they can record low-temperature alteration events throughout asteroid evolution. However, the precise nature of labile-element mobilization in planetary materials is unknown. Here we characterize the thermally induced movements of the labile elements S, As, Se, Te, Cd, Sb, and Hg in carbonaceous chondrites by conducting experimental simulations of volatile-element mobilization during thermal metamorphism. This process results in appreciable loss of some elements at temperatures as low as 500 K. This work builds on previous laboratory heating experiments on primitive meteorites and shows the sensitivity of chondrite compositions to excursions in temperature. Elements such as S and Hg have the most active response to temperature across different meteorite groups. Labile element mobilization in primitive meteorites is essential for quantifying elemental fractionation that occurred on asteroids early in Solar System history. This work is relevant to maintaining a pristine sample from asteroid (101955) Bennu from the OSIRIS-REx mission and constraining the past orbital history of Bennu. Additionally, we discuss thermal effects on surface processes of near-Earth asteroids, including the thermal history of “rock comets” such as (3200) Phaethon. This work is also critical for constraining the concentrations of contaminants in vaporized water extracted from asteroid regolith as part of future in situ resource utilization for sustained robotic and human space exploration.