The Fe/S ratio of pyrrhotite group sulfides in chondrites: An indicator of oxidation and implications for return samples from asteroids Ryugu and Bennu

Determining compositional trends among individual minerals is key to understanding the thermodynamic conditions under which they formed and altered, and is also essential to maximizing the scientific value of small extraterrestrial samples, including returned samples and meteorites. Here we report the chemical compositions of Fe-sulfides, focusing on the pyrrhotite-group sulfides, which are ubiquitous in chondrites and are sensitive indicators of formation and alteration conditions in the protoplanetary disk and in small Solar System bodies. Our data show that while there are trends with the at.% Fe/S ratio of pyrrhotite with thermal and aqueous alteration in some meteorite groups, there is a universal trend between the Fe/S ratio and degree of oxidation. Relatively reducing conditions led to the formation of troilite during: (1) chondrule formation in the protoplanetary disk (i.e., pristine chondrites) and (2) parent body thermal alteration (i.e., LL4 to LL6, CR1, CM, and CY chondrites). Oxidizing and sulfidizing conditions led to the formation of Fe-depleted pyrrhotite with low Fe/S ratios during: (1) aqueous alteration (i.e., CM and CI chondrites), and (2) thermal alteration (i.e., CK and R chondrites). The presence of troilite in highly aqueously altered carbonaceous chondrites (e.g., CY, CR1, and some CM chondrites) indicates they were heated after aqueous alteration. The presence of troilite, Fe-depleted pyrrhotite, or pyrite in a chondrite can provide an estimate of the oxygen and sulfur fugacities at which it was formed or altered. The data reported here can be used to estimate the oxygen fugacity of formation and potentially the aqueous and/or thermal histories of sulfides in extraterrestrial samples, including those returned by the Hayabusa2 mission and due to be returned by the OSIRIS-REx mission in the near future.

The relationship between CM and CO chondrites: Insights from combined analyses of titanium, chromium, and oxygen isotopes in CM, CO, and ungrouped chondrites

A close relationship between CM and CO chondrites has been suggested by previous petrologic and isotopic studies, leading to the suggestion that they may originate from similar precursor materials or even a common parent body. In this study, we evaluate the genetic relationship between CM and CO chondrites using Ti, Cr, and O isotopes. We first provide additional constraints on the ranges of ε⁵⁰Ti and ε⁵⁴Cr values of bulk CM and CO chondrites by reporting the isotopic compositions of CM2 chondrites Murchison, Murray, and Aguas Zarcas and the CO3.8 chondrite Isna. We then report the ε⁵⁰Ti and ε⁵⁴Cr values for several ungrouped and anomalous carbonaceous chondrites that have been previously reported to exhibit similarities to the CM and/or CO chondrite groups, including Elephant Moraine (EET) 83226, EET 83355, Grosvenor Mountains (GRO) 95566, MacAlpine Hills (MAC) 87300, MAC 87301, MAC 88107, and Northwest Africa (NWA) 5958, and the O-isotope compositions of a subset of these samples. We additionally report the Ti, Cr, and O isotopic compositions of additional ungrouped chondrites LaPaz Ice Field (LAP) 04757, LAP 04773, Lewis Cliff (LEW) 85332, and Coolidge to assess their potential relationships with known carbonaceous and ordinary chondrite groups. LAP 04757 and LAP 04773 exhibit isotopic compositions indicating they are low-FeO ordinary chondrites. The isotopic compositions of Murchison, Murray, Aguas Zarcas, and Isna extend the compositional ranges defined by the CM and CO chondrites in ε⁵⁰Ti versus ε⁵⁴Cr space. The majority of the ungrouped carbonaceous chondrites with documented similarities to the CM and/or CO chondrites plot outside the CM and CO group fields in plots of ε⁵⁰Ti versus ε⁵⁴Cr, Δ¹⁷O versus ε⁵⁰Ti, and Δ¹⁷O versus ε⁵⁴Cr. Therefore, based on differences in their Ti, Cr, and O isotopic compositions, we conclude that the CM, CO, and ungrouped carbonaceous chondrites likely represent samples of multiple distinct parent bodies. We also infer that these parent bodies formed from precursor materials that shared similar isotopic compositions, which may indicate formation in regions of the protoplanetary disk that were in close proximity to each other.

Chromium isotopic insights into the origin of chondrite parent bodies and the early terrestrial volatile depletion

Chondrites are meteorites from undifferentiated parent bodies that provide fundamental information about early Solar System evolution and planet formation. The element Cr is highly suitable for deciphering both the timing of formation and the origin of planetary building blocks because it records both radiogenic contributions from ⁵³Mn-⁵³Cr decay and variable nucleosynthetic contributions from the stable ⁵⁴Cr nuclide. Here, we report high-precision measurements of the massindependent Cr isotope compositions (ε⁵³Cr and ε⁵⁴Cr) of chondrites (including all carbonaceous chondrites groups) and terrestrial samples using for the first time a multi-collection inductively-coupled-plasma mass-spectrometer to better understand the formation histories and genetic relationships between chondrite parent bodies. With our comprehensive dataset, the order of decreasing ε⁵⁴Cr (per ten thousand deviation of the ⁵⁴Cr/⁵²Cr ratio relative to a terrestrial standard) values amongst the carbonaceous chondrites is updated to CI = CH ≥ CB ≥ CR ≥ CM ≈ CV ≈ CO ≥ CK > EC > OC. Chondrites from CO, CV, CR, CM and CB groups show intra-group ε⁵⁴Cr heterogeneities that may result from sample heterogeneity and/or heterogeneous accretion of their parent bodies. Resolvable ε⁵⁴Cr (with 2SE uncertainty) differences between CV and CK chondrites rule out an origin from a common parent body or reservoir as has previously been suggested. The CM and CO chondrites share common ε⁵⁴Cr characteristics, which suggests their parent bodies may have accreted their components in similar proportions. The CB and CH chondrites have low-Mn/Cr ratios and similar ε⁵³Cr values to the CI chondrites, invalidating them as anchors for a bulk ⁵³Mn-⁵³Cr isochron for carbonaceous chondrites. Bulk Earth has a ε⁵³Cr value that is lower than the average of chondrites, including enstatite chondrites. This depletion may constrain the timing of volatile loss from the Earth or its precursors to be within the first million years of Solar System formation and is incompatible with Earth's accretion via any of the known chondrite groups as main contributors, including enstatite chondrites.

Advances in Cosmochemistry Enabled by Antarctic Meteorites

At present, meteorites collected in Antarctica dominate the total number of the world's known meteorites. We focus here on the scientific advances in cosmochemistry and planetary science that have been enabled by access to, and investigations of, these Antarctic meteorites. A meteorite recovered during one of the earliest field seasons of systematic searches, Elephant Moraine (EET) A79001, was identified as having originated on Mars based on the composition of gases released from shock melt pockets in this rock. Subsequently, the first lunar meteorite, Allan Hills (ALH) 81005, was also recovered from the Antarctic. Since then, many more meteorites belonging to these two classes of planetary meteorites, as well as other previously rare or unknown classes of meteorites (particularly primitive chondrites and achondrites), have been recovered from Antarctica. Studies of these samples are providing unique insights into the origin and evolution of the Solar System and planetary bodies.

Petrographic and compositional indicators of formation and alteration conditions from LL chondrite sulfides

Sulfide minerals occur in many types of extraterrestrial samples and are sensitive indicators of the conditions under which they formed or were subsequently altered. Here we report that chemical and petrographic analyses of Fe,Ni sulfides can be used to determine the metamorphic type of the host LL chondrite, and constrain their alteration conditions. Our data show that the major- and minor-element compositions of the pyrrhotite-group sulfides (dominantly troilite) and pentlandite vary with degree of thermal metamorphism experienced by their host chondrite. We find that Fe,Ni sulfides in LL3 chondrites formed during chondrule cooling prior to accretion, whereas those in LL4 to LL6 chondrites formed during cooling after thermal metamorphism in the parent body, in agreement with previous work. High degrees of shock (i.e., ≥S5) caused distinct textural, structural, and compositional changes that can be used to identify highly shocked samples. Distinct pyrrhotite-pentlandite textures and minerals present in Appley Bridge (LL6) suggest that they cooled more slowly and therefore occurred at greater depth(s) in the host parent body than those of the other metamorphosed LL chondrites studied here. Sulfides in all LL chondrites studied formed under similar sulfur fugacities, and the metamorphosed LL chondrites formed under similar oxygen fugacities. The data reported here can be applied to the study of other LL chondrites and to sulfides in samples of asteroid Itokawa returned by the Hayabusa mission in order to learn more about the formation and alteration history of the LL chondrite parent body.

The background temperature of the protoplanetary disk within the first four million years of the Solar System

The background temperature of the protoplanetary disk is a fundamental but poorly constrained parameter that strongly influences a wide range of conditions and processes in the early Solar System, including the widespread process(es) by which chondrules originate. Chondrules, mm-scale objects composed primarily of silicate minerals, were formed in the protoplanetary disk almost entirely during the first four million years of Solar System history but their formation mechanism(s) are poorly understood. Here we present new constraints on the sub-silicate solidus cooling rates of chondrules at <873 K (600°C) using the compositions of sulfide minerals. We show that chondrule cooling rates remained relatively rapid (~10⁰ to 10¹ K/hr) between 873 and 503 K, which implies a protoplanetary disk background temperature of <503 K (230°C) and is consistent with many models of chondrule formation by shocks in the solar nebula, potentially driven by the formation of Jupiter and/or planetary embryos, as the chondrule formation mechanism. This protoplanetary disk background temperature rules out current sheets and resulting short-circuit instabilities as the chondrule formation mechanism. More detailed modeling of chondrule cooling histories in impacts is required to fully evaluate impacts as a chondrule formation model. These results motivate further theoretical work to understand the expected thermal evolution of chondrules at ≤873 K under a variety of chondrule formation scenarios.

LOW-TEMPERATURE AQUEOUS ALTERATION ON THE CR CHONDRITE PARENT BODY: IMPLICATIONS FROM IN SITU OXYGEN-ISOTOPE ANALYSES

The presence of hydrated minerals in chondrites indicates that water played an important role in the geologic evolution of the early Solar System; however, the process of aqueous alteration is still poorly understood. Renazzo-like carbonaceous (CR) chondrites are particularly well-suited for the study of aqueous alteration. Samples range from being nearly anhydrous to fully altered, essentially representing snapshots of the alteration process through time. We studied oxygen isotopes in secondary-minerals from six CR chondrites of varying hydration states to determine how aqueous fluid conditions (including composition and temperature) evolved on the parent body. Secondary minerals analyzed included calcite, dolomite, and magnetite. The O-isotope composition of calcites ranged from δ¹⁸O ≈ 9 to 35 ‰, dolomites from δ¹⁸O ≈ 23 to 27 ‰, and magnetites from δ¹⁸O ≈ -18 to 5 ‰. Calcite in less-altered samples showed more evidence of fluid evolution compared to heavily altered samples, likely reflecting lower water/rock ratios. Most magnetite plotted on a single trend, with the exception of grains from the extensively hydrated chondrite MIL 090292. The MIL 090292 magnetite diverges from this trend, possibly indicating an anomalous origin for the meteorite. If magnetite and calcite formed in equilibrium, then the relative ¹⁸O fractionation between them can be used to extract the temperature of co-precipitation. Isotopic fractionation in Al Rais carbonate-magnetite assemblages revealed low precipitation temperatures (~60°C). Assuming that the CR parent body experienced closed-system alteration, a similar exercise for parallel calcite and magnetite O-isotope arrays yields "global" alteration temperatures of ~55 to 88 °C. These secondary mineral arrays indicate that the O-isotopic composition of the altering fluid evolved upon progressive alteration, beginning near the Al Rais water composition of Δ¹⁷O ~ 1 ‰ and δ¹⁸O ~ 10 ‰, and becoming increasingly ¹⁶O-enriched toward a final fluid composition of Δ¹⁷O ~ -1.2 ‰ and δ¹⁸O ~ -15 ‰.

Petrography, stable isotope compositions, microRaman spectroscopy, and presolar components of Roberts Massif 04133: A reduced CV3 carbonaceous chondrite

Here, we report the mineralogy, petrography, C-N-O-stable isotope compositions, degree of disorder of organic matter, and abundances of presolar components of the chondrite Roberts Massif (RBT) 04133 using a coordinated, multitechnique approach. The results of this study are inconsistent with its initial classification as a Renazzo-like carbonaceous chondrite, and strongly support RBT 04133 being a brecciated, reduced petrologic type >3.3 Vigarano-like carbonaceous (CV) chondrite. RBT 04133 shows no evidence for aqueous alteration. However, it is mildly thermally altered (up to approximately 440 °C); which is apparent in its whole-rock C and N isotopic compositions, the degree of disorder of C in insoluble organic matter, low presolar grain abundances, minor element compositions of Fe,Ni metal, chromite compositions and morphologies, and the presence of unequilibrated silicates. Sulfides within type I chondrules from RBT 04133 appear to be pre-accretionary (i.e., did not form via aqueous alteration), providing further evidence that some sulfide minerals formed prior to accretion of the CV chondrite parent body. The thin section studied contains two reduced CV3 lithologies, one of which appears to be more thermally metamorphosed, indicating that RBT 04133, like several other CV chondrites, is a breccia and thus experienced impact processing. Linear foliation of chondrules was not observed implying that RBT 04133 did not experience high velocity impacts that could lead to extensive thermal metamorphism. Presolar silicates are still present in RBT 04133, although presolar SiC grain abundances are very low, indicating that the progressive destruction or modification of presolar SiC grains begins before presolar silicate grains are completely unidentifiable.

Effect of route of vaccination on the prevention of infectious laryngotracheitis in commercial egg-laying chickens

Commercial egg-laying chickens were vaccinated for infectious laryngotracheitis (ILT) with one of five commercially available vaccines (designated A, B, C, D, and E) on five separate farms by either eyedrop (e), spray (s), or double dose in the water (w) method. Groups were identified by the vaccine designation and the method of vaccination. Birds from the test groups were transferred to an isolation facility and challenged intratracheally 3 wk after vaccination. The remaining birds were given a second vaccination with the original chicken embryo origin vaccine by spray or a chicken embryo origin vaccine if the first vaccine was of tissue culture origin. After challenge, birds were monitored for clinical signs. Those surviving were euthanatized on day 6 postchallenge, and tissues and blood were collected for histopathology, virus isolation, and serology. On the basis of histopathology and enzyme-linked immunosorbent assay (ELISA) results, after one vaccination, all chickens given vaccines by eyedrop were provided better protection than nonvaccinated controls (CTLs). Birds in groups Bs and Ds had lower microscopic lesion scores whereas only birds given Bs had higher ELISA titers than CTLs. Birds in groups As and Cs and groups Bw birds taken from the rear of the barn (r) had microscopic lesion scores that were no different from those of CTLs. These same birds in addition to vaccine Ds had ELISA titers no different from those of CTLs. Of all vaccines, only A given by eyedrop or spray produced higher virus isolation titers than those of CTLs. The remainder of the vaccines produced virus isolation titers that were no different from those of CTLs. After two vaccinations, all groups had lower microscopic lesion scores than CTLs. Only Bw birds from the middle of the barn Bs, EeDs, and AsAs had virus isolation results that were higher than those of CTLs. Only groups BwrBs, CsCs, and DsDs had ELISA titers no different from those of controls. These results suggest that a priming vaccination followed by a booster dose offers better protection against ILT than a single vaccination alone. Vaccine application by eyedrop provides more uniform protection if only one vaccination is given, whereas spray vaccination may serve as an alternative method of vaccination for birds receiving two doses of vaccine.

Pathogenicity and immunogenicity of mynah pox virus in chickens and bobwhite quail

An avian pox virus was isolated from cutaneous proliferative lesions removed from greater hill mynahs (Gracula religiosa) imported from Malaysia. Cutaneous inoculation of specific pathogen-free chickens and bobwhite quail with the mynah pox virus resulted in severe proliferative cutaneous lesions similar to those seen in the naturally infected mynah birds. Microscopically, the reaction in the chickens and quail at sites of virus inoculation was characterized by marked epithelial hyperplasia with ballooning degeneration and formation of cytoplasmic inclusion bodies. Inoculation of conjunctival and oral mucosae of chickens by applying pox virus with a cotton swab did not result in gross or microscopic lesions. In cross-protection studies, chickens and bobwhite quail immunized with either quail, fowl, pigeon, turkey, or psittacine pox vaccines were not protected from challenge with mynah pox virus. Following vaccination of quail and chickens with mynah pox virus vaccine, there was no resistance to challenge by quail, fowl, pigeon, turkey, or psittacine pox viruses. Significant protection against development of lesions following inoculation with mynah pox virus was attained only when the homologous virus was used as a vaccine.