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NASA NTRS2017

Physical Properties of the Stone Meteorites: Implications for the Properties of Their Parent Bodies

The physical properties of the stone meteorites provide important clues to understanding the formation and physical evolution of material in the Solar protoplanetary disk as well providing indications of the properties of their asteroidal parent bodies. Knowledge of these properties is essential for modeling a number of Solar System processes, such as bolides in planetary atmospheres, the thermal inertia of atmosphereless solid body surfaces, and the internal physical and thermal evolution of asteroids and rock-rich icy bodies. In addition, insight into the physical properties of the asteroids is important for the design of robotic and crewed reconnaissance, lander, and sample return spacecraft missions to the asteroids. One key property is meteorite porosity, which ranges from 0% to more than 40%, similar to the range of porosities seen in asteroids. Porosity affects many of the other physical properties including thermal conductivity, speed of sound, deformation under stress, strength, and response to impact. As a result of the porosity, the properties of most stone meteorites differ significantly from those of compact terrestrial rocks, whose physical properties have been used in many models of asteroid behavior. A few physical properties, such as grain density, magnetic susceptibility, and heat capacity are not functions of porosity. Taken together, the grain density and the magnetic susceptibility can be used to classify unweathered or minimally weathered ordinary chondrites. This provides a rapid screening technique to identify heterogeneous samples, classify new samples, and identify misclassified meteorites or interlopers in strewn fields.

Chondritic meteorites↗

NASA NTRSDate not supplied

On the New Optical Constants Database (OCdb) and its Importance for the Interpretation of Observational Data

The Optical Constants database(ocdb.smce.nasa.gov) came online in February 2023 and provides complex refractive indices of laboratory-generated organic refractory materials and ices relevant to (exo) planetary and astrophysical environments.The goal of the OCdb is to centralize published optical constants data to facilitate both their access by the scientific community and their use to analyze observational data returned by space missions and ground-based observatories. Computational tools are also under development to facilitate scientific use of the available OCdb optical constants data sets. Investigators generating laboratory optical constants are therefore encouraged to contribute their data to OCdb in order to increase the availability of their data and to enhance the scientific effectiveness of the database. Optical constants are critical input parameters in models (e.g.,radiative transfer, atmospheric, and reflectance spectral models)that are used to simulate the absorption, reflection, and scattering of light due to solid materials present in planetary and astrophysical environments (planets, their satellites, exoplanets, asteroids, comets, protoplanetary disks, etc.), and are key to the compositional interpretation of observations. We will first present the infrastructure of the OCdb and show how to use and contribute to it. We will introduce the two large NASA projects, namely, the Laboratory Astrophysics Directed Work Package and the NASA Center for Optical Constants, that have been instrumental in (i) developing the OCdb, (ii) generating planetary-and astrophysics-relevant ices and organic refractory materials from gas and ice irradiation in the laboratory, and (iii) determining their optical constants for inclusion in OCdb. We will also present two studies that are making use of these optical constants to interpret observations of Titan’s atmosphere and Pluto’s surface. These studies show the importance of measuring optical constants of laboratory-generated materials, and their impact on the models used to analyze and interpret astronomical observations. These studies also demonstrate the essential importance of such a database and the need for optical constants of a broad range of materials and wavelengths to enable the scientific community and to maximize the scientific return from space missions (e.g., Cassini, New Horizons, SOFIA, JWST).

The Optical Constants database↗

NASA NTRSDate not supplied

Center for Isotope Cosmochemistry and Geochronology at NASA Johnson Space Center

The Center for Isotope Cosmochemistry and Geochronology (CICG) at the NASA Johnson Space Center, led by Justin Simon, applies novel elemental and isotopic analytical techniques to understand solar system formation, from processes occurring during the earliest Solar Nebula, to the evolution of planetary bodies during planet formation and differentiation. CICG consists of an integrated suite of labs including dedicated spaces for specialized handling and preparation of meteorites and planetary return samples, metal-free clean chemistry, and mass spectrometry. In addition to a Thermo-Scientific Triton thermal ionization mass spectrometer (TIMS) for high precision isotopic analyses in processed samples, CICG houses two additional mass spectrometry instruments with added laser ablation capabilities for high spatial resolution in-situ measurements: (1) a Thermo-Scientific Element-XR inductively coupled mass spectrometer (ICP-MS) with a Teledyne Photon Machines Analyte Excite+ laser ablation system, and (2) a Nu Sapphire 1700 multi-collector ICP-MS, a large geometry instrument with a multi-pole collision cell for interference removal, with an Applied Spectra J200 tandem laser induced breakdown spectroscopy (LIBS) femto-second laser ablation system. We detail the analytical capabilities of CICG in the context of current and future research projects related to the studies of protoplanetary disk evolution via early-formed Solar System solids, volatile abundances and distribution within the inner solar system, and geochemical and temporal investigations related to planet formation and differentiation. We also highlight opportunities through the relationship with the Center of the Advancement of Space Safety and Mission Assurance Research (CASSMAR) at the University of Texas at El Paso. CICG is open to collaborations and participates in the NASA Facility for Astromaterials Research (NFAR) program, which accepts research proposals for access to the unique facility capabilities.

Jacob B. Setera↗

NASA NTRS2023

Investigating the Impact of Metallicity on Star Formation in the Outer Galaxy. I. VLT/KMOS Survey of Young Stellar Objects in Canis Major

The effects of metallicity on the evolution of protoplanetary disks may be studied in the outer Galaxy where the metallicity is lower than in the solar neighborhood. We present the VLT/KMOS integral field spectroscopy in the near-infrared of∼120 candidate young stellar objects (YSOs) in the CMa-ℓ224 star-forming region located at a Galactocentric distance of 9.1 kpc. We characterise the YSO accretion luminosities and accretion rates using the hydrogen Brγemission and find the median accretion luminosity of log (Lacc) =−0.82+0.80−0.82L⊙.Based on the measured accretion luminosities, we investigate the hypothesis of star formation history in the CMa-ℓ224. Their median values suggest that Cluster C, where most of YSO candidates have been identified, might be the most evolved part of the region. The accretion luminosities are similar to those observed toward low-mass YSOs in the Perseus and Orion molecular clouds, and do not reveal the impact of lower metallicity. Similar studies in other outer Galaxy clouds covering a wide range of metallicities are critical to gain a complete picture of star formation in the Galaxy

Dominika Itrich↗

NASA NTRSDate not supplied

Early History of the Solar System Revealed By Calcium-48 Heterogeneity in Calcium-Aluminium-Rich Inclusions

Introduction: Calcium-aluminum-rich inclusions (CAIs) are the earliest formed solids in the solar system. Although the mineralogy of CAIs is consistent with condensation from a solar composition gas, textural, elemental and isotopic signatures point to CAIs having more complicated thermal histories rather than simply being primary condensates. Untangling the condensation record in these refractory inclusions and the associated physicochemical environment, can provide insights into temporal and/or spatial reservoirs in the protoplanetary disk where solids were forming.

R M G Armytage↗

NASA NTRSDate not supplied

Coordinated Analysis of Isotopically Anomalous Nanoglobules and Insoluble Organic Matter in Quick-Look Samples From Asteroid Bennu

Spectral characterization of B-type asteroid Bennu by the Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft indicated abundant organic matter with similarities to insoluble organic matter (IOM) in meteorites. IOM in chondritic samples occurs in multiple forms, including a fluffy morphology and submicron-sized rounded nanoglobules. Isotopic anomalies in H, C, and N have been observed in both morphologies and are postulated to result from low-temperature chemical reactions in the molecular cloud or outer protoplanetary disk [e.g., 2,3]. We tested the hypothesis that Bennu also contains such isotopically anomalous organic matter by conducting coordinated in situ analysis of “quick-look” samples collected from the avionics deck of the OSIRIS-REx sample canister. This study expands our understanding of the fundamental nature of Bennu and its pre-accretionary environment by investigating the morphologies and isotopic distribution of presolar organic matter in Bennu.

A N Nguyen↗

NASA NTRS2024

Bulk Major and Trace Elemental Composition of an Aggregate Sample From Asteroid Bennu

On September 24, 2023, NASA’s OSIRIS-REx mission returned a capsule to Earth carrying material from asteroid Bennu. This event was the first time a U.S. mission delivered pristine samples from an asteroid and is the largest asteroid sample return to date. As these samples represent some of the oldest, most primitive, and pristine materials available to us, and which originate from a known and well-studied asteroid, they allow us a rare opportunity to gain a better understanding of the formation and evolution of our solar system. Key to understanding the material returned from asteroid Bennu is establishing its bulk chemical composition. Previous studies have shown that each chondrite group has a distinct elemental composition. For the carbonaceous chondrites specifically, each group exhibits a distinct pattern of moderately and highly volatile elemental depletions, relative to CI chondrites. CI chondrites are considered the most primitive chondrite group and broadly represent the solar photosphere composition. The two most striking features of these depletion patterns is that the moderately volatile element depletions increase with decreasing 50% condensation temperature and then plateau out at abundances that roughly correlate with matrix abundance. Due to these distinctive patterns, bulk elemental composition has become an important classification tool for establishing the different chondrite groups and the connections between them. As such, determining the bulk chemical composition of the Bennu aggregates will help to test two mission hypothesis: “Bennu’s bulk elemental composition reflects that of its main parent asteroid and is similar to the composition of the Sun, with depletions in moderately to highly volatile elements” and “Bennu’s dominant lithologies are comparable in bulk mineralogy, petrology, and composition to the most aqueously altered carbonaceous chondrites” . Furthermore as the carbonaceous and non-carbonaceous chondrites are thought to have likely formed in the inner and outer protoplanetary disk, respectively (e.g., [8]), determining the bulk chemical compositions of the Bennu aggregates will also help test the major mission hypothesis that “Bennu's parent body formed beyond the snow line by accretion of material in the pro-toplanetary disk” . Regarding chondrite formation, observed elemental patterns have been successfully used to model how the mixing of volatile-rich and volatile-poor chondritic components can produce the observed carbonaceous chondrites groups. They have also been significant in investigating how volatilization processes influenced chondrite formation. As such, establishing bulk chemical compositions of the pristine Bennu samples is vital for understanding the asteroid, and solar system formation. To begin this processes, we analyzed the bulk major and trace elemental compositions of Bennu aggregates.

P Koefoed↗

NASA NTRS2024

Investigating Bennu’s Volatile Accretion History Through Step-Heating N-Ne-Ar Analyses of Single Aggregate Particles

NASA’s OSIRIS-REx spacecraft delivered a sample from the carbonaceous asteroid (101955) Bennu to Earth on September 24, 2023. Since Bennu presumably accreted in the outer protoplanetary disk, beyond Jupiter’s orbit, the collected material is expected to be rich in highly volatile elements such as H, C, N, and noble gases—similar to Ivuna-type (CI) carbonaceous chondrites and material from asteroid (162173) Ryugu returned by JAXA’s Hayabusa2 spacecraft. This type of material may have contributed to the volatile inventory of Earth and the other terrestrial planets. Bulk CI chondrites record a narrow range of δ 15 N values (i.e., the permil difference from the atmospheric 15 N/ 14 N ratio), averaging between +42 and 49‰. In contrast, recent analyses at CRPG’s noble gas facility revealed that two pelletized Ryugu samples have lower δ 15 N values of +18.1 ± 0.9‰ and +19.5 ± 0.9‰. Together with the low measured N abundances, this observation suggests that Ryugu has lost a 15 N-rich, labile organic phase due to pervasive aqueous alteration. Subsequent high-resolution step-heating analyses of an additional Ryugu particle demonstrated that the δ 15 N value varies significantly during successive extraction steps (between +1.0 ± 1.0‰ and 65.8 ± 1.1‰); the variable N isotopic composition points to the presence of several isotopically distinct N-carrier phases in CI-type material. Here, we report preliminary N-Ne-Ar results obtained for individual particles from an aggregate Bennu sample using the Noblesse-HR (Nu Instruments) noble gas mass spectrometer at CRPG’s noble gas facility. In a companion abstract, we will present the noble gas (He, Ne, Ar, Kr, Xe) characteristics of other aggregate particles determined with a HELIX MC Plus. Whereas the abundance and isotopic composition of noble gases permit detection of various presolar phases and the so-called phase Q, as well as quantification of solar wind–derived and cosmogenic components, the abundance and isotopic composition of N are expected to provide further insights into the origin and evolution of N-bearing phases in carbonaceous asteroids.

E Füri↗

NASA NTRSDate not supplied

Noble Gases in Individual Particles From Bennu: Investigating the Origin of Gas-Rich Asteroidal Material

One of the driving hypotheses of the OSIRIS-REx mission [1] is that B-type asteroid Bennu formed beyond the snow line by accretion of material of the protoplanetary disk. Hence Bennu is expected to be rich in highly volatile elements. Among them, noble gases are chemically inert and their abundances and isotope compositions are shaped by physical processes such as radioactivity, irradiation, and isotope fractionation [2]. Hence studying the noble gas composition of Bennu's grains can contribute to testing Hypotheses 4 (formation beyond the snow line), 5 (geological activity), and 6 (catastrophic disruption) of the OSIRIS-REx mission [1]. Here we report preliminary data obtained on particles from asteroid Bennu using our all-noble-gas (He to Xe) analytical system installed at the Centre de Recherches Pétrographiques et Géochimiques (CRPG) Nancy (France) [3]. A companion presentation presents nitrogen-Ne-Ar data [4].

B. Marty↗

NASA NTRS2024

Percolative Sulfide Core Formation in Oxidized Meteorite Parent Bodies

Most models of planetary differentiation involve the formation of metallic cores during or after extensive silicate melting, but some volatile-rich reservoirs in the protoplanetary disk did not accrete substantial amounts of Fe,Ni-metal. Instead, their potential core-forming assemblages were dominated by Fe,Ni-sulfides and oxides due to high ƒ O 2 and ƒ S 2 . Derivative melts from these assemblages may have been capable of percolative migration leading to core formation prior to silicate melting. However, no direct evidence for this process has been reported in meteoritic literature. Similarly, while many iron meteorites are thought to represent cores of their respective parent bodies, no direct evidence for Fe,Ni-sulfide/oxide cores have been reported to-date. The most promising potential for such evidence may be found in the anomalous noble metal trace element proportions of restitic oxidized primitive achondrites (i.e., brachinites, log ƒ O 2 ~IW-1), which are similar to those found in sulfides of Rumuruti-type chondrites (RCs) that contain only trace amounts of Fe,Ni-metal at log ƒ O 2 ≥ IW-1. This work addresses the following outstanding questions: (1) Are molten sulfides in oxidized meteorite assemblages capable of percolative melt migration? (2) How is this process recorded in the noble metal (i.e., siderophile/chalcophile) trace element geochemistry of relevant meteorites? (3) Did O,S-rich meteorite parent bodies form sulfide cores?

S. D. Crossley↗

NASA NTRS2024

Search for Presolar Materials and Isotopically Anomalous Diffuse Insoluble Organic Matter in Samples From Asteroid 101955 Bennu

Carbonaceous asteroids allow us to study the original materials that formed the planets in the protoplanetary disk. They contain organic matter and (sub-)micrometer-size dust grains, called presolar grains, that condensed in the circumstellar envelopes of evolved stars and the ejecta of stellar explosions, such as novae and supernovae, before the formation of our Solar System. The isotopically anomalous organics are thought to have formed in the interstellar medium and the early Solar System. Whereas presolar grains provide insight into the building blocks of our Solar System, studying organics can help us understand the origin of life on Earth. These organics might have contributed to ingredients that helped life emerge. The return of samples from asteroid 101955 Bennu by NASA’s Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission gives us a new opportunity to elucidate the formation mechanism(s) and evolution of organics, as well as the abundance and distribution presolar grains in carbonaceous asteroids. Here, we report on our ongoing work to characterize the isotopic and chemical compositions, microstructure, distribution, and abundance of insoluble organic matter (IOM) and presolar grains in Bennu samples. This work supports hypotheses 2 and 3 of the OSIRIS-REx Sample Analysis Plan.

P. Haenecour↗

NASA NTRSDate not supplied

Anhydrous Primary Minerals in Ryugu, Ivuna, and Bennu

Samples returned from asteroid Ryugu are chemically and mineralogically similar to CI chondrites [e.g., 1–3]. Both are predominantly composed of low-temperature aqueously formed secondary minerals, whereas high-temperature anhydrous primary minerals, such as olivine, low-Ca pyroxene, spinel, and hibonite, are rarely present. Using secondary ion mass spectrometry (SIMS; Cameca ims-1280HR at Hokkaido University), we performed O [4] and Al–Mg [5] isotope measurements of anhydrous primary minerals in samples of Ryugu and the Ivuna CI chondrite to constrain their origin.Anhydrous primary minerals in our samples of Ryugu and Ivuna occur mostly as monomineralic isolated grains embedded in hydrated matrix. Their O-isotope compositions are distributed along the slope-1 line on the O three-isotope diagram and range from Δ17O ~ –23 to 0‰. Mg-Al spinel grains are 16O-rich (Δ17O ~ –23‰). Low-Ca pyroxene grains are 16O-poor (Δ17O ~ –5‰). Olivine grains show a bimodal distribution of O-isotope composition:10 of 34 grains measured are 16O-rich (Δ17O ~ –23‰) and 24 grains are 16O-poor (Δ17O ~ –7 to 0‰). We found refractory inclusions composed of Mg-Al spinel and hibonite, one from Ryugu and one from Ivuna. Also, in Ivuna, we found an amoeboid olivine aggregate ( AOA) composed of olivine, diopside, anorthite, and Mg-Al spinel and an inclusion composed of olivine and Mg-Al spinel. The minerals in all of these inclusions are 16O-rich (Δ17O ~ –24‰).The 16O-rich grains and inclusions are mineralogically and O-isotopically similar to calcium-aluminum–rich inclusions (CAIs) and AOAs reported in other carbonaceous chondrites [6, 7]. In addition, the initial 26Al/27Al ratios of the two spinel-hibonite inclusions are inferred as ~4.4 × 10–5, also similar to most CAIs in carbonaceous chondrites [6, 8]. The range of Δ17O values for the 16O-poor olivine and low-Ca pyroxene grains is consistent withthat of these minerals in chondrules in most carbonaceous chondrites [9]. Moreover, the most frequent Δ17O value (–6‰) for Mg-rich (Mg# > 97) olivine grains is identical to those for chondrules. Although CI chondrites and Ryugu samples are devoid of chondrules, the 16O-poor grains most likely represent fragments of chondrule-like objects. The presence of both 16O-poor chondrule-like and 16O-rich refractory inclusion–like minerals in Ryugu and Ivuna suggests that some of their building blocks are similar to those of other carbonaceous chondrite groups. They both probably formed in the inner solar protoplanetary disk and were subsequently transported outward.Preliminary data for petrography of asteroid Bennu samples and chemical and isotopic compositions of theiranhydrous primary minerals will also be presented in the meeting.

N Kawasaki↗

NASA NTRS2024

Multiple Probe Measurements at Uranus Motivated By Spatial Variability

Predictably, a major motivation for multiple atmospheric probe measurements at Uranus is the understanding of dynamic processes that create and maintain spatial variation in thermal structure, composition, and horizontal winds. But origin questions---regarding the planet's formation and evolution, and conditions in the protoplanetary disk---are also major science drivers for multiprobe exploration. Spatial variation in thermal structure reveals how the atmosphere transports heat from the interior, and measuring compositional variability in the atmosphere is key to ultimately gaining an understanding of the bulk abundances of several heavy elements. We review the current knowledge of spatial variability in Uranus' atmosphere, and we outline how multiple probe exploration would advance our understanding of this variability. The other giant planets are discussed, both to connect multiprobe exploration of those atmospheres to open questions at Uranus, and to demonstrate how multiprobe exploration of Uranus itself is motivated lessons learned about the spatial variation at Jupiter, Saturn, and Neptune. We outline the measurements of highest value from miniature secondary probes (which would complement more detailed investigation by a larger flagship probe), and present the path toward overcoming current challenges and uncertainties in areas including mission design, cost, trajectory, instrument maturity, power, and timeline.

Uranus↗

NASA NTRSDate not supplied

The Nucleosynthetic Heritage of Bennu

The OSIRIS-REx mission sampled the B-type asteroid Bennu and delivered 121.6 g of material to Earth in September 2023. Nucleosynthetic isotope variations are powerful tracers that can be used to establish relationships between different meteorite groups and the returned samples. They can also constrain the samples’ nucleosynthetic heritage, as well as mixing and reservoir formation in the protoplanetary disk. Nucleosynthetic variations reflect the heterogeneous distribution of isotopically distinct dust in the disk, and as such, they provide evidence for the formation of meteorite parent bodies from isotopically distinct dust reservoirs. They are thus also a means to identify exogenous clasts in Bennu materials. Here, we report Ti and Fe isotope data obtained from Bennu samples and carbonaceous chondrites. We also present Ti isotope data for hand-picked matrix from CV and CR chondrites. An isotopic dataset was obtained on aggregate sample OREX-803015-100 consisting of particles typically <500 μm; therefore, its composition represents an average for Bennu materials. A 20.66 mg aliquot was dissolved at Washington University, St. Louis. From this, 5 mg was analysed for Ti and Fe isotopes on a NeptunePlus MC-ICPMS at ETH Zurich; data from a separate aliquot, analysed at Lawrence Livermore National Laboratory, are reported in a companion abstract. Our results demonstrate a close relationship of Bennu to CI and Ryugu samples and therefore a formation outside the snowline, as hypothesized by the mission. Furthermore, the 50 Ti data from the CV and CR matrix fall consistently below the CI and Bennu values, indicating the presence of a uniform matrix mixed with ⁓0.1–0.7% of refractory inclusions in CIs and Bennu.

M. Schönbächler↗

NASA NTRS2024

Presolar Grains in Bennu: Constraints From C and N Isotopic Compositions

Primitive chondrites, including CI and CM types, are known to contain a rich variety of presolar grains that were seeded into the protoplanetary disk from neighboring stars and stellar objects prior to aggregation into asteroidal parent bodies. Stepped combustion using the FINESSE instrument at the Open University (OU) was employed to determine whether material from Bennu contains populations of presolar grains similar to those of CI and CM chondrites as well as recently returned samples from Ryugu.

M M Grady↗

NASA NTRS2024

Hydrogen Isotopic Composition of Hydrous Minerals in Particles From Bennu

On September 24, 2023, NASA’s OSIRIS-REx mission delivered to Earth ~121 g of pristine carbonaceous regolith from asteroid Bennu. A first series of mineralogical observations and chemical/isotopic analyses of Bennu aggregate samples (fine to coarse particles up to a few mm) revealed that this material resembles the most chemically primitive chondrites and the samples returned by the JAXA’s Hayabusa2 mission from the carbonaceous asteroid Ryugu. Laboratory studies have confirmed the story gleaned from the spacecraft encounter that Bennu’s rock fragments underwent extensive aqueous alteration and are predominantly composed of hydrated minerals (serpentine, smectite) and other secondary minerals (e.g., magnetite, carbonates). The secondary phases were likely formed under the presence of liquid water on Bennu’s parent asteroid. The isotopic compositions of hydrous minerals and secondary phases can increase our understanding of the source and distribution of water and volatile elements in the protoplanetary disk [e.g., 5-8]. However, direct estimates of the hydrogen isotopic ratios (D/H) in hydrous minerals cannot be obtained easily in primitive rocks due to the difficulty in estimating the organic matter (OM) contribution to the whole H budget. In order to obtain hints on the initial constituents of Bennu’s parent asteroid and to test if Bennu's parent asteroid have formed beyond the snow line (hypothesis 4 of [9]), we measured the D/H and C/H ratios in chondritic matrices by secondary ion mass spectrometry (SIMS) and obtain information on the D/H ratio of water retained in the hydrated minerals. The method also gives clues on the hydrogen isotope variability among different Bennu rock fragments made available for measurement.

L Piani↗

NASA NTRS2024

Genetic Relationships and the Nucleosynthetic Heritage of the Asteroid Bennu

The OSIRIS-REx sample return mission visited the B-type asteroid Bennu and delivered 121.6 gof pristine material to Earth in September 2023. Genetic links between this pristine material and different meteorite groups can be determined using nucleosynthetic isotope variations. These variations reflect the heterogeneous distribution of isotopically distinct dust from different stellar environments within the protoplanetary disk. They can therefore be used to constrain different formation locations of parent asteroids [e.g., 1]. In addition, isotope variations are powerful tracers to establish the nucleosynthetic heritage of returned samples [e.g., 2] and to evaluate mixing and reservoir formation within the disk. Here we present nucleosynthetic Ti and Fe isotope data for samples from Bennu and several carbonaceous chondrites. We also report the Ti isotope composition of hand-picked matrix fractions from CR and CV meteorites.

M Rüfenacht↗

NASA NTRS2024

Accretion of the earliest inner Solar System planetesimals beyond the water snowline

How and where the first generation of inner Solar System planetesimals formed remains poorly understood. Potential formation regions are the silicate condensation line and water snowline of the solar protoplanetary disk. Whether the chemical compositions of these planetesimals align with accretion at the silicate condensation line (water-free and reduced) or water snowline (water-bearing and oxidized) is, however, unknown. Here we use the Fe/Ni and Fe/Co ratios of magmatic iron meteorites to quantify the oxidation states of the earliest planetesimals associated with non-carbonaceous (NC) and carbonaceous (CC) reservoirs, representing the inner and outer Solar System, respectively. Our results show that the earliest NC planetesimals contained substantial amounts of oxidized Fe in their mantles (3–19 wt% FeO). In turn, we argue that this required the accretion of water-bearing materials into these NC planetesimals. The presence of substantial quantities of moderately and highly volatile elements in their parent cores is also inconsistent with their accretion at the silicate condensation line and favours, instead, their formation at or beyond the water snowline. Similar oxidation states in the early formed parent bodies of NC iron meteorites and those of NC achondrites and chondrites with diverse accretion ages suggest that the formation of oxidized planetesimals from water-bearing materials was widespread in the early history of the inner Solar System.

Damanveer S. Grewal↗