^1,2Oliver Shah,¹Ravit Helled,²Yann Alibert,^2,3Klaus Mezger
The Astrophysical Journal 926, 2 Open Access Link to Article [DOI 10.3847/1538-4357/ac410d]
¹Center for Theoretical Astrophysics and Cosmology, University of Zurich, Switzerland
²Center for Space and Habitability, University of Bern, Switzerland
³Institut für Geologie, University of Bern, Switzerland

Venus’ mass and radius are similar to those of Earth. However, dissimilarities in atmospheric properties, geophysical activity, and magnetic field generation could hint toward significant differences in the chemical composition and interior evolution of the two planets. Although various explanations for the differences between Venus and Earth have been proposed, the currently available data are insufficient to discriminate among the different solutions. Here we investigate the possible range of models for Venus’ structure. We assume that core segregation happened as a single-stage event. The mantle composition is inferred from the core composition using a prescription for metal-silicate partitioning. We consider three different cases for the composition of Venus defined via the bulk Si and Mg content, and the core’s S content. Permissible ranges for the core size, mantle, and core composition as well as the normalized moment of inertia (MoI) are presented for these compositions. A solid inner core could exist for all compositions. We estimate that Venus’ MoI is 0.317–0.351 and its core size 2930–4350 km for all assumed compositions. Higher MoI values correspond to more oxidizing conditions during core segregation. A determination of the abundance of FeO in Venus’ mantle by future missions could further constrain its composition and internal structure. This can reveal important information on Venus’ formation and evolution, and, possibly, the reasons for the differences between Venus and our home planet.

^{9, 1}Jacqueline den Hartogh,¹Maria K. Petö,^9,1,2,3Thomas Lawson,^4,5Andre Sieverding,^1,6Hannah Brinkman,^9,1,2,3Marco Pignatari,^1,7,8Maria Lugaro
The Astrophysical Journal 927, 220 Open Access Link to Article [DOI 10.3847/1538-4357/ac4965]
¹Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH), Konkoly Thege Miklós út 15-17, H-1121 Budapest, Hungary
²E.A. Milne Centre for Astrophysics, Department of Physics and Mathematics, University of Hull, HU6 7RX, UK
³Joint Institute for Nuclear Astrophysics—Center for the Evolution of the Elements, USA
⁴School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
⁵Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6354, USA
⁶Graduate School of Physics, University of Szeged, Dom tér 9, Szeged, 6720, Hungary
⁷ELTE Eötvös Loránd University, Institute of Physics, Budapest 1117, Pázmány Péter sétány 1/A, Hungary
⁸School of Physics and Astronomy, Monash University, VIC 3800, Australia

Isotope variations of nucleosynthetic origin among solar system solid samples are well documented, yet the origin of these variations is still uncertain. The observed variability of ⁵⁴Cr among materials formed in different regions of the protoplanetary disk has been attributed to variable amounts of presolar, chromium-rich oxide (chromite) grains, which exist within the meteoritic stardust inventory and most likely originated from some type of supernova explosion. To investigate if core-collapse supernovae (CCSNe) could be the site of origin of these grains, we analyze yields of CCSN models of stars with initial masses 15, 20, and 25 M_⊙, and solar metallicity. We present an extensive abundance data set of the Cr, Mg, and Al isotopes as a function of enclosed mass. We find cases in which the explosive C ashes produce a composition in good agreement with the observed ⁵⁴Cr/⁵²Cr and ⁵³Cr/⁵²Cr ratios as well as the ⁵⁰Cr/⁵²Cr ratios. Taking into account that the signal at atomic mass 50 could also originate from ⁵⁰Ti, the ashes of explosive He burning also match the observed ratios. Addition of material from the He ashes (enriched in Al and Cr relative to Mg to simulate the make-up of chromite grains) to the solar system’s composition may reproduce the observed correlation between Mg and Cr anomalies, while material from the C ashes does not present significant Mg anomalies together with Cr isotopic variations. In all cases, nonradiogenic, stable Mg isotope variations dominate over the variations expected from ²⁶Al.

^1,2Lisseth Gavilan,³Phay J. Ho,^1,4Uma Gorti,⁵Hirohito Ogasawara,⁶Cornelia Jäger, ¹Farid Salama
The Astrophysical Journal 925, 86 Open Access Link to Article [DOI 10.3847/1538-4357/ac3dfd]
¹NASA Ames Research Center, Space Science & Astrobiology Division, Moffett Field, CA 94035, USA
²Universities Space Research Association (USRA), Columbia, MD 21046, USA
³Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, IL 60439, USA
⁴SETI Institute, Carl Sagan Center, Mountain View, CA 94035, USA
⁵Stanford Synchrotron Radiation Laboratory, P.O. Box 20450, Stanford, CA 94309, USA
⁶Laboratory Astrophysics and Cluster Physics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University & Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany

We present the results of an integrated laboratory and modeling investigation into the impact of stellar X-rays on cosmic dust. Carbonaceous grains were prepared in a cooled (<200 K) supersonic expansion from aromatic molecular precursors, and were later irradiated with 970 eV X-rays. Silicate (enstatite) grains were prepared via laser ablation, thermally annealed, and later irradiated with 500 eV X-rays. Infrared spectra of the 3.4 μm band of the carbon sample prepared with benzene revealed 84% ± 5% band area loss for an X-ray dose of 5.2 ×10²³ eV.cm⁻². Infrared spectra of the 8–12 μm Si–O band of the silicate sample revealed band area loss up to 63% ± 5% for doses of 2.3 × 10²³ eV.cm⁻². A hybrid Monte Carlo particle trajectory approach was used to model the impact of X-rays and ensuing photoelectrons, Auger and collisionally ionized electrons through the bulk. As a result of X-ray ionization and ensuing Coulomb explosions on surface molecules, the calculated mass loss is 60% for the carbonaceous sample and 46% for the silicate sample, within a factor of 2 of the IR band loss, supporting an X-ray induced mass-loss mechanism. We apply the laboratory X-ray destruction rates to estimate the lifetimes of dust grains in protoplanetary disks surrounding 1 M_⊙ and 0.1 M_⊙ G and M stars. In both cases, X-ray destruction timescales are short (a few million years) at the disk surface, but are found to be much longer than typical disk lifetimes (≳10 Myr) over the disk bulk.

¹Marco Fatuzzo,^2,3Fred C. Adams
The Astrophysical Journal 925 56 Open Access Link to Article [DOI 10.3847/1538-4357/ac38a7]
¹Department of Physics, Xavier University, Cincinnati, OH 45207, USA; fatuzzo@xavier.edu
²Department of Physics, University of Michigan, MI 48109, USA
³Department of Astronomy, University of Michigan, MI 48109, USA; fca@umich.edu

Short-lived radioactive nuclei (half-life τ_1/2 ∼ 1 Myr) influence the formation of stars and planetary systems by providing sources of heating and ionization. Whereas many previous studies have focused on the possible nuclear enrichment of our own solar system, the goal of this paper is to estimate the distributions of short-lived radionuclides (SLRs) for the entire population of stars forming within a molecular cloud. Here we focus on the nuclear species ⁶⁰Fe and ²⁶Al, which have the largest impact due to their relatively high abundances. We construct molecular-cloud models and include nuclear contributions from both supernovae and stellar winds. The resulting distributions of SLRs are time dependent with widths of ∼3 orders of magnitude and mass fractions ρ_SLR/ρ_* ∼ 10⁻¹¹–10⁻⁸. Over the range of scenarios explored herein, the SLR distributions show only modest variations with the choice of cloud structure (fractal dimension), star formation history, and cluster distribution. The most important variation arises from the diffusion length scale for the transport of SLRs within the cloud. The expected SLR distributions are wide enough to include values inferred for the abundances in our solar system, although most of the stars are predicted to have smaller enrichment levels. In addition, the ratio of ⁶⁰Fe/²⁶Al is predicted to be greater than unity, on average, in contrast to solar system results. One explanation for this finding is the presence of an additional source for the ²⁶Al isotope.

¹Seonho Kim,¹Kwang Hyun Sung,¹Kyujin Kwak
The Astrophysical Journal 924, 88 Open Access Link to Article [DOI 10.3847/1538-4357/ac35e1]
¹Department of Physics, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic Of Korea

The isotopic compositions of ruthenium (Ru) are measured from presolar silicon carbide (SiC) grains. In a popular scenario, the presolar SiC grains formed in the outskirt of an asymptotic giant branch (AGB) star, left the star as a stellar wind, and joined the presolar molecular cloud from which the solar system formed. The Ru isotopes formed inside the star, moved to the stellar surface during the AGB phase, and were locked into the SiC grains. Following this scenario, we analyze the Nucleosynthesis Grid (NuGrid) data, which provide the abundances of the Ru isotopes in the stellar wind for a set of stars in a wide range of initial masses and metallicities. We apply the C > O (carbon abundance larger than the oxygen abundance) condition, which is commonly adopted for the condition of the SiC formation in the stellar wind. The NuGrid data confirm that SiC grains do not form in the winds of massive stars. The isotopic compositions of Ru in the winds of low-mass stars can explain the measurements. We find that lower-mass stars (1.65 M☉ and 2 M☉) with low metallicity (Z = 0.0001) can explain most of the measured isotopic compositions of Ru. We confirm that the abundance of 99 Ru inside the presolar grain includes the contribution from the in situ decay of 99 Tc. We also verify our conclusion by comparing the isotopic compositions of Ru integrated over all the pulses with those calculated at individual pulses.

¹Hervé Toulhoat,²Viacheslav Zgonnik
The Astrophysical Journal 924, 83 Openb Access Link to Article [DOI 10.3847/1538-4357/ac300b]
¹Sorbonne Université, UPMC, CNRS, Laboratoire de Réactivité de Surface, 4 Place Jussieu, F-75005, Paris, France; herve.toulhoat@orange.fr
² Natural Hydrogen Energy LLC, French Branch: 31 Rue Raymond Queneau, F-92500 Rueil Malmaison, France

By plotting empirical chemical element abundances on Earth relative to the Sun and normalized to silicon versus their first ionization potentials, we confirm the existence of a correlation reported earlier. To explain this, we develop a model based on principles of statistical physics that predicts differentiated relative abundances for any planetary body in a solar system as a function of its orbital distance. This simple model is successfully tested against available chemical composition data from CI chondrites and surface compositional data of Mars, Earth, the Moon, Venus, and Mercury. We show, moreover, that deviations from the proposed law for a given planet correspond to later surface segregation of elements driven both by gravity and chemical reactions. We thus provide a new picture for the distribution of elements in the solar system and inside planets, with important consequences for their chemical composition. Particularly, a 4 wt% initial hydrogen content is predicted for bulk early Earth. This converges with other works suggesting that the interior of the Earth could be enriched with hydrogen.

^1,2KeZhu朱柯,³Martin Schiller,²Frédéric Moynier,³Mirek Groen,⁴Conel M. O’D. Alexander,⁵Jemma Davidson,⁵Devin L.Schrader,⁶Addi Bischoff,³Martin Bizzarro
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.12.014]
¹Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, 12249 Berlin, Germany
²Université Paris Cité, Institut de Physique du Globe de Paris, CNRS UMR 7154, 1 rue Jussieu, Paris 75005, France
³Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5–7, Copenhagen DK-1350, Denmark
⁴Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, Washington, DC 20015, USA
⁵Buseck Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287-6004, USA
⁶Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
Copyright Elsevier

Chondrites are undifferentiated meteorites that can provide information on the compositions of materials in the early solar System, including the building blocks of the terrestrial planets. While most chondrites belong to well-defined groups based on their mineralogy and chemical composition, a minor fraction have unusual characteristics and are classified as ungrouped chondrites. These ungrouped chondrites reflect the diversity of chondritic materials in the early solar system; however, they are not as well studied as grouped meteorites and their origins are poorly understood. In this study, we present high-precision mass-independent Cr, Ca and Mg isotope data for 17 ungrouped chondrites. The ε54Cr and ε48Ca (ε expresses parts per ten thousand mass-independent isotope deviation) data for ungrouped chondrites also provide important constraints for assessing their relationships to the known chondrite groups, and the radiogenic Mg isotope ratios (μ26Mg*) can be used to track the early solar system history. We also present the first high-precision data for a Kakangari (KC) chondrite, an enstatite chondrite, and for four enstatite-rich meteorites. The ε54Cr and ε48Ca values for the KC are -0.44 ± 0.04 and -1.30 ± 0.25, respectively, and ε48Ca value for SAH 97096 (EH3) is -0.19 ± 0.22 that overlaps with that of those of Earth-Moon system and ordinary chondrites. All the carbonaceous chondrite-like (CC) ungrouped chondrites show positive ε54Cr and ε48Ca values, and all the non-carbonaceous chondrite-like (NC) ungrouped chondrites and KCs (also belong to the NC trend) show zero or negative ε54Cr and ε48Ca values. This observation confirms the CC-NC dichotomy for primitive solar system materials. LEW 87232 (KC) also shows the highest 55Mn/52Cr ratio and ε53Cr value amongst all the chondrites. There is a positive trend between 55Mn/52Cr ratios and ε53Cr values among all the chondrites that mostly reflects a mixing between multiple chondritic components. Previously it has been reported that there is a bulk 26Al-26Mg correlation line amongst chondrites. This correlation has been interpreted as being due to mixing of CAIs (high 27Al/24Mg ratios and μ26Mg* values) and other silicate material (e.g., chondrules and matrix). By providing additional 26Al-26Mg chondrite data, we show that there is no 26Al-26Mg correlation line for the chondrites, ruling out the two-endmember (i.e., CAIs and other silicates) mixing model.

^1,2Daohai Li,²Alexander J. Mustill,^2,3Melvyn B. Davies
The Astrophysical Journal 924, 61 Open Access Link to Article [DOI 10.3847/1538-4357/ac33a8]
¹Department of Astronomy Beijing Normal University, No.19, Xinjiekouwai Street, Haidian District, Beijing, 100875, People’s Republic of China; lidaohai@gmail.com, lidaohai@bnu.edu.cn
²Lund Observatory Department of Astronomy and Theoretical Physics Lund University, Box 43, SE-221 00 Lund, Sweden
³Centre for Mathematical Sciences Lund University, Box 118, SE-221 00 Lund, Sweden

White dwarfs (WDs) often show metal lines in their spectra, indicating accretion of asteroidal material. Our Sun is to become a WD in several gigayears. Here, we examine how the solar WD accretes from the three major small body populations: the main belt asteroids (MBAs), Jovian Trojan asteroids (JTAs), and trans-Neptunian objects (TNOs). Owing to the solar mass loss during the giant branch, 40% of the JTAs are lost but the vast majority of MBAs and TNOs survive. During the WD phase, objects from all three populations are sporadically scattered onto the WD, implying ongoing accretion. For young cooling ages ≲100 Myr, accretion of MBAs predominates; our predicted accretion rate ∼106 g s−1 falls short of observations by two orders of magnitude. On gigayear timescales, thanks to the consumption of the TNOs that kicks in ≳100 Myr, the rate oscillates around 106–107 g s−1 until several gigayears and drops to ∼105 g s−1 at 10 Gyr. Our solar WD accretion rate from 1 Gyr and beyond agrees well with those of the extrasolar WDs. We show that for the solar WD, the accretion source region evolves in an inside-out pattern. Moreover, in a realistic small body population with individual sizes covering a wide range as WD pollutants, the accretion is dictated by the largest objects. As a consequence, the accretion rate is lower by an order of magnitude than that from a population of bodies of a uniform size and the same total mass and shows greater scatter.

^1,2,8Thomas C. L. Trueman,^1,3,4,8Benoit Côté,^1,8Andrés Yagüe López,^1,8Jacqueline den Hartogh,^1,2,4,8Marco Pignatari,^1,5Benjámin Soós,^6,7Amanda I. Karakas,^1,5,6Maria Lugaro
The Astrophysical Journal 924, 10 Open Access Link to Article [DOI 10.3847/1538-4357/ac31b0]
¹Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network, Konkoly Thege Miklós út 15-17, H-1121 Budapest, Hungary; thomas.trueman@csfk.mta.hu
²E.A. Milne Centre for Astrophysics, Department of Physics & Mathematics, University of Hull, HU6 7RX, UK
³Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 2Y2, Canada
⁴Joint Institute for Nuclear Astrophysics—Center for the Evolution of the Elements, USA
⁵ELTE Eötvös Loránd University, Institute of Physics, Budapest 1117, Pázmány Péter sétány 1/A, Hungary
⁶School of Physics and Astronomy, Monash University, VIC 3800, Australia
⁷ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia
⁸NuGrid Collaboration http://nugridstars.org.

Analysis of inclusions in primitive meteorites reveals that several short-lived radionuclides (SLRs) with half-lives of 0.1–100 Myr existed in the early solar system (ESS). We investigate the ESS origin of ¹⁰⁷Pd, ¹³⁵Cs, and ¹⁸²Hf, which are produced by slow neutron captures (the s-process) in asymptotic giant branch (AGB) stars. We modeled the Galactic abundances of these SLRs using the OMEGA+ galactic chemical evolution (GCE) code and two sets of mass- and metallicity-dependent AGB nucleosynthesis yields (Monash and FRUITY). Depending on the ratio of the mean-life τ of the SLR to the average length of time between the formations of AGB progenitors γ, we calculate timescales relevant for the birth of the Sun. If τ/γ ≳ 2, we predict self-consistent isolation times between 9 and 26 Myr by decaying the GCE predicted ¹⁰⁷Pd/¹⁰⁸Pd, ¹³⁵Cs/¹³³Cs, and ¹⁸²Hf/¹⁸⁰Hf ratios to their respective ESS ratios. The predicted ¹⁰⁷Pd/¹⁸²Hf ratio indicates that our GCE models are missing 9%–73% of ¹⁰⁷Pd and ¹⁰⁸Pd in the ESS. This missing component may have come from AGB stars of higher metallicity than those that contributed to the ESS in our GCE code. If τ/γ ≲ 0.3, we calculate instead the time (T_LE) from the last nucleosynthesis event that added the SLRs into the presolar matter to the formation of the oldest solids in the ESS. For the 2 M_⊙, Z = 0.01 Monash model we find a self-consistent solution of T_LE = 25.5 Myr.

^1,2Alan E. Rubin,¹Bidong Zhang
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13939]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, 90095-1567 USA
²Maine Mineral & Gem Museum, 99 Main Street, PO Box 500, Bethel, Maine, 04217 USA
Published by arrangement with John Wiley & Sons

Allan Hills A77255, Babb’s Mill (Blake’s Iron), Nordheim, and Chinga are ungrouped ataxitic iron meteorites that are similar to the IAB group of noncarbonaceous-type irons in their concentrations of common and refractory siderophile elements. Mo-isotopic data show that ALHA77255, Nordheim, and Chinga are carbonaceous-type (CC) irons. (The Mo-isotopic composition of Babb’s Mill [Blake’s Iron] has not yet been measured, but it also seems likely to be a CC iron.) Relative to mean IAB irons, these four ataxites are severely depleted in moderately volatile elements: Ga, >99%; Ge, >99%; Cu, 79%–97%; As, 70%–96%; P, 76%–90%. These samples were probably devolatilized by major collisions on separate parent asteroids (consistent with fractional crystallization modeling showing they are unlikely to be derived from the same metallic core). Collisionally induced devolatilization of ALHA77255 likely facilitated the formation of a 5-mm diameter silica–glass spheroid in this meteorite. The spheroid may have formed by a complex process involving impact-induced vaporization of mantle material in its parent asteroid, followed by fractional condensation.