During the last days of this year, Cosmochemistry Papers will be on Christmas break (more or less). Normal service will commence on January, 2nd, 2023 after we have recovered.

Merry Christmas & Happy New Year to everyone!

¹Alexey Potapov,²Maria Elisabetta Palumbo,³Zelia Dionnet,^4,5Andrea Longobardo,¹Cornelia Jäger,²Giuseppe Baratta,^4,5Alessandra Rotundi,⁶Thomas Henning
The Astrophysical Journal 935, 158 Open Access Link to Article [DOI 10.3847/1538-4357/ac7f32]
¹Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany
²INAF-Osservatorio Astrofisico di Catania, Via Santa Sofia 78, I-95123 Catania, Italy
³Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, F-91405, Orsay, France
⁴Dip. Scienze e Tecnologie, Università degli Studi di Napoli “Parthenope,” Centro Direzionale I C4, I-80143 Napoli, Italy
⁵INAF-Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, I-00133 Roma, Italy
⁶Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany

The origin of organic compounds detected in meteorites and comets, some of which could have served as precursors of life on Earth, remains an open question. The aim of the present study is to make one more step in revealing the nature and composition of organic materials of extraterrestrial particles by comparing infrared spectra of laboratory-made refractory organic residues to spectra of cometary particles returned by the Stardust mission, interplanetary dust particles, and meteorites. Our results reinforce the idea of a pathway for the formation of refractory organics through energetic and thermal processing of molecular ices in the solar nebula. There is also the possibility that some of the organic material had formed already in the parental molecular cloud before it entered the solar nebula. The majority of the IR “organic” bands of the studied extraterrestrial particles can be reproduced in the spectra of the laboratory organic residues. We confirm the detection of water, nitriles, hydrocarbons, and carbonates in extraterrestrial particles and link it to the formation location of the particles in the outer regions of the solar nebula. To clarify the genesis of the species, high-sensitivity observations in combination with laboratory measurements like those presented in this paper are needed. Thus, this study presents one more piece of the puzzle of the origin of water and organic compounds on Earth and motivation for future collaborative laboratory and observational projects.

¹Cicero X. Lu et al. (>10)
The Astrophysical Journal 933, 54 Open Access Link to Article [DOI 10.3847/1538-4357/ac70d1]
¹Department of Physics and Astronomy, The Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA; cicerolu@jhu.edu

While β Pic is known to host silicates in ring-like structures, whether the properties of these silicate dust vary with stellocentric distance remains an open question. We re-analyze the β Pictoris debris disk spectrum from the Spitzer Infrared Spectrograph (IRS) and a new Infrared Telescope Facility Spectrograph and Imager spectrum to investigate trends in Fe/Mg ratio, shape, and crystallinity in grains as a function of wavelength, a proxy for stellocentric distance. By analyzing a re-calibrated and re-extracted spectrum, we identify a new 18 μm forsterite emission feature and recover a 23 μm forsterite emission feature with a substantially larger line-to-continuum ratio than previously reported. We find that these prominent spectral features are primarily produced by small submicron-sized grains, which are continuously generated and replenished from planetesimal collisions in the disk and can elucidate their parent bodies’ composition. We discover three trends about these small grains: as stellocentric distance increases, (1) small silicate grains become more crystalline (less amorphous), (2) they become more irregular in shape, and (3) for crystalline silicate grains, the Fe/Mg ratio decreases. Applying these trends to β Pic’s planetary architecture, we find that the dust population exterior to the orbits of β Pic b and c differs substantially in crystallinity and shape. We also find a tentative 3–5 μm dust excess due to spatially unresolved hot dust emission close to the star. From our findings, we infer that the surfaces of large planetesimals are more Fe-rich and collisionally processed closer to the star but more Fe-poor and primordial farther from the star.

¹Alan P. Boss
The Astrophysical Journal 933, 1 Open Access Link to Article [DOI 10.3847/1538-4357/ac6609]
¹Earth & Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC 20015-1305, USA; aboss@carnegiescience.edu

Cook et al. found that iron meteorites have an initial abundance ratio of the short-lived isotope 60Fe to the stable isotope 56Fe of 60Fe/56Fe ∼ (6.4 ± 2.0) × 10−7. This appears to require the injection of live 60Fe from a Type II supernova (SN II) into the presolar molecular cloud core, as the observed ratio is over a factor of 10 times higher than would be expected to be found in the ambient interstellar medium (ISM) as a result of galactic chemical evolution. The supernova triggering and injection scenario offers a ready explanation for an elevated initial 60Fe level, and in addition provides a physical mechanism for explaining the noncarbonaceous–carbonaceous (NC–CC) dichotomy of meteorites. The NC–CC scenario hypothesizes the solar nebula first accreted material that was enriched in supernova-derived nuclides, and then later accreted material depleted in supernova-derived nuclides. While the NC–CC dichotomy refers to stable nuclides, not short-lived isotopes like 60Fe, the SN II triggering hypothesis provides an explanation for the otherwise unexplained change in nuclides being accreted by the solar nebula. Three-dimensional hydrodynamical models of SN II shock-triggered collapse show that after triggering collapse of the presolar cloud core, the shock front sweeps away the local ISM while accelerating the resulting protostar/disk to a speed of several kilometers per second, sufficient for the protostar/disk system to encounter within ∼1 Myr the more distant regions of a giant molecular cloud complex that might be expected to have a depleted inventory of supernova-derived nuclides.

¹Hassan Sabbah,¹Mickaël Carlos,²Peter Jenniskens,³Muawia H. Shaddad,⁴Jean Duprat,⁵Cyrena A. Goodrich,¹Christine Joblin
The Astrophysical Journal 931, 91 Open Access Link to Article [DOI 10.3847/1538-4357/ac69dd]
¹IRAP, Université Toulouse III—Paul Sabatier, CNRS, CNES, F-31028 Toulouse Cedex 4, France
²SETI Institute, Mountain View, CA 94043, USA
³University of Khartoum, Khartoum 11115, Sudan
⁴IMPMC, CNRS-MNHN-Sorbonne Université, 57 rue Cuvier, F-75005 Paris, France
⁵Lunar and Planetary Institute, USRA, Houston, TX 77058, USA

Buckminsterfullerene, C60, is the largest molecule observed to date in interstellar and circumstellar environments. The mechanism of formation of this molecule is actively debated. Despite targeted searches in primitive carbonaceous chondrites, no unambiguous detection of C60 in a meteorite has been reported to date. Here we report the first firm detection of fullerenes, from C30 to at least C100, in the Almahata Sitta (AhS) polymict ureilite meteorite. This detection was achieved using highly sensitive laser desorption laser ionization mass spectrometry. Fullerenes have been unambiguously detected in seven clasts of AhS ureilites. Molecular family analysis shows that fullerenes are from a different reservoir compared to the polycyclic aromatic hydrocarbons detected in the same samples. The fullerene family correlates best with carbon clusters, some of which may have been formed by the destruction of solid carbon phases by the impacting laser. We show that the detected fullerenes are not formed in this way. We suggest that fullerenes are an intrinsic component of a specific carbon phase that has yet to be identified. The nondetection of fullerenes in the Murchison and Allende bulk samples, while using the same experimental conditions, suggests that this phase is absent or less abundant in these primitive chondrites. The former case would support the formation of fullerenes by shock-wave processing of carbonaceous phases in the ureilite parent body. However, there are no experimental data to support this scenario. This leaves open the possibility that fullerenes are an interstellar heritage and a messenger of interstellar processes.

^1,2,3Debanjan Sengupta,¹Paul R. Estrada,¹Jeffrey N. Cuzzi,⁴Munir Humayun
The Astrophysical Journal 932, 82 Open Access Link to Article [DOI 10.3847/1538-4357/ac6dcc]
¹NASA Ames Research Center; Mail Stop 245-3, Moffett Field, CA 94035, USA
²Universities Space Research Association; 7178 Columbia Gateway Drive, Columbia, MD 21046, USA
³NASA Postdoctoral Program (NPP) Fellow
⁴National High Magnetic Field Laboratory and Department of Earth, Ocean and Atmospheric Science, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL, 32310, USA

Rocky bodies of the inner solar system display a systematic depletion of “moderately volatile elements” (MVEs) that correlates with the expected condensation temperature of their likely host materials under protoplanetary nebula conditions. In this paper, we present and test a new hypothesis in which open-system loss processes irreversibly remove vaporized MVEs from high nebula altitudes, leaving behind the more refractory solids residing much closer to the midplane. The MVEs irreversibly lost from the nebula through these open-system loss processes are then simply unavailable for condensation onto planetesimals forming even much later, after the nebula has cooled, overcoming a critical difficulty encountered by previous models of this type. We model open-system loss processes operating at high nebula altitudes, such as resulting from disk winds flowing out of the system entirely, or layered accretion directly onto the young Sun. We find that mass-loss rates higher than those found in typical T-Tauri disk winds, lasting short periods of time, are most satisfactory, pointing to multiple intense early outburst stages. Using our global nebula model, incorporating realistic particle growth and inward drift for solids, we constrain how much the MVE-depletion signature in the inner region is diluted by the drift of undepleted material from the outer nebula. We also find that a significant irreversible loss of the common rock-forming elements (Fe, Mg, Si) can occur, leading to a new explanation of another long-standing puzzle of the apparent “enhancement” in the relative abundance of highly refractory elements in chondrites.

¹János Kodolányi,¹Peter Hoppe,²Christian Vollmer,²Jasper Berndt,³Maren Müller
The Astrophysical Journal 929,107 Open Access Link to Article [DOI 10.3847/1538-4357/ac5910]
¹Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, D-55128 Mainz, Germany; j.kodolanyi@mpic.de
²University of Münster, Institute for Mineralogy, Corrensstrasse 24, D-48149 Münster, Germany
³Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany

We measured the nickel isotope composition of troilites from chondritic meteorites using the NanoSIMS to put constraints on the abundance of iron-60 in the early solar system. The troilites were selected from petrologic type 3 ordinary and carbonaceous chondrites. Based on petrographic observations and mineral chemistry, the troilites targeted for isotope analysis crystallized from melts, most likely in a nebular setting. Our isotope analyses did not reveal any significant correlation between nickel-60 enrichments and Fe/Ni ratios, either in the entire set of troilite grains or in individual troilites. The average inferred initial 60Fe/56Fe ratio of the studied troilites (i.e., the 60Fe/56Fe ratio calculated for the entire troilite population) is 1.05 (±1.48) ×10−8. This value is very similar to those estimated in the past for Semarkona chondrules, angrites, as well as diogenites and eucrites, based on the isotope analyses of bulk samples (10−9–10−8), but about two orders of magnitude smaller than the average initial 60Fe/56Fe ratios inferred previously for Semarkona troilites and many chondrules from ordinary and carbonaceous chondrites (10−7–10−6) using in situ analysis techniques. Based on petrographic evidence, and the generally unequilibrated nature of our samples, as well as on the timing of chondrule formation and planetary evolution, the lack of discernible signs of in situ iron-60 decay in the studied troilites is probably unrelated to metamorphic re-equilibration, and it is also not the result of a late formation of the troilites. We suggest that the highest inferred initial 60Fe/56Fe ratios reported in the literature are probably inaccurate.

¹Tamami Okamoto,¹Shigeru Ida
The Astrophysical Journal 928, 171 Open Access Link to Article [DOI 10.3847/1538-4357/ac4bc1]
¹Earth-Life Science Institute, Tokyo Institute of Technology, Meguro-ku, 152-8550 Tokyo, Japan

The observationally inferred crystalline abundance in silicates in comets, which should have been formed in the outer region of a protoplanetary disk, is relatively high (∼10%–60%), although crystalline silicates would be formed by the annealing of amorphous precursors in the inner disk region. In order to quantitatively address this puzzle, we performed a Monte Carlo simulation of the advection/diffusion of silicate particles in a turbulent disk in a setting based on the pebble accretion model: pebbles consisting of many small amorphous silicates embedded in an icy mantle are formed in the outer disk region, silicate particles are released at the snow line, crystalline silicate particles are produced at the annealing line, silicate particles diffuse beyond the snow line, and they eventually stick to drifting pebbles to return to the snow line. In the simple case without sticking and with steady pebble flux, we show through the simulations and analytical arguments that the crystalline components in silicate materials beyond the snow line are robustly and uniformly ≃5%. On the other hand, in a more realistic case with sticking and with a decaying pebble flux, the crystalline abundance increases to ∼20%–25%, depending on the ratio of the decay to diffusion timescales. This abundance is consistent with the observations. In this investigation, we assume a simple steady-accretion disk. The simulations coupled with the disk evolution are needed for a more detailed comparison with observed data.

^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.