¹L.C. Chaves,¹M.S. Thompson,²M.J. Loeffler,³C.A. Dukes,⁴P.S. Szabo,¹B.H.N. Horgan 
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115634]
¹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907, United States of America
²Department of Physics and Astronomy, Northern Arizona University, 527 South Beaver Street, Flagstaff, AZ 86011, United States of America
³Materials Science and Engineering, University of Virginia, 395 McCormick Road, Charlottesville, VA 22904, United States of America
⁴Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, United States of America
Copyright Elsevier

Magnetite is a relevant mineral component of asteroids as it has been identified in carbonaceous chondrites, on the surface of asteroid Bennu through remote sensing observations, and in samples returned from asteroid Ryugu. However, the effects of space weathering processes on magnetite have not yet been explored. To investigate how this mineral phase responds to space weathering, here we simulate micrometeoroid bombardment and solar wind irradiation of magnetite using pulsed laser and ion irradiation experiments. We performed X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and visible to near-infrared (VNIR) reflectance spectroscopy analyses to characterize the chemical, microstructural, and spectral response of magnetite to simulated space weathering. In addition, we carried out ion impact simulations using the SDTrimSP software to evaluate the calculated response of magnetite to 1 keV H⁺ and 4 keV He⁺ ions and compared these results to our XPS and TEM results. Ion irradiation simulated ~750 years on the surface of asteroid Bennu, with a solar-wind appropriate total H:He fluence ratio (~24). Within this time, depletion of O was observed with H⁺ and He⁺ ion irradiation, with significantly greater change via protons due to the larger fluence, where preferential sputtering promotes the formation of a metallic iron layer at the magnetite surface. This suggests that solar wind ions act as reducing agents on Fe oxides, with a fraction remaining implanted in these phases. Indeed, we observe elongated defects contained in a crystalline rim created by He⁺ implanted ions in the TEM. Pulsed laser irradiation, analogous to micrometeoroid impacts, generates melts on the surface of the magnetite grains. The impact melts and H⁺-generated metallic iron rims both result in increased VNIR spectral reflectance, but lower fluence He⁺ implantation has no significant spectral effect. These results suggest that space weathered magnetite could contribute to bright regions detected in remote sensing analyses of the Ryugu and Bennu surfaces by the Hayabusa2 and OSIRIS-REx missions and will contribute to the identification and interpretation of space weathered magnetite in returned samples retrieved from both asteroids.

¹Ziyan Han,^1,2,3Hejiu Hui,^1,2Haizhen Wei,^1,2Weiqiang Li
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2023.05.007]
¹State Key Laboratory of Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
¹CAS Center for Excellence in Comparative Planetology, Hefei 230026, China
³CAS Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Copyright Elsevier

The Moon is depleted in volatile elements and compounds, and lunar samples exhibit a wide range of Cl isotopic compositions, which is believed to result from the volatilization of metal chlorides (e.g., NaCl, KCl, and FeCl2). However, the Cl isotopic fractionation behavior during volatilization is not well constrained, particularly for metal chlorides. Furthermore, the effect of metal chloride evaporation on metal isotopes is poorly known. In the present study, we performed NaCl and KCl sublimation experiments to study Cl and K isotopic fractionations at temperatures ranging from 923 K to 1061 K and at pressures of 7×10–5 bar to 1 bar in an N2 atmosphere. The isotope fractionation factors of 37/35Cl(αgas–solid) from NaCl sublimation experiments are 0.9985±0.0002, 0.9958±0.0004, and 0.99807±0.00004 at 1, 10–2, and 7×10–5 bar, respectively. Those of 41/39K(αgas–solid) and 37/35Cl(αgas–solid) from KCl sublimation experiments are 0.99884±0.00004 and 0.9988±0.0003 at 1 bar, 0.9977±0.0002 and 0.9972±0.0003 at 10–2 bar, and 0.9989±0.0002 and 0.9989±0.0001 at 7×10–5 bar, respectively. Chlorine and K isotopes fractionate more at 10–2 bar than at 7×10–5 bar and 1 bar. The saturation index in all the sublimation experiments was >95%, which resulted in near-equilibrium isotopic fractionation at the sublimation interface. Therefore, the isotopic fractionation was controlled by mass transfer processes in the gas and solid phases. The isotopic fractionation at 10–2 bar was controlled by the chemical diffusion of sublimated gas in an N2 atmosphere with almost no convection effect, (i.e., Pe number close to zero), whereas the isotopic fractionation at 1 bar was suppressed by atmospheric convection with a turbulence factor of 0.4±0.1 (i.e., Pe number >1). The extremely high sublimation rate and the very slow diffusion in the sublimating solid at 7×10–5 bar suppressed isotopic fractionations. Based on our experimental results, calculations using Cl/K and Na/K in lunar materials reveal that degassing of KCl contributed very little (<0.2‰) to the K isotopic fractionation (>0.58‰) during lunar magma ocean degassing. The Cl isotopic fractionation factor from lunar samples is similar to our results at 10–2 bar. This similarity of Cl isotope fractionation indicates that there may have been a transient atmosphere above the lunar magma ocean.

¹Noriyuki KAWASAKI,²Daiki YAMAMOTO,³Sohei WADA,¹Changkun PARK,³Hwayoung KIM,⁴Naoya SAKAMOTO,^1,4Hisayoshi YURIMOTO
Meteoritics & Planetary Science (in Press) Link to Article [doi: 10.1111/maps.13989]
¹Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
²Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
³Division of Earth-System Sciences, Korea Polar Research Institute, Incheon, Republic of Korea
⁴Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo, Japan
Published by arrangement with John Wiley & Sons

Al–Mg mineral isochron studies using secondary ion mass spectrometry (SIMS)have revealed the initial26Al/27Al ratios, (26Al/27Al)0, for individual Ca-Al-rich inclusions(CAIs) in meteorites. We find that the relative sensitivity factors of27Al/24Mg ratio forSIMS analysis of hibonite, one of the major constituent minerals of CAIs, exhibit variationsbased on their chemical compositions. This underscores the critical need for usingappropriate hibonite standards to obtain accurate Al-Mg data. We measured the AlMgmineral isochron for hibonite in a fine-grained CAI (FGI) from the Northwest Africa 8613reduced CV chondrite by SIMS using synthesized hibonite standards with27Al/24Mg of~30,~100, and~400. The obtained mineral isochron of hibonite in the FGI yields (26Al/27Al)0of(4.730.09)9105, which is identical to that previously obtained from the mineralisochron of spinel and melilite in the same FGI (Kawasaki et al., 2020). The uncertainties of(26Al/27Al)0indicate that the constituent minerals in the FGI formed within~0.02 Myr inthe earliest solar system. The disequilibrium O-isotope distributions of the minerals in theFGI suggest that the O-isotope compositions of the nebular gas from which they condensedunderwent a transitional change from16O-rich to16O-poor within~0.02 Myr in the earliestsolar system. Once formed, the FGI may have been removed from the forming regionwithin~0.02 Myr and transported to the accretion region of the parent body.

¹M. Fastelli,²B. Schmitt,²P. Beck,²O. Poch,¹A. Zucchini,¹F. Frondini,¹P. Comodi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115633]
¹Department of Physics and Geology, University of Perugia, I-06123 Perugia, Italy
²Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
Copyright Elsevier

We analyse the quantitative effects of viewing geometry variations on the near-infrared reflectance spectra of mascagnite-(NH4)2SO4 and salammoniac-NH4Cl samples. Bi-directional reflectance spectra are collected in the 1–4.2 μm range considering a set of 3 incidence (i) angles (i = 0°; 30°; 60°) and 9 emergence (e) angles between −70° and 70° at room temperature and computed with respect to the normal direction. The NH4+ overtone and combinations bands located at ~1.09, 1.32, 1.62, 2.04, 2.2 and 3.05 μm are experimentally investigated. The bidirectional reflectance spectra of these samples show significant variations with the observation geometry in terms of reflectance values, spectral slope, and absorption bands parameters. The band positions remain essentially unchanged by varying the incident and emergence angles. On the other hand, bands’ area and depth show the highest variability for i ≥ 30° and e greater than ±40°(up to a factor 2.3 in relative mean variation). The area and depth parameters of these bands show a dual behaviour: (i) for the weak-medium spectral features below 2 μm the area and depth decrease as the phase angle increases. (ii) The strong spectral features above 2 μm increase their values only at phase angles above 90°, but also at low phase angles for high incidences, i ≥ 30°. This behaviour is linked both to the non-linear radiative transfer in particulate media and to the way the band depth and area are defined, relative to the local continuum. We observe important dependence (up to ~60% relative mean variation) of band depth and area on the incidence angle, up to 60°, compared to moderate variation with emergence angles (up to ~20% relative mean variation). Furthermore, the ~3 μm features becomes more saturated at ±70° emergence angles. A general trend of spectral bluing with change in observation geometry is observed. The current dataset is a contribution in the framework of present and future space missions focused on understanding the nature and quantification of ammonium-bearing minerals on icy bodies. The NH4+ − bearing minerals identification could provide information on: (i) ocean/brine compositions, (ii) possible explanations of geological phenomena and (iii) implications for biological activity.

¹C.P. Haupt,¹C.J. Renggli,¹M. Klaver,¹E.S. Steenstra,¹J. Berndt,¹A. Rohrbach,¹S. Klemme
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115625]
¹Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Münster 48149, Germany
Copyright Elsevier

The origin of young Chang’e 5 (CE5) lunar basalts is highly debated. We present results from high-pressure, high-temperature (P-T) phase equilibria experiments, and from petrological modeling, to constrain the depth and temperature of the source of these unique mare basalts. The experimental results indicate that the CE5 basalts could have formed either by melting clinopyroxene and Fesingle bondTi oxide-rich cumulates in the shallow lunar mantle, or by extreme fractional crystallization of a hot Mg-rich parental melt. Our findings corroborate the local preservation of significant heat (of at least 1200 °C) in the lunar mantle that is needed to generate basaltic melts of CE5 compositions at 2 Ga. We argue that the CE5 basalts are most likely formed by melting of Fe and Ti-rich cumulates in the shallow lunar mantle as extreme fractional crystallization of olivine and plagioclase from picritic parental melts requires too high temperatures in the lunar mantle (> 1500 °C) at ~2 Ga.

¹Marceau Lecasble,¹Sylvain Bernard,¹Jean-Christophe Viennet,¹Isis Criouet,¹Laurent Remusat
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115603]
¹Muséum National d’Histoire Naturelle, Sorbonne Université, CNRS UMR 7590, IMPMC, Paris, France
Copyright Elsevier

A variety of polycyclic aromatic hydrocarbons (PAHs) are reported in carbonaceous chondrites (CCs) and in the interstellar medium (ISM). Although PAHs in CCs are not as large as those detected in the ISM, their carbon isotope composition is interpreted as pinpointing an interstellar origin. In contrast, their hydrogen isotope composition can be related to the extent of secondary processes, as is the proportion of alkylated PAHs within CCs. Here, we experimentally investigate the molecular and isotopic evolution of PAHs under simulated asteroidal hydrothermal conditions at 150 °C. Results show that PAHs are chemically stable under these conditions whatever their size, i.e. no destruction, conjugation nor alkylation occurs, even in the presence of other reactive organic molecules. Plus, PAHs retain their carbon isotope compositions even in the presence of another carbon-rich reservoir, either organic or inorganic. On the other hand, their hydrogen isotope composition is modified through exchange with water. Of note, as shown by additional experiments, the presence of smectites, abundant in CCs, impacts the relative abundances of extractable PAHs, saponite trapping more efficiently the larger PAHs. Altogether, results of the present experiments show that PAHs of CCs can be used as tracers of both pre-accretion and secondary processes.

^1,2D.M. Bower et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115626]
¹University of Maryland, Department of Astronomy, College Park, MD 20742, United States of America
²NASA/Goddard Space Flight Center, Greenbelt, MD 20771, United States of America
Copyright Elsevier

Life detection in the solar system relies on the unambiguous identification of signatures of life and habitability. Organic molecules are essential to life as we know it, and yet many organic compounds are ubiquitous in the solar system and can be synthesized abiotically; thus, their presence alone is not indicative of life. On Earth, chemical signatures of life’s processes are often left behind in minerals through the biologically induced formation of secondary minerals or intermediary organic complexes. In natural rocks biomolecules and organic species often co-occur with minerals, and their overlapping peaks can create difficulties in interpretation. In the process of identifying the minerals and organic species in our basaltic samples we noticed signatures for cyanates co-occurring with organic molecules. Cyanates are an overlooked group of nitrogen compounds in which C is bonded to N (e.g., OCN− or SCN−) that often co-occur with urea and ammonium in environments where microorganisms are present. These compounds are common in many terrestrial and oceanic environments and play an important role in biogeochemical nitrogen cycling. In natural systems, these compounds form as the result of multiple biogeochemical pathways, often from the interaction of microbes with a chemically active environment. These interactions leave behind signatures in the form biotic breakdown products such as urea or ammonium and organic reaction byproducts that are observable with spectroscopic methods. To explore these relationships, we used field-portable Raman spectrometers and laboratory micro-Raman imaging to characterize and compare samples collected from two different terrestrial basaltic environments, a lava tube on Mauna Loa, Hawaii, dominated by the precipitation of sulfate minerals and a geothermal stream at Hveragil, Iceland dominated by the precipitation of carbonate minerals. The Raman (RS) measurements were complemented by laser induced breakdown spectroscopy (LIBS), Long-wave Infrared (IR) LIBS, with the addition of gas chromatograph mass spectrometry (GC–MS) and inductively coupled plasma-mass spectrometry (ICP-MS) to identify cyanate compounds, biomolecules, and other nitrogenous compounds related to the breakdown or production of cyanate in host basalts and secondary precipitates. The RS data suggest that the reason for RS cyanate signatures in the carbonate samples could be due to luminescence artifacts while those detected in the host basalts may be due to hydrolysis chemistry. The cyanate signatures detected in the lava tube samples dominated by sulfates do not seem to be luminescence artifacts but may in fact be evidence of an active microbial nitrogen cycle. Our results inform the spectroscopic detection of cyanates in planetary analog environments and the challenges in their identification. Further work is needed to understand their potential as biosignatures on other planetary bodies.

^1,2E. T. DUNHAM,³A. SHEIKH,³D. OPARA,¹N. MATSUDA,^1,4M.-C. LIU,¹K. D. MCKEEGAN
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.13975]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, California 90025,USA
²Department of Earth and Planetary Science, University of California, Santa Cruz, Santa Cruz, California 95064, USA
³Harvard-MIT Science Research Mentoring Program, Boston, Massachusetts 02142, USA
⁴Lawrence Livermore National Laboratory, Livermore, California 94550, USA
Published by arrangement wit John Wiley & Sons

As the Sun was forming, calcium–aluminum-rich inclusions (CAIs) were the firstrocks to have condensed in the hottest regions of the solar nebula disk. Carbonaceouschondrites (CCs) contain abundant CAIs but are thought to have accreted in the outerSolar System, requiring that CAIs must have been transported outward. Curiously, CAIsare rare in ordinary, enstatite, rumuruti, and kakangari chondrites, non-carbonaceouschondrites (NCs), that likely formed in the inner Solar System. Thus, CAI abundances andcharacteristics can provide constraints on the early dynamical evolution of the disk. In thiswork, we address whether the hypothesis of an early-formed proto-Jupiter “opening a gap”in the disk can explain the dichotomy in the relative abundance of CAIs in CC and NCchondrites. We searched 76 NC meteorite sections to find 232 CAIs which have an averageapparent diameter of 46μm and comprise 0.01 area%, about half the size of and~200 timesless abundant than CC CAIs on average. Unlike CC CAIs, only 4% of the NC CAIscontain melilite and most contain alteration features suggesting that NC CAIs underwentpervasive fluid-assisted thermal metamorphism on asteroidal parent bodies. However, basedon NC CAI populations correlating with meteorite metamorphic grade, we argue that diskdynamics is likely the primary reason behind the existence of small (<100μm) and rare NCCAIs. Our data support astrophysical models which suggest that, after outward transport ofCAIs, formation of a gap in the disk trapped CAIs in the outer Solar System.

¹Steven J. Desch,²Daniel R. Dunlap,³Curtis D. Williams,⁴Prajkta Mane,⁵⁵Emilie T. Dunham
Icarus(in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115611]
¹School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe, 85287-1404, AZ, USA
²Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, 37830, TN, USA
³Earth and Planetary Sciences Department, University of California, Davis, One Shields Ave., Davis, 95616, CA, USA
⁴Lunar and Planetary Institute, USRA, 3600 Bay Area Blvd., Houston, 77058, TX, USA
⁵Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, PO Box 951567, Los Angeles, 90095-1567, CA, USA
Copyright Elsevier

Astrophysical models of planet formation require accurate radiometric dating of meteoritic components by short-lived (Al-Mg, Mn-Cr, Hf-W) and long-lived (Pb-Pb) chronometers, to develop a timeline of such events in the solar nebula as formation of Ca-rich, Al-rich Inclusions (CAIs), chondrules, planetesimals, etc. CAIs formed mostly around a time (“t=0”) when the short-lived radionuclide 26Al (t1/2=0.72 Myr) was present and presumably homogeneously distributed at a known level we define as (26Al/27Al)SS≡5.23×10−5. The time of formation after t=0 of another object can be found by determining its initial (26Al/27Al)0 ratio and comparing it to (26Al/27Al)SS. Dating of meteoritic objects using the Mn-Cr or Hf-W systems is hindered because the abundances (53Mn/55Mn)SS and (182Hf/180Hf)SS at t=0 are not known precisely. To constrain these quantities, we compile literature Al-Mg, Mn-Cr, Hf-W and Pb-Pb data for 14 achondrites and use novel statistical techniques to minimize the discrepancies between their times of formation across these systems. We find that for (53Mn/55Mn)SS=(8.09±0.65)×10−6, (182Hf/180Hf)SS=(10.42±0.25)×10−5, tSS=4568.36±0.20Myr, and a 53Mn half-life of 3.80±0.23 Myr, these four free parameters make concordant 37 out of 38 formation times recorded by the different systems in 14 achondrites. These parameters also make concordant the ages derived for chondrules from CB/CH achondrites, formed simultaneously in an impact, and are apparently concordant with the I-Xe chronometer as well. Our findings provide very strong support for homogeneity of 26Al, 53Mn, and 182Hf in the solar nebula, and our approach offers a framework for more precise chronometry.

¹Steven J. Desch,¹Daniel R. Dunlap,³Emilie T. Dunham,⁴Curtis D. Williams,⁵Prajkta Mane
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115607]
¹School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe, 85287-1404, AZ, USA
²Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, 37830, TN, USA
³Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, PO Box 951567, Los Angeles, 90095-1567, CA, USA
⁴Earth and Planetary Sciences Department, University of California, Davis, One Shields Ave., Davis, 95616, CA, USA
⁵Lunar and Planetary Institute, USRA, 3600 Bay Area Blvd., Houston, 77058, TX, USA
Copyright Elsevier

We use rapidly cooled achondrites to test the assumption of 26Al homogeneity in the solar nebula, by checking if there is a single value of tSS, the absolute “Pb-Pb” age of the Solar System’s t=0, that makes concordant their ages from the Al-Mg and Pb-Pb systems. We find that values tSS=4568.42±0.24 Myr do make these ages concordant, and therefore the hypothesis of homogeneous 26Al is not falsified. This age, defined to be when the solar nebula had (26Al/27Al)=5.23×10−5, is significantly older than the ≈ 4567.3 Myr inferred from direct measurements of Pb-Pb ages in CAIs. Discrepancies between the Al-Mg and Pb-Pb chronometers in chondrules and CAIs have previously been interpreted as arising from heterogeneities in 26Al, under the presumption that the Al-Mg and Pb-Pb systems in CAIs closed simultaneously. We examine this assumption and show that resetting is to be expected in CAIs. In particular, we quantitatively demonstrate that it is plausible that Pb-Pb ages of CAIs were reset at late times, without resetting the earlier Al-Mg ages, if they were transiently heated in the same manner as chondrules. We critically examine Pb-Pb isochrons, refining data and suggesting best practices for their calculation and reporting. We advocate reporting chronometry as times of formation after t=0 rather than absolute ages, as only the former is useful for astrophysical models of the solar nebula. We advocate averaging of multiple samples, rather than anchoring to individual meteorites, to improve precision.