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.

¹M. V. GORYUNOV,²G. VARGA,²Z. DANKHAZI,³I. FELNER,¹A. V. CHUKIN,⁴E. KUZMANN,⁴Z. HOMONNAY,¹V. I. GROKHOVSKY,¹M. I. OSHTRAKH
Meteoritics & Planetary Science (in Press) Link to Article [doi: 10.1111/maps.13984]
¹Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russian Federation
²Department of Materials Physics, Eotvos Lorand University, Budapest, Hungary
³Racah Institute of Physics, The Hebrew University, Jerusalem, Israel
⁴Laboratory of Nuclear Chemistry, Institute of Chemistry, Eotvos Lorand University, Budapest, Hungary
Published by arrangement with John Wiley & Sons

Gibeon IVA iron meteorite fragment was characterized using optical microscopy,scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-raydiffraction (XRD), magnetization measurements, and M€ossbauer spectroscopy. Opticalmicroscopy and SEM made on the polished section of the meteorite, show the presence ofa-Fe(Ni, Co) andc-Fe(Ni, Co) phases and plessite structures. There are no troilite inclusionsobserved in the studied section. EDS studies indicate some variations in the Ni concentrations:(i) within thea-Fe(Ni, Co) phase in the range~5.00.1–~7.50.1 at% and (ii) within thec-Fe(Ni, Co) phase in the range~26.00.2–~36.10.2 at%. The latter Ni concentrationrange indicates the presence of small amount of the paramagneticc-phase in addition to theferromagneticc-phase. EDS also shows that Ni content in two plessite structures is varying inthe range~16–37 at%, which can indicate the presence of only thea2-Fe(Ni, Co) andc-Fe(Ni,Co) phases in the duplex plessite structure. This may be a result of thec-phase decompositionwith the incomplete martensitic transformation:c?a2+cdue to a faster cooling rate. XRDindicates the presence of~1.3 wt% of thec-Fe(Ni, Co) phase in Gibeon VIA. The saturationmagnetization moment of 185(2) emu g1obtained also confirms the presence of phases withlow and high Ni concentrations. The most appropriate fit of the Gibeon IVA M€ossbauerspectrum demonstrates the presence of five magnetic sextets and one paramagnetic singlet whichare assigned to the ferromagnetica2-Fe(Ni, Co),a-Fe(Ni, Co),c-Fe(Ni, Co), and paramagneticc-Fe(Ni, Co) phases. The relative average Fe contents in these phases are: 13.4% in thea2-Fe(Ni, Co) phase, 78.3% in thea-Fe(Ni, Co) phase, and 8.3% in the ferromagnetic andparamagneticc-Fe(Ni, Co) phases.

^1,2,3,4Sarah McMullan et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.13977]
¹Impact and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, SW7 2BP London, UK
²UK Fireball Network (UKFN), UK
³UK Fireball Alliance (UKFAll), UK
⁴Global Fireball Observatory (GFO), Australia
Published by arrangement with John Wiley & Sons

On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball’s atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s−1). A near-catastrophic fragmentation at ∼0.07 MPa points to the body’s fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures.

^1,2Aryavart ANAND,³Anuj Kumar SINGH,¹Klaus MEZGER,^3.4Jayanta Kumar PATI
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.139821Ó2023]
¹Institut für Geologie, Universität Bern, Bern, Switzerland
²Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
³Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Prayagraj, India
⁴National Centre of Experimental Mineralogy and Petrology, University of Allahabad, Prayagraj, India
Published by arrangement with John Wiley & Sons

The Dhala structure in north-central India is a confirmed complex impactstructure of Paleoproterozoic age. The presence of an extraterrestrial component inimpactites from the Dhala structure was recognized by geochemical analyses of highlysiderophile elements and Os isotopic compositions; however, the impactor type hasremained unidentified. This study uses Cr isotope systematics to identify the type ofprojectile involved in the formation of the Dhala structure. Unlike the composition ofsiderophile elements (e.g., Ni, Cr, Co, and platinum group elements) and their inter-elementratios that may get compromised due to the extreme energy generated during an impact, Crisotopes retain the distinct composition of the impactor. The distincte54Cr value of0.310.09 for a Dhala impact melt breccia sample (D6-57) indicates inheritance from animpactor originating within the non-carbonaceous reservoir, that is, the inner Solar System.Based on the Ni/Cr ratio, Os abundance, and Cr isotopic composition of the samples, theimpactor is constrained to be of ureilite type. Binary mixing calculations also indicatecontamination of the target rock by 0.1–0.3 wt% of material from a ureilite-like impactor.Together with the previously identified impactors that formed El’gygytgyn, Zhamanshin,and Lonar impact structures, the Cr isotopic compositions of the Dhala impactites arguefor a much more diverse source of the objects that collided with the Earth over itsgeological history than has been supposed previously.