¹Trygve Prestgard,¹Lydie Bonal,¹Jolantha Eschrig,²Jérôme Gattacceca,²Corinne Sonzogni,¹Pierre Beck
Meteorics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13736]
¹Institut de Planétologie et d’Astrophysique de Grenoble, Université Grenoble Alpes, CNRS CNES, 38000 Grenoble, France
²CNRS, Aix Marseille Univ, IRD, Coll France, INRA, CEREGE, Aix-en-Provence, France
Published by arrangement with John Wiley & Sons

Miller Range (MIL) 07687 is a peculiar carbonaceous chondrite officially classified as a CO3. However, it has been found to display unique petrographic properties that are atypical of this group. Moreover, Raman spectra of its polyaromatic carbonaceous matter do not reflect a structural order consistent with the metamorphic history of a type 3 chondrite. As a result, it has been suggested to be an ungrouped C2 chondrite with CO affinities, although it has not been fully excluded as a CO chondrite. The ambiguity of the meteorite’s classification is the motivation behind the present study. We conclude that MIL 07687 is a unique carbonaceous chondrite with possible affinities to CO, CM, and/or some ungrouped carbonaceous chondrites. The difficulty in classifying this meteorite stems from (1) its heavily weathered nature, which interferes with the interpretation of our oxygen (O-)isotopic measurements; (2) the overlap in the petrographic and O-isotopic descriptions of various COs, CMs, and ungrouped meteorites in the Meteoritical Society Database. Optical and infrared spectra are consistent with the meteorite’s unequilibrated nature and indicate that it is probably mildly aqueously altered. Despite traces of aqueous alteration having previously been described in MIL 07687, this is the first time that the presence of hydrated amorphous silicates is reported. In fact, our results show that its present hydration is beyond that of most CO3s, less than most CM2s, and comparable to primitive CR2s. Consequently, we support the meteorite’s C2-ung label, although a CO2 or CM2 classification cannot be fully excluded.

^1,2Elisabeth Losa-Adams,^1,3Carolina Gil-Lozano,^4,5Alberto G. Fairén,^6,7Janice L. Bishop,⁷Elizabeth B. Rampe,¹Luis Gago-Duport
Nature Astronomy 5, 936–942 Link to Article [DOI https://doi.org/10.1038/s41550-021-01397-x]
¹Departamento de Geociencias Marinas, Universidade de Vigo, Lagoas-Marcosende, Vigo, Spain
²Centro de Investigación Mariña da Universidade de Vigo (CIM-UVIGO), Vigo, Spain
³Laboratoire de Planétologie et Géodynamique de Nantes (LPGN), CNRS/Université de Nantes, Nantes, France
⁴Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, Madrid, Spain
⁵Department of Astronomy, Cornell University, Ithaca, NY, USA
⁶SETI Institute, Mountain View, CA, USA
⁷NASA Ames Research Center, Moffett Field, CA, USA

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^1,2Nian Wang,^3,4Guiqin Wang,^1,2Ting Zhang,¹Lixin Gu,¹Chi Zhang,¹Sen Hu,⁵Bingkui Miao,^1,2Yangting Lin
Journal of Geophysical Research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2021JE006847]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
²University of Chinese Academy of Sciences, Beijing, 100049 China
³State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640 China
⁴CAS Center for Excellence in Comparative Planetology, China
⁵Key Laboratory of Geological Engineering Center of Guangxi Province, Guilin University of Technology, Guilin, 541004 China
Published by arrangement with John Wiley & Sons

The Huoyanshan iron meteorite shower, recently found in the Gobi Desert of Hami, Xinjiang, China, has very high Ni (21.1 wt%) content and low Au (2.0 ppm), Ir (0.02 ppm), Ge (1.7 ppm), and Ga (1.1 ppm) contents, and was classified into IAB-sLH subgroup. The iron has a finest octahedrite structure of Widmanstätten pattern (the intergrowth of kamacite (α) and taenite (γ)) with plessite matrix, and euhedral schreibersite (Sch) crystals exclusively enclosed in kamacite bands. The textural features suggest the following formation process: γ→γ + Sch →γ+ Sch + α, and then γ→α2 + γ. The metallographic cooling rate of Huoyanshan iron was determined to be 3–50 °C/Myr using both the taenite Ni profile-matching and taenite central Ni content methods, with the bandwidths corrected for crystallographic orientation by electron backscatter diffraction (EBSD). The cooling rate of Huoyanshan is consistent with other sLH and confirms the slow cooling history of the IAB low-Au subgroups. The slow cooling rates of non-magmatic irons required immediate re-accretion with a thick brecciated fragments layer in the parent body after the impact melting event. The depleted but unfractionated Re, Os, Ir, Ru, and Pt and the enriched Pd and Au abundances of Huoyanshan iron and other sLH subgroup show complementary feature to that of refractory metal nuggets in Ca-, Al-rich inclusions (CAIs), which could be explained by extracting the metallic Fe-Ni with HSE predominantly remained in CAIs from a CAI-bearing asteroid. The very high Ni content of sLH subgroup suggests a highly oxidized parental asteroid, but non-carbonaceous chondrite based on Mo isotopic compositions (Worsham et al., 2017). We propose that the Huoyanshan iron and other sLH subgroup were produced by impact melting of a LL like and CAI-bearing asteroid, followed by fast burying of thick and porous silicate breccia.

¹David W. Mittlefehldt et al. (>10)
Journal of Geophysical Research (Planets)(In Press) Link to Article [https://doi.org/10.1029/2021JE006915]
¹Mail code XI3, Astromaterials Research Office, NASA/Johnson Space Center, Houston, Texas, 77058 USA
Published by arrangement with John Wiley & Sons

We have used Mars Exploration Rover Opportunity data to investigate the origin and alteration of lithic types along the western rim of Noachian-aged Endeavour crater on Meridiani Planum. Two geologic units are identified along the rim: the Shoemaker and Matijevic formations. The Shoemaker formation consists of two types of polymict impact breccia: clast-rich with coarser clasts in upper units; clast-poor with smaller clasts in lower units. Comparisons terrestrial craters show that the lower units represent more distal ejecta from at least two earlier impacts, and the upper units are proximal ejecta from Endeavour crater. Both are mixtures of target rocks of basaltic composition with subtle compositional variations caused by differences in post-impact alteration. The Matijevic formation and lower Shoemaker units represent pre-Endeavour geology, which we equate with the regional Noachian subdued cratered unit. An alteration style unique to these rocks is formation of smectite and Si- and Al-rich vein-like structures crosscutting outcrops. Post-Endeavour alteration is dominated by sulfate formation. Rim-crossing fracture zones include regions of alteration that produced Mg-sulfates as a dominant phase, plausibly closely associated in time with the Endeavour impact. Calcium-sulfate vein formation occurred over extended time, including before the Endeavour impact and after the Endeavour rim had been substantially degraded, likely after deposition of the Burns formation that surrounds and embays the rim. Differences in Mg, Ca and Cl concentrations on rock surfaces and interiors indicate mobilization of salts by transient water that has occurred recently and may be ongoing.

¹Henning Dypvik et al. (>10)
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2021.105339]
¹Department of Geosciences and Department of Technology Systems, Univ. of Oslo, P.O. Box 1047, Blindern, NO 0316, Oslo, Norway

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¹Ed Cloutis et al. (>10)
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2021.105336]
¹Department of Geography, 515 Portage Avenue, University of Winnipeg, Winnipeg, MB, R3B 2E9, Canada

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¹Giuliano Kraettli,¹Max W.Schmidt,¹Christian Liebske
Icarus (in Press) link to Article [https://doi.org/10.1016/j.icarus.2021.114699]
¹Department of Earth Sciences, ETH, 8092 Zurich, Switzerland
Copyright Elsevier

In the wake of its accretion, the Moon was likely partially or fully molten, forming a lunar magma ocean (LMO). A fully molten Moon may crystallize neutrally buoyant olivine, whose accumulation may form a barrier leading to a separation into two independently evolving melt reservoirs. This study investigates the crystallization of such a putative basal lunar magma ocean, ranging from the core mantle boundary (with radius r = 380 km) to the level of neutral olivine buoyancy (r = 600 km). Consecutive crystallization experiments determine liquidus temperatures and crystallize 10–30 wt% minerals, before conceptually segregating these according to their buoyancy, and then stepping to a new bulk composition that corresponds to the residual melt after removal of the cumulate minerals.

The first olivine to crystallize from a Taylor Whole Moon composition (twm, XMg = Mg/(Mg + Fe2+) = 0.83) has XMg = 0.94 and is neutrally buoyant at 3.8 GPa according to the melt density model of Lange and Carmichael (1990). Crystallization begins at the core mantle boundary, but early olivine floats and re-dissolves until the magma ocean cools to the liquidus temperature at the depth of neutral buoyancy (1850 °C). At this point a > 500 km thick olivine-only layer could form, mainly fed from the upper magma shell. The crystallization sequence in the basal magma ocean is olivine-only at 1850–1675 °C, 0–26 pcs (wt% percent solidified) → olivine + opx (to 1600 °C, 42 pcs) → opx + cpx + garnet (to 1580 °C, 60 pcs) → cpx + garnet (to 1520 °C, 73 pcs) → cpx + garnet + olivine leaving 11 wt% residual melt at 1450 °C.

Cooling this last melt to 1300 °C leads to 80% garnet + cpx + olivine + Ti-spinel, the residual liquid corresponding to 2.2% of the basal magma ocean. Olivine, opx and cpx remain buoyant over the entire crystallization interval and various pyroxenite layers are added to the olivine layer. Garnet and the final cotectic cpx + garnet + olivine + FeTi-oxide assemblage instead form a 70 km thick basal layer on the core-mantle boundary. Such a layer provides a gravitationally stable high-density lowermost lunar mantle, which would concur with a recent re-analysis of the lunar seismic data. The lowest temperature experiment at 1300 °C, not much above the 1250 °C proposed for the core-mantle boundary from inversion of geophysical data, had about 20% of a highly evolved, dense Fe-rich melt. It is feasible that this melt has remained in its liquid state to present day, providing an explanation for the proposed low vp and vs layer and high dissipation just above the core-mantle boundary.

¹Željko Ivezić,²Vedrana Ivezić,¹Joachim Moeyens,³Carey M.Lisse,⁴Schelte J.Bus,¹Lynne Jones,⁵Brendan P.Crill,^5,6Olivier Doré,⁷Joshua P.Emery
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114696]
¹Department of Astronomy and the DiRAC Institute, University of Washington, 3910 15th Avenue, NE, Seattle, WA 98195, USA
²Department of Computer Science, Princeton University, 35 Olden St, Princeton, NJ 08540, USA
³JHU-APL, SES/SRE, Bldg 200/E206, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
⁴Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822 USA
⁵Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove, Pasadena, CA 91109, USA
⁶California Institute of Technology, Pasadena, CA 91125, USA
⁷Department of Astronomy and Planetary Science, Northern Arizona University, 527 S Beaver Street, Flagstaff, AZ 86011, USA
Copyright Elsevier

We describe the construction and analysis of simulated SPHEREx spectra of Main Belt and Trojan asteroids. SPHEREx will deliver the first all-sky spectral survey at 96 spectral channels between 0.75 m and 5.0 m. We have developed a method for correcting SPHEREx asteroid spectra for intrinsic rotational variability that does not require light curves and can enable studies before LSST light curves become available for this purpose. Using these spectra, we predict that SPHEREx will deliver meaningful flux measurements for about 100,000 asteroids, including close to 10,000 objects with high-quality spectra; this dataset will represent an increase over our current sample size by more than an order of magnitude. The main SPHEREx contribution to asteroid science will be derived from taxonomic classifications, detailed spectroscopic analyses involving a number of diagnostic spectral features associated with olivine, pyroxene, hydroxyl, water ice, and organics, and constraints on thermal properties. We argue that all asteroids with currently known orbits, about a million objects, should be included in the SPHEREx forced photometry object list to maximize its science impact. Our tools and the library of simulated spectra are made publicly available.

¹D.Takir,²M.Matsuoka,³A.Waiters,³H.Kaluna,²T.Usui
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114691]
¹Jacobs, NASA Johnson Space Center, Houston, TX 77058, USA
²Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan
³Physics and Astronomy, University of Hawai’i at Hilo, HI 96720, USA
Copyright Elsevier

We measured near-infrared (NIR) reflectance spectra of Phobos and Deimos, using the prism (0.7–2.52 μm) and long-wavelength cross dispersed (LXD: 1.9–4.2 μm) modes of NASA Infrared Telescope Facility (IRTF)’s SpeX instrument. The goal of this study is to investigate the surface composition of Phobos and Deimos and search for any mineralogical absorption signatures that may be present on their surfaces, especially in the LXD spectral range. Prism spectra of Phobos showed significant slope variation at shorter wavelengths (λ < 1.3 μm), which indicates surface heterogeneity possibly due to regolith’s composition and grain size, and/or space weathering. Deimos’ prism spectra were found to be consistent with the more red-sloped prism spectra of Phobos. The measured LXD spectra of Deimos revealed evidence of hydration with 3-μm band depths at 2.90 μm of 4–5%. The 3-μm band in Deimos could be attributed to exogenic sources such as solar wind implantation or OH-bearing impactors, or to an endogenic source and the presence of carbonaceous material on its surface. Phobos’ and Deimos’ prism and LXD spectra, however, show no indications for absorption signatures of mafic silicates (i.e., pyroxene, olivine), organics nor carbonates.

¹Christian Potiszil,¹Wren Montgomery,¹Mark A.Sephton
Earth and Planetary Science Letters 574, 117149 Link to Article [https://doi.org/10.1016/j.epsl.2021.117149]
¹Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, United Kingdom
Copyright Elsevier

CM2 chondrites experienced widespread aqueous and short term thermal alteration on their parent bodies. Whilst previous Raman spectroscopic investigations have investigated insoluble organic matter (IOM), they have not taken into account the binary nature of IOM. Studies employing mass spectrometry have indicated that IOM also known as macromolecular organic matter (MOM) is in fact composed of two distinct fractions: labile organic matter (LOM) and refractory organic matter (ROM). The ROM component represents the aromatic rich and heteroatom poor component of IOM/MOM, whilst the LOM fraction represents a more heteroatom and aliphatic rich component. Here we report Raman 2D maps and spectroscopic data for Murchison and Mighei, both before and after chemical degradation, which attacks and liberates LOM. The removal of LOM simulates the effects of aqueous alteration, where ester and ether bonds are broken and is thought to release some components to the soluble organic matter (SOM) fraction, also known as the free organic matter fraction (FOM). Raman spectroscopy can be used to reveal the nature of bonding (sp2 and sp3) within carbonaceous materials such as meteoritic organic matter, through evaluation of the D and G band peak centres and FWHM values from the recorded data. The presence of sp3 orbitals indicates that the organic materials contain aliphatic linkages and/or heteroatoms. Statistical analysis of the Raman parameters obtained here indicates that the organic matter originating the Raman response is indistinguishable between the bulk (chemically untreated) and chemically degraded (treated with KOH and HI) samples. Such an observation indicates that the ROM fraction is the major contributor to the Raman response of meteoritic organic matter and thus Raman spectroscopy is unlikely to record any aqueous alteration processes that have affected meteoritic organic matter. Therefore, studies which use Raman to probe the IOM are investigating just one of the components of IOM and not the entire fraction. Studies that aim to investigate the effects of aqueous alteration on meteoritic organic matter should use alternate techniques to Raman spectroscopy. Furthermore, the indistinguishable nature of the Raman response of ROM from Murchison and Mighei suggests these meteorites inherited a ROM component that is chemically similar, reflecting either a common process for the formation of CM2 meteoritic ROM and/or that these meteorites probed the same ROM reservoir.