¹Alexander N. Krot,²Patricia M. Doyle,¹Kazuhide Nagashima,¹Elena Dobrică,³Michail I. Petaev
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13709]
¹School of Ocean, Earth Science and Technology, Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, 96822 USA
²International School of Cape Town, 4 Edinburgh Close, Western Cape, Wynberg, 7708 South Africa
³Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, 02138 USA
Published by arrangement with John Wiley & Sons

We report on the mineralogy, petrology, and O-isotope compositions of magnetite and fayalite (Fa90−100) from several metasomatically altered and weakly metamorphosed carbonaceous (Y-81020 [CO3.05], EET 90043 [CO3.1], MAC 88107 [CO3.1-like], and Kaba [oxidized Bali-like CV3.1]) and unequilibrated ordinary chondrites (UOCs; Semarkona [LL3.00], MET 00452 [LL3.05], MET 96503 [LL3.05], EET 910161 [LL3.05], Ngawi [LL3.0−3.6 breccia], and Vicência [LL3.2]). In MAC 88107, EET 90043, and Kaba, nearly pure fayalite (Fa98−100) associates with phyllosilicates, magnetite, Fe,Ni-sulfides, and hedenbergite (Fs~50Wo~50), and occurs in all chondritic components—chondrules, matrices, and refractory inclusions. In UOCs, nearly pure fayalite (Fa95−98) associates with phyllosilicates and magnetite, and occurs mainly in matrices and fine-grained chondrule rims. Oxygen-isotope compositions of fayalite and magnetite in UOCs, COs, CVs, and MAC 88107 are in disequilibrium with those of chondrule olivine and low-Ca pyroxene phenocrysts, and plot along mass-dependent fractionation lines with slope of ~0.5, but different Δ17O (~+4.3 ± 1.4‰, −0.2 ± 0.6‰, −1.5 ± 1‰, and −1.8 ± 0.8‰, respectively). Based on the mineralogical observations, thermodynamic analysis, O-isotope compositions, and recently reported experimental data, we infer that (1) fayalite and magnetite in COs, CVs, MAC 88107, and UOCs resulted from aqueous fluid–rock interaction on the chondrite parent asteroids that occurred at low local water-to-rock mass ratios (0.1−0.4) and elevated temperatures (~100−300 °C), and (2) Δ17O of fayalite and magnetite reflects O-isotope compositions of aqueous fluids on the host meteorite parent bodies. The observed differences in Δ17O of fayalite–magnetite assemblages in UOCs, CVs, COs, and MAC 88107 suggest that water ices that accreted into the ordinary chondrite and carbonaceous chondrite parent asteroids had different Δ17O, implying spatial and/or temporal variations in O-isotope compositions of water in the protoplanetary disk.

¹Nancy L. Chabot,²Bidong Zhang
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13740]
¹Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, Laurel, Maryland, 20723 USA
²Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, California, 90095-1567 USA
Published by arrangement with John Wiley & Sons

As the largest magmatic iron meteorite group, the IIIAB group is often used to investigate the process of core crystallization in asteroid-sized bodies. However, previous IIIAB crystallization models have not succeeded in both explaining the scatter among IIIAB irons around the main crystallization trends and using elemental partitioning behavior consistent with experimental determinations. This study outlines a revised approach for modeling the crystallization of irons that uses experimentally determined partition coefficients and can reproduce the IIIAB trends and their associated scatter for 12 siderophile elements simultaneously. A key advancement of this revised trapped melt model is the inclusion of an effect on the resulting solid metal composition due to the formation of troilite. The revised trapped melt model supports the previous conclusion that trapped melt played an important role in the genesis of IIIAB irons and matches the trace element fractionation trends observed in the Cape York suite as due to different amounts of trapped melt. Applying the revised trapped melt model to 16 elements as well as S and Fe, the bulk composition of the IIIAB core is found to have a composition consistent with that expected from a chondritic precursor for refractory siderophile elements but with evidence for depletions of more volatile elements. The bulk S composition of the IIIAB core is estimated as 9 ± 1 wt%, implying that a substantial amount of S-rich material from the IIIAB core is underrepresented in our meteorite collections. Future applications of the revised trapped melt model to other magmatic iron meteorite groups can enable comparisons between the core compositions and crystallization processes across the early solar system.

¹E.Rondón,¹D.Lazzaro,¹J.Carvano,¹F.Monteiro,¹P.Arcoverde,¹M.Evangelista,¹J.Michimani,¹W.Mesquita,¹T.Rodrigues
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114723]
¹Observatório Nacional, Rua Gal. José Cristino 77, 20921-400, Rio de Janeiro, Brazil
Copyright Elsevier

The observation of objects of the Atiras population is a challenge due to the narrow time-window in which observations are possible and, even so, at very low altitudes. This is due to the orbit of these objects, internal to that of the Earth. In this work we present the results of a photometric observational campaign of Atiras aiming to determine their physical parameters using the rotational light curve, the solar phase curve and the photometric spectrum. The period and amplitude have been determined for the asteroids (163693) Atira, (413563) 2005 TG45 and 2017 YH. In the case of (163693) Atira, we have determined a plausible rotational period , where the composite light curve presents structure usually related to the presence of a companion, as it has been suggested by radar observations of this asteroid. For asteroids (163693) Atira, (413563) 2005 TG45, (481817) 2008 UL90 and 2018 JB3 it was possible to derive the absolute magnitude and the phase coefficient. The obtained values are similar to those observed for asteroids with intermediate to low albedo. Finally, for asteroid (163693) Atira we have obtained a featureless photometric spectrum which is compatible in the Carvano taxonomic scheme with the Xp, Dp or Cp classes. No appreciable surface variations were observed for this object.

¹Thomas M.McCollom,²Frieder Klein,¹Mitchell Ramba
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114754]
¹Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309, USA
²Woods Hole Oceanographic Institution, Wood Hole, MA 02543, USA
Copyright Elsevier

Serpentinization of olivine-rich ultramafic rocks is increasingly recognized to have been widespread in the solar system throughout its history. This process has gained particular attention among planetary scientists because it generates molecular hydrogen (H2) and methane (CH4), compounds that can supply metabolic energy to biological communities and contribute to greenhouse warming of planetary atmospheres. While serpentinization of olivine has been the subject of numerous experimental and theoretical studies over the years, this work has focused almost exclusively on the magnesium-rich olivine that is characteristic of the terrestrial mantle. In contrast, very few studies have examined serpentinization of the more iron-enriched olivine compositions that may be more common in other rocky planetary bodies in the solar system. Accordingly, a series of thermodynamic models were constructed to investigate secondary mineral formation and H2 generation during serpentinization of olivine as a function of Fe content and temperature. The results show that serpentinization of Fe-rich olivine is capable of generating substantially greater amounts of H2 per mole than is observed for serpentinization of Mg-rich olivine, by a factor of two to ten depending on temperature and olivine composition. For all olivine compositions, H2 is generated from ferric Fe incorporated into both magnetite and serpentine at higher temperatures; however, it is derived exclusively from precipitation of serpentine at lower temperatures as brucite replaces magnetite in the equilibrium secondary mineral assemblage. Serpentine and brucite formed during serpentinization are predicted to become increasingly enriched in Fe with greater Fe content of the original olivine, although the serpentine has proportionally lower Fe contents than the olivine while brucite has somewhat higher Fe contents. Between 10% and 40% of the Fe partitioned into serpentine occurs in the ferric state (FeIII), which accounts for a substantial fraction of H2 production for most conditions. In addition, the maximum temperature at which olivine undergoes serpentinization decreases with increasing Fe content of the olivine, so that Fe-enriched olivine can remain stable to lower temperatures when compared with more Mg-rich olivine compositions. Overall, the results indicate that serpentinization on other planetary bodies may have a substantially greater capacity to supply H2 to support biological communities and enhance atmospheric greenhouse warming than analogous processes on Earth.

¹Fridolin Spitzer,¹Christoph Burkhardt,¹Jonas Pape,¹Thorsten Kleine
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13744]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
Published by arrangement with John Wiley & Sons

The ungrouped iron meteorite Nedagolla is the first meteorite with bulk Mo, Ru, and Ni isotopic compositions that are intermediate between those of the noncarbonaceous (NC) and carbonaceous (CC) meteorite reservoirs. The Hf-W chronology of Nedagolla indicates that this mixed NC–CC isotopic composition was established relatively late, more than 7 Myr after solar system formation. The mixed NC–CC isotopic composition is consistent with the chemical composition of Nedagolla, which combines signatures of metal segregation under more oxidizing conditions (relative depletions in Mo and W), characteristic for CC bodies, and more reducing conditions (high Si and Cr contents), characteristic for some NC bodies, in a single sample. These data combined suggest that Nedagolla formed as the result of collisional mixing of NC and CC core material, which partially re-equilibrated with silicate mantle material that predominantly derives from the NC body. These mixing processes might have occurred during a hit-and-run collision between two differentiated bodies, which also provides a possible pathway for Nedagolla’s extreme volatile element depletion. As such, Nedagolla provides the first isotopic evidence for early collisional mixing of NC and CC bodies that is expected as a result of Jupiter’s growth.

¹Joseph I. Goldstein,²Edward R. D. Scott,¹Timothy B. Winfield,^3,4Jijin Yang
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13745]
¹Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, Massachusetts, 01003 USA
²Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i, 96822 USA
³Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
⁴College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049 China
Published by arrangement with John Wiley & Sons

Metallographic cooling rates of 10–20 K Myr−1 were obtained for four IAB iron meteorites from electron probe analyses of taenite and models simulating kamacite growth. Cooling rates were also determined for 21 irons in the IAB complex from the size of tetrataenite particles in the cloudy zone and a calibration curve using data for the four IAB irons and five other iron and stony iron groups. We find that the closely related IAB main group, low-Au subgroups, Pitts grouplet irons, and San Cristobal cooled through 500 °C at 10–35 K Myr−1. The ungrouped IAB complex irons, Santa Catharina and Twin City, have bulk Ni contents of ~30 wt% and cooled much faster at ~200–1000 K Myr−1, most probably in a different parent body. Our cooling rates and observations allow conflicting interpretations of the nature of the low-Ni phase in the cloudy zone to be reconciled. We infer that in fast cooled irons like Santa Catharina, the low-Ni phase transforms to antitaenite, but in very slowly cooled meteorites like mesosiderites, martensite forms instead. In meteorites with intermediate cooling rates like IAB irons, the bulk of the cloudy zone probably contains antitaenite as the low-Ni phase, but in the coarse region next to tetrataenite, martensite is present. Published isotopic ages show that metal–silicate mixing in group IAB irons occurred ~5–10 Myr after CAI formation, but the nature and timing of the impact are poorly constrained at present. Ar-Ar ages testify to shock reheating of plagioclase during cooling over ~100 Myr. However, the cloudy zone is well preserved showing that metal was not heated significantly by shocks after slow cooling through 400 °C.

¹Lingzhi Sun,¹Paul Lucey,²Casey I.Honniball,¹Macey Sandford,¹Emily S.Costello,¹Liliane Burkhard,³Reilly Brennan,¹Chiara Ferrari-Wong
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114740]
¹Hawai‘i Institute of Geophysics and Planetology, Department of Earth Sciences, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
²NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
³Georgia Institute of Technology, Atlanta, GA 30332, USA
Copyright Elsevier

The reflected light from the lunar surface is polarized and contains perpendicular () and parallel () branches. To provide supporting data for the first polarimetric camera (PolCam) on board the Korean Pathfinder lunar orbiter, in this work, we built a polarimeter and measured the polarized spectra for eight Apollo soils that span a wide range in composition and maturity. We found a linear correlation between reflectance R and the difference of perpendicular and parallel branches: , and b’ might be sensitive to the grain size of lunar soils. The regression coefficient b’ can be derived from both positive and negative polarization spectra and has little dependence on wavelength, thus it has great potential in estimating grain size for lunar soils. We also used radiative transfer equations to calculate the real index of optical constants and to reproduce the perpendicular and parallel polarized spectra for the lunar soils. We correlated polarimetry indexes including polarization degree () and the difference of the perpendicular and parallel branches () with the abundances of FeO and TiO2 and soil maturity, and our result indicates that these two polarimetry indexes show dependence on both the compositions and soil maturity.

^1,2Vardan Adibekyan et al. (>10)
Science 374, 330-332 Link to Article [DOI: 10.1126/science.abg8794]
¹Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Centro de Astrofísica da Universidade do Porto, 4150-762 Porto, Portugal.
²Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal.
Reprinted with permission from AAAS

Stars and planets both form by accreting material from a surrounding disk. Because they grow from the same material, theory predicts that there should be a relationship between their compositions. In this study, we search for a compositional link between rocky exoplanets and their host stars. We estimate the iron-mass fraction of rocky exoplanets from their masses and radii and compare it with the compositions of their host stars, which we assume reflect the compositions of the protoplanetary disks. We find a correlation (but not a 1:1 relationship) between these two quantities, with a slope of >4, which we interpret as being attributable to planet formation processes. Super-Earths and super-Mercuries appear to be distinct populations with differing compositions, implying differences in their formation processes.

¹J.D.Tarnas et al. (>10)
Journal of Geophysical Research (Planets) (In Press) Link to Article [https://doi.org/10.1029/2021JE006898]
¹NASA Jet Propulsion Laboratory, California Institute of Technology
Publishe by Arrangement with John Wiley & Sons

Carbonate minerals have been detected in Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, and within the regional olivine-bearing (ROB) unit in the Nili Fossae region surrounding this crater. It has been suggested that some carbonates in the margin fractured unit, a rock unit within Jezero crater, formed in a fluviolacustrine environment, which would be conducive to preservation of biosignatures from paleolake-inhabiting lifeforms. Here we show that carbonate-bearing rocks within and outside of Jezero crater have the same range of visible-to-near-infrared carbonate absorption strengths, carbonate absorption band positions, thermal inertias, and morphologies. Thicknesses of exposed carbonate-bearing rock cross-sections in Jezero crater are ∼75-90 meters thicker than typical ROB unit cross-sections in the Nili Fossae region, but have similar thicknesses as ROB unit exposures in Libya Montes. These similarities in carbonate properties inside and outside of Jezero crater is consistent with a shared origin for all of the carbonates in the Nili Fossae region. Carbonate absorption minima positions indicate that both Mg- and more Fe-rich carbonates are present in the Nili Fossae region, consistent with the expected products of olivine carbonation. These estimated carbonate chemistries are similar to those in martian meteorites and the Comanche carbonates investigated by the Spirit rover in Columbia Hills. Our results indicate that hydrothermal alteration is the most likely formation mechanism for non-deltaic carbonates within and outside of Jezero crater.

¹Naoma McCall,^1,2Sean P.S.Gulick,³Brendon Hall,^4.5Auriol S.P.Rae,⁴Michael H.Poelchau,⁶Ulrich Riller,⁷Johanna Lofi,⁸Joanna V.Morgan
Earth and Planetary Science Letters 576, 117236 Link to Article [https://doi.org/10.1016/j.epsl.2021.117236]
¹University of Texas at Austin, Jackson School of Geosciences, Institute for Geophysics & Department of Geological Sciences, J.J. Pickle Research Campus, Austin, TX 78758, USA
²Center for Planetary Systems Habitability, University of Texas at Austin, Austin, TX, USA
³Enthought, Inc., Austin, TX, USA
⁴Institute of Earth and Environmental Sciences—Geology, Albert-Ludwigs Universität Freiburg, Albertstrasse 23b, Freiburg 79110, Germany
⁵Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
⁶Institut für Geologie, Universität Hamburg, Bundesstrasse 55, Hamburg, 20146, Germany
⁷Géosciences Montpellier, Université de Montpellier, CNRS, France
⁸Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK
Copyright Elsevier

Hypervelocity impact cratering is an important geologic process but the rarity of large terrestrial impact craters on Earth and the limited technical options to study cratering processes in the laboratory hinders our understanding of large-scale impact processes. Drill core recovered from the peak ring of the Chicxulub impact crater during International Ocean Discovery Program (IODP)/International Continental scientific Drilling Program (ICDP) Expedition 364 provides an opportunity to examine target rock deformation and thus, to assess cratering models in this regard. Using oriented computer tomography (CT) scans and line scan images of the core, we present the orientations of mm-to-cm-scale planar cataclasite and ultracataclasite zones in the deformed granitoid target rock of the peak ring. In the upper 470 m of the target rock, the cataclasite zones dip towards the crater center, whereas the dip directions for the ultracataclasite zones are approximately tangential to the peak ring. These two orientations are consistent with deformation expected from hydrocode-modeled principal stress directions for the outward movement of rocks as the transient crater develops, and the inward movement of rocks associated with collapse of the transient crater. Near the base of the core is a 96 m-thick interval of highly-deformed target rock with impact melt rock and rock fragments not observed elsewhere in the core; this interval has previously been interpreted as an imbricate thrust zone within the peak ring. The cataclasite zones below this thrust zone have different orientations than those in the 470 m-thick block above. This observation implies a differential rotation from the overlying block during the final stages of peak-ring formation. Our results support an acoustic fluidization process, wherein blocks that vibrate or slide relative to each other allow the target rock to flow during transient crater collapse, and that the size of coherent rock blocks increases over the course of crater modification as the target rock regains its cohesive strength and acoustic fluidization decreases.