¹Lidia Pittarello,^2,3Akira Yamaguchi,⁴Julia Roszjar,⁵Vinciane Debaille,^1,4Christian Koeberl,⁶Philippe Claeys
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13284]
¹Department of Lithospheric Research, University of Vienna, Althanstraße 14, A‐1090 Vienna, Austria
²National Institute of Polar Research, 10‐3 Midori‐cho, Tachikawa, Tokyo, 190‐8518 Japan
³Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, 190‐8518 Japan
⁴Natural History Museum Vienna, Burgring 7, A‐1010 Vienna, Austria
⁵Laboratoire G‐Time (Géochimie: Traçage isotopique, minéralogique et élémentaire), Université Libre de Bruxelles, Av. F.D., Roosevelt 50, 1050 Brussels, Belgium
⁶Analytical, Environmental and Geo‐Chemistry (AMGC), Vrije Universiteit Brussel, Pleinlaan 2, B‐1050 Brussels, Belgium
Published by arrangement with John Wiley & Sons

Meteorite fusion crusts are quenched melt layers formed during meteoroid atmospheric entry, mostly preserved as coating on the meteorite surface. Antarctic ureilite Asuka (A) 09368 and H chondrites A 09004 and A 09502 exhibit well preserved thick fusion crusts, characterized by extensive olivine crystallization. As olivine is one of the major components of most meteorites and its petrologic behavior is well constrained, it can be roughly considered as representative for the bulk meteorite. Thus, in this work, the evolution of olivine in fusion crusts of the above‐listed selected samples is investigated. The different shape and chemistry of olivine crystallized in the fusion crust, both as overgrown rim on relic olivine clasts and as new crystals, suggest a general temperature and cooling rate gradient. The occurrence of reverse and oscillatory zoning in individual olivine grains within the fusion crust suggests complex redox reactions. Overall, the investigated fusion crusts exhibit a general oxidation of the relatively reduced initial material. However, evidence of local reduction is preserved. Reduction is likely triggered by the presence of carbon in the ureilite or by overheating during the atmospheric entry. Constraining these processes provides a potential analog for interpreting features observed in cosmic spherules and micrometeorites and for calibrating experiments and numerical models on the formation of fusion crusts.

^1,2Danielle N. Simkus,^2,3José C. Aponte,²Jamie E. Elsila,¹Robert W. Hilts,^2,3Hannah L. McLain,¹Christopher D. K. Herd
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13276]
¹Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2R3 Canada
²Solar System Exploration Division, Code 691, NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA
³Department of Chemistry, Catholic University of America, Washington, DC, 20064 USA
Published by arrangement with John Wiley & Sons

The Tagish Lake carbonaceous chondrite exhibits a unique compositional heterogeneity that may be attributed to varying degrees of aqueous alteration within the parent body asteroid. Previous analyses of soluble organic compounds from four Tagish Lake meteorite specimens (TL5b, TL11h, TL11i, TL11v) identified distinct distributions and isotopic compositions that appeared to be linked to their degree of parent body processing (Herd et al. 2011; Glavin et al. 2012; Hilts et al. 2014). In the present study, we build upon these initial observations and evaluate the molecular distribution of amino acids, aldehydes and ketones, monocarboxylic acids, and aliphatic and aromatic hydrocarbons, including compound‐specific δ13C compositions, for three additional Tagish Lake specimens: TL1, TL4, and TL10a. TL1 contains relatively high abundances of soluble organics and appears to be a moderately altered specimen, similar to the previously analyzed TL5b and TL11h lithologies. In contrast, specimens TL4 and TL10a both contain relatively low abundances of all of the soluble organic compound classes measured, similar to TL11i and TL11v. The organic‐depleted composition of TL4 appears to have resulted from a relatively low degree of parent body aqueous alteration. In the case of TL10a, some unusual properties (e.g., the lack of detection of intrinsic monocarboxylic acids and aliphatic and aromatic hydrocarbons) suggest that it has experienced extensive alteration and/or a distinct organic‐depleted alteration history. Collectively, these varying compositions provide valuable new insights into the relationships between asteroidal aqueous alteration and the synthesis and preservation of soluble organic compounds.

^1,2,3M. D. Suttle,^2,3M. J. Genge,⁴T. Salge,⁵M. R. Lee,¹L. Folco,⁴T. Góral,³S. S. Russell,⁶P. Lindgren
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13279]
¹Dipartimento di Scienze della Terra, Università di Pisa, 56126 Pisa, Italy
²Department of Earth Science and Engineering, Imperial College London, South Kensington, London, SW7 2AZ UK
³Mineral and Planetary Sciences, The Natural History Museum, Cromwell Rd, London, SW7 5BD UK
⁴Imaging and Analysis Centre, Core Research Laboratories, The Natural History Museum, Cromwell Rd, London, SW7 5BD UK
⁵School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ UK
⁶Earth Science and Physical Geography, Lund University, 221 00 Lund, Sweden
Published by arrangement with John Wiley & Sons

We report the discovery of a partially altered microchondrule within a fine‐grained micrometeorite. This object is circular, <10 μm in diameter, and has a cryptocrystalline texture, internal zonation, and a thin S‐bearing rim. These features imply a period of post‐accretion parent body aqueous alteration, in which the former glassy igneous texture was subject to hydration and phyllosilicate formation as well as leaching of fluid‐mobile elements. We compare this microchondrule to three microchondrules found in two CM chondrites: Elephant Moraine (EET) 96029 and Murchison. In all instances, their formation appears closely linked to the late stages of chondrule formation, chondrule recycling, and fine‐grained rim accretion. Likewise, they share cryptocrystalline textures and evidence of mild aqueous alteration and thus similar histories. We also investigate the host micrometeorite’s petrology, which includes an unusually Cr‐rich mineralogy, containing both Mn‐chromite spinel and low‐Fe‐Cr‐rich (LICE) anhydrous silicates. Because these two refractory phases cannot form together in a single geochemical reservoir under equilibrium condensation, this micrometeorite’s accretionary history requires a complex timeline with formation via nonequilibrium batch crystallization or accumulation of materials from large radial distances. In contrast, the bulk composition of this micrometeorite and its internal textures are consistent with a hydrated carbonaceous chondrite source. This micrometeorite is interpreted as a fragment of fine‐grained rim material that once surrounded a larger parent chondrule and was derived from a primitive carbonaceous parent body; either a CM chondrite or Jupiter family comet.

¹Ana Černok,^2,3Lee Francis White,⁴James Darling,⁴Joseph Dunlop,^1,5Mahesh Anand
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13278]
¹School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
²Centre for Applied Planetary Mineralogy, Department of Natural History, Royal Ontario Museum, Toronto, ON, M5S 2C6 Canada
³Department of Earth Sciences, University of Toronto, Toronto, ON, M5S 3B1 Canada
⁴School of Earth & Environmental Sciences, University of Portsmouth, Burnaby Road, Portsmouth, PO1 3QL, UK
⁵Department of Earth Sciences, The Natural History Museum, London, SW7 5BD UK
Published by arrangement with John Wiley & Sons

Apatite and merrillite are the most common phosphate minerals in a wide range of planetary materials and are key accessory phases for in situ age dating, as well as for determination of the volatile abundances and their isotopic composition. Although most lunar and meteoritic samples show at least some evidence of impact metamorphism, relatively little is known about how these two phosphates respond to shock‐loading. In this work, we analyzed a set of well‐studied lunar highlands samples (Apollo 17 Mg‐suite rocks 76535, 76335, 72255, 78235, and 78236), in order of displaying increasing shock deformation stages from S1 to S6. We determined the stage of shock deformation of the rock based on existing plagioclase shock‐pressure barometry using optical microscopy, Raman spectroscopy, and SEM‐based panchromatic cathodoluminescence (CL) imaging of plagioclase. We then inspected the microtexture of apatite and merrillite through an integrated study of Raman spectroscopy, SEM‐CL imaging, and electron backscatter diffraction (EBSD). EBSD analyses revealed that microtextures in apatite and merrillite become progressively more complex and deformed with increasing levels of shock‐loading. An early shock‐stage fragmentation at S1 and S2 is followed by subgrain formation from S2 onward, showing consistent decrease in subgrain size with increasing level of deformation (up to S5) and finally granularization of grains caused by recrystallization (S6). Starting with 2°–3° of intragrain crystal‐plastic deformation in both phosphates at the lowest shock stage, apatite undergoes up to 25° and merrillite up to 30° of crystal‐plastic deformation at the highest stage of shock deformation (S5). Merrillite displays lower shock impedance than apatite; hence, it is more deformed at the same level of shock‐loading. We suggest that the microtexture of apatite and merrillite visualized by EBSD can be used to evaluate stages of shock deformation and should be taken into account when interpreting in situ geochemically relevant analyses of the phosphates, e.g., age or volatile content, as it has been shown in other accessory minerals that differently shocked domains can yield significantly different ages.

¹J.Delpeyrat,²F.Pigeonneau,¹G.Libourel
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.03.036]
¹Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
²MINES ParisTech, PSL Research University, CEMEF – Centre de mise en forme des matériaux, CNRS UMR 7635, CS 10207, Rue Claude Daunesse, 06904 Sophia Antipolis Cedex, France
Copyright Elsevier

In an effort to better use thermal histories of chondrules in chondrites to test chondrule formation models, the present note addresses the formation of chondrules through the radiative cooling of a droplet cloud of non-uniform density. More generally, we show that the cooling rates obtained can be related not only to the different types of texture of the chondrules but also to their relative abundance in order to evaluate the relevance of models concerning the formation of chondrules.

Lionel Vacher
PhD Link to the Thesis [http://www.theses.fr/2018LORR0229]
CRPG-CNRS Université de Lorraine 15, Rue Notre Dame des Pauvres 54501 VANDOEUVRE-LÈS-NANCY
Copyright Elsevier

Carbonaceous asteroids were affected by aqueous alteration processes that have strongly modified their primary mineralogy in favour of a wide diversity of newly formed phases. Despite the numerous studies carried out on hydrated chondrites (CM chondrites), the physicochemical conditions of aqueous alteration and the identification of the water sources accreted by asteroids are still poorly constrain. From the mineralogical and isotopic survey of secondary phases, this thesis aims (i) to decipher the origin and evolution of water accreted by primitive asteroids and (ii) to retrace the physicochemical conditions of aqueous alteration using hydrothermal laboratory experiments. First of all, our results show that the pristine CM chondrite Paris contains Ca-carbonates whose O-isotopic compositions ([delta]17,18O) requires an 8-35% contribution of water ice from the outer part of the Solar System. In addition, our C-isotopic analyses conducted on these same Ca-carbonates indicate similar [delta]13C values to those of the soluble organic matter (SOM) that constitute carbonaceous chondrites. Thus, we suggest that SOM is the most probable source of carbon to form Ca-carbonates. Then, the study of different clasts in the CM chondrite Boriskino revealed that this meteorite has experienced high intensity impact events, causing the formation of fractures and the circulation of later 16O-rich fluid flow. Finally, our low temperature laboratory experiments successfully synthetized the most characteristic phases of CM chondrites: tochilinite and cronstedtite. Moreover, by comparing our results to other experimental studies, we observed a positive correlation between the nMg content in the hydroxide layer of synthetic tochilinite and temperature. This correlation suggests that the chemical composition of tochilinite represents as powerful proxy to retrace the alteration temperature experienced by CM chondrites

^1,2Matthew S. Huber,^2,3Christian Koeberl,⁴ Frank C. Smith,⁴Billy P. Glass,⁵Roland Mundil,⁶Iain McDonald
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13271]
¹Department of Geology, University of the Free State, 205 Nelson Mandela Dr., Bloemfontein, South Africa
²Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A‐1090 Vienna, Austria
³Natural History Museum, Burgring 7, A‐1010 Vienna, Austria
⁴Department of Geological Sciences, University of Delaware, Penny Hall, 255 Academy Street, Newark, Delaware, 19716 USA
⁵Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California, 94709 USA
⁶School of Earth and Ocean Sciences, Cardiff University, Park Place, Cardiff, CF10 3AT UK
Published by arrangement with John Wiley & Sons

Samples from a single outcrop of the Graenseso spherule layer, Midternaes, South Greenland, consist of a spherule‐bearing dolomixtite with matrix‐supported intraclasts up to 1 m in size. In addition to field observations, we performed mineralogical and whole rock geochemical analysis, including electron microprobe, neutron activation analysis, X‐ray fluorescence, and mass spectrometry of the horizon and the overlying and underlying strata. We show that the spherules are petrographically similar to those in the Zaonega spherule layer, Karelia, Russia. Our petrographic and chemical results are consistent with the previous suggestion that the Grænsesø layer correlates with the Zaonega layer, and it is possible that both layers are related to the Vredefort impact event. The samples containing spherules, as well as the overlying rocks, have elevated REEs compared to the underlying pre‐impact layer, suggestive of a new continental source of sediment that may be coincident with the impact event. Zircons separated from the lower part of the Grænsesø spherule layer display complex age patterns suggesting that they have genetically different origins based on distinctly different Th/U ratios. Crystallization ages of all groups are ≥ 2.8 Ga, with ~2.8 Ga representing a time of major crustal growth globally. Therefore, we cannot conclusively determine in this study if the zircons are locally derived or if they are transported with the ejecta. The spherule layer was deposited by a high‐energy, subaqueous debris flow, an origin that is consistent with the hypothesis that the layer was deposited by impact‐induced waves and/or currents.

^1,2Juan Luis Rizos,^1,2Julia de León,^1,2Javier Licandro,³Humberto Campins,^1,2,5Marcel Popescu,³Noemí Pinilla-Alonso,⁴Dathon Golish,³Mario de Prá,⁴Dante Lauretta
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.03.007]
¹Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, E-38205 La Laguna, Tenerife, Spain
²Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
³Physics Department, University of Central Florida, P.O. Box 162385, Orlando, FL 32816-2385, USA
⁴Lunar and Planetary Laboratory, University of Arizona, 1415 N. Sixth Ave., Tucson, AZ 85705-0500, USA
⁵Astronomical Institute of the Romanian Academy, 5 Cuţitul de Argint, 040557 Bucharest, Romania
Copyright Elsevier

The OSIRIS-REx asteroid sample-return mission is investigating primitive near-Earth asteroid (101955) Bennu. Thousands of images will be acquired by the MapCam instrument onboard the spacecraft, an imager with four color filters based on the Eight-Color Asteroid Survey (ECAS): b′ (473 nm), v (550 nm), w (698 nm), and x (847 nm). This set of filters will allow identification and characterization of the absorption band centered at 700 nm and associated with hydrated silicates. In this work, we present and validate a spectral clustering methodology for application to the upcoming MapCam images of the surface of Bennu. Our procedure starts with the projection, calibration, and photometric correction of the images. In a second step, we apply a K-means algorithm and we use the Elbow criterion to identify natural clusters. This methodology allows us to find distinct areas with spectral similarities, which are characterized by parameters such as the spectral slope S′ and the center and depth of the 700-nm absorption band, if present. We validate this methodology using images of (1) Ceres from NASA’s Dawn mission. In particular, we analyze the Occator crater and Ahuna Mons. We identify one spectral cluster–located in the outer parts of the Occator crater interior–showing the 700-nm hydration band centered at 698 ± 7 nm and with a depth of 3.4 ± 1.0%. We interpret this finding in the context of the crater’s near-surface geology.

^1,2Haiyang S.Wang,^1,2,3Charles H.Lineweaver,^2,3Trevor R.Ireland
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.03.018]
¹Research School of Astronomy and Astrophysics, The Australian National University, Canberra, ACT 2611, Australia
²Planetary Science Institute, The Australian National University, Canberra, ACT 2611, Australia
³Research School of Earth Sciences, The Australian National University, Canberra, ACT 2601, Australia
Copyright Elsevier

We present new estimates of protosolar elemental abundances based on an improved combination of solar photospheric abundances and CI chondritic abundances. These new estimates indicate CI chondrites and solar abundances are consistent for 60 elements. Our estimate of the protosolar “metallicity” (i.e. mass fraction of metals, Z) is 1.40%, which is consistent with a value of Z that has been decreasing steadily over the past three decades from ∼1.9%. We compare our new protosolar abundances with our recent estimates of bulk Earth composition (normalized to aluminium), thereby quantifying the devolatilization in going from the solar nebula to the formation of the Earth. The quantification yields a linear trend log (f) = α log (TC) + β, where f is the Earth-to-Sun abundance ratio and TC is the 50% condensation temperature of elements. The best fit coefficients are: α = 3.676 ± 0.142 and β =  − 11.556 ± 0.436. The quantification of these parameters constrains models of devolatilization processes. For example, the coefficients α and β determine a critical devolatilization temperature for the Earth TD(E) = 1391 ± 15 K. The terrestrial abundances of elements with TC < TD(E) are depleted compared with solar abundances, whereas the terrestrial abundances of elements with TC > TD(E) are indistinguishable from solar abundances. The abundances of noble gases and hydrogen are depleted more than a prediction based on the extrapolation of the best-fit volatility trend. The terrestrial abundance of Hg (TC = 252 K) appears anomalously high under the assumption that solar and CI chondrite Hg abundances are identical. To resolve this anomaly, we propose that CI chondrites have been depleted in Hg relative to the Sun by a factor of 13 ± 7. We use the best-fit volatility trend to derive the fractional distribution of carbon and oxygen between volatile and refractory components (fvol, fref). For carbon we find (0.91 ± 0.08, 0.09 ± 0.08); for oxygen we find (0.80 ± 0.04, 0.20 ± 0.04). Our preliminary estimate gives CI chondrites a critical devolatilization temperature TD(CI) = 550−100+20 K.

¹Shigeru Wakita,¹Hidenori Genda
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.03.008]
¹Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
Copyright Elsevier

Hydrous minerals are found on the surfaces of asteroids, but their origin is not clear. If their origin is endogenic, the hydrous minerals that were formed in the inner part of a planetesimal (or parent body) should come out on to the surface without dehydration. If their origin is exogenic, the source of hydrous minerals accreting onto asteroids is needed. Collisions in the asteroid belt would be related to both origins because collisions excavate the surface and eject the materials. However, the fate of hydrous minerals in large planetesimals during the collisional process has not been well investigated. Here, we explore planetesimal collisions by using the iSALE-2D code, and investigate the effect of an impact for the target planetesimal containing hydrous minerals. Our numerical results for the fiducial case (5 km/s of the impact velocity) show that hydrous minerals are slightly heated during the collisions. This moderate heating indicates that they can avoid the dehydration reaction and keep their original composition. Some hydrous minerals have larger velocity than the escape velocity of the collision system. This means that hydrous minerals can escape from the planetesimal and support the theory of exogenic origin for the hydrous minerals on asteroids. Meanwhile, the velocity of other hydrous minerals is smaller than the escape velocity of the system. This also indicates the possibility of an endogenic origin for the hydrous minerals on asteroids. Our results suggest that hydrous minerals on asteroids can be provided by planetesimal collisions.