^1,2Zelia Dionnet,^3,4,5Martin D. Suttle,^1,2Andrea Longobardo,^1,2Alessandra Rotundi,^3,4Luigi Folco,²Vincenzo Della Corte,⁶Andrew King
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13533]
¹Università di Napoli “Parthenope,” DIST, Centro Direzionale Isola C4, I‐80143 Naples, Italy
²INAF‐IAPS, via Fosso del Cavaliere 100, I‐00133 Rome, Italy
³Dipartimento di Scienze della Terra, Università di Pisa, V. S. Maria 53, I‐56126 Pisa, Italy
⁴Planetary Materials Group, Department of Earth Science, The Natural History Museum, Cromwell Rd, London, SW7 5BD UK
⁵Centro per l’Integrazione della Strumentazione dell’, Università di Pisa, Pisa, Italy
⁶PSICHE Beamline, Synchrotron SOLEIL, Gif‐Sur‐Yvette, France
Published by arrangement with John Wiley & Sons

Giant micrometeorites (MMs; 400–2000 µm) are exceedingly rare and scientifically valuable. Three‐dimensional nondestructive characterization by X‐ray computed tomography (X‐CT) provides information on the petrography and thus petrogenesis of MMs and serves as a guide to maximize subsequent multi‐analytical studies on such precious planetary materials. Here, we discuss the results obtained by X‐CT on 22 giant MMs and the classification based on their 3‐D density contrast images. Scoriaceous and unmelted MMs have distinct porosity ranges (10–40 vol% versus 0–25 vol%, respectively). We observe a porosity variation inside scoriaceous MMs, which allows their atmospheric entry flight history to be resolved. For the first time, spinning entry is explicitly demonstrated for four partially melted MMs. Furthermore, we are able to resolve the thermal gradient in a single particle, based on porosity variation (seen as a progressive increase in pore abundance and size with higher peak temperatures). Moreover, we explore parent body alteration through the 3‐D analysis of pores distribution, showing that shock fabrics are either absent or weakly developed in our data set. Finally, owing to the detection of pseudomorphic chondrules, we estimate that the intensively aqueously altered C1 or CI‐like material could represent 18% of the MM flux at this size fraction (400–1000 µm).

¹Christian Vollmer,¹Mandy Pelka,²Jan Leitner,³Arne Janssen
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13526]
¹Institut für Mineralogie, Westfälische Wilhelms‐Universität, Corrensstr. 24, 48149 Münster, Germany
²Particle Chemistry Department, Max Planck Institute for Chemistry, Hahn‐Meitner‐Weg 1, 55128 Mainz, Germany
³Materials Performance Centre, The University of Manchester, Oxford Road, Manchester, M13 9PL UK
Published by arrangement with John Wiley & Sons

Renazzo‐type (CR) carbonaceous chondrites belong to one of the most pristine meteorite groups containing various early solar system components such as matrix and fine‐grained rims (FGRs), whose formation mechanisms are still debated. Here, we have investigated FGRs of three Antarctic CR chondrites (GRA 95229, MIL 07525, and EET 92161) by electron microscopy techniques. We specifically focused on the abundances and chemical compositions of the amorphous silicates within the rims and matrix by analytical transmission electron microscopy. Comparison of the amorphous silicate composition to a matrix area of GRA 95229 clearly shows a compositional relationship between the matrix and the fine‐grained rim, such as similar Mg/Si and Fe/Si ratios. This relationship and the abundance of the amorphous silicates in the rims strengthen a solar nebular origin and rule out a primary formation mechanism by parent body processes such as chondrule erosion. Moreover, our chemical analyses of the amorphous silicates and their abundance indicate that the CR rims experienced progressive alteration stages. According to our analyses, the GRA 95229 sample is the least altered one based on its high modal abundance of amorphous silicates (31%) and close‐to‐chondritic Fe/Si ratios, followed by MIL 07525 and finally EET 92161 with lesser amounts of amorphous silicates (12% and 5%, respectively) and higher Fe/Si ratios. Abundances and chemical compositions of amorphous silicates within matrix and rims are therefore suitable recorders to track different alteration stages on a submicron scale within variably altered CR chondrites.

^1,2José C. Aponte,^1,2Hannah L. McLain,^1,3Danielle N. Simkus,¹Jamie E. Elsila,¹Daniel P. Glavin,¹Eric T. Parker,¹Jason P. Dworkin,⁴Dolores H. Hill,^4,5Harold C. Connolly Jr.,⁴Dante S. Lauretta
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13531]
¹Astrochemistry Laboratory, Code 691, NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA²Department of Chemistry, The Catholic University of America, Washington, District of Columbia, 20064 USA
³NASA Postdoctoral Program at NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA
⁴Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, 85721 USA
⁵School of Earth and Environment, Rowan University, Glassboro, New Jersey, 08028 USA
Published by arrangement with John Wiley & Sons

Evaluating the water‐soluble organic composition of carbonaceous chondrites is key to understanding the inventory of organic matter present at the origins of the solar system and the subsequent processes that took place inside asteroid parent bodies. Here, we present a side‐by‐side analysis and comparison of the abundance and molecular distribution of aliphatic amines, aldehydes, ketones, mono‐ and dicarboxylic acids, and free and acid‐releasable cyanide species in the CM2 chondrites Aguas Zarcas and Murchison. The Aguas Zarcas meteorite is a recent fall that occurred in central Costa Rica and constitutes the largest recovered mass of a CM‐type meteorite after Murchison. The overall content of organic species we investigated was systematically higher in Murchison than in Aguas Zarcas. Similar to previous meteoritic organic studies, carboxylic acids were one to two orders of magnitude more abundant than other soluble organic compound classes investigated in both meteorite samples. We did not identify free cyanide in Aguas Zarcas and Murchison; however, cyanide species analyzed after acid digestion of the water‐extracted meteorite mineral matrix were detected and quantified at slightly higher abundances in Aguas Zarcas compared to Murchison. Although there were differences in the total abundances of specific compound classes, these two carbonaceous chondrites showed similar isomeric distributions of aliphatic amines and carboxylic acids, with common traits such as a complete suite of structural isomers that decreases in concentration with increasing molecular weight. These observations agree with their petrologic CM type‐2 classification, suggesting that these meteorites experienced similar organic formation processes and/or conditions during parent body aqueous alteration.