¹M. E. Varela,²S.-L. Hwang,³P. Shen,^1,4L. N. Garcia,¹M. Saavedra,⁵T. Maruoka,⁶M. Bose
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14120]
¹Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (ICATE), Universidad Nacional de San Juan, CONICET, San Juan, Argentina
²Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan, ROC
³Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan, ROC
⁴Instituto de Mecánica Aplicada, Universidad Nacional de San Juan, San Juan, Argentina
⁵Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan
⁶School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
Published by arrangement with John Wiley & Sons

The combined SEM and TEM studies on the metal (Fe-Ni alloy ±C) portion of the Vaca Muerta mesosiderite reveal structural and compositional evidence at micro to nanoscale, which sheds light on the solidification of taenite + graphite as a cement, and later solid-state precipitation process for the kamacite formation as grain boundary allotriomorph. Besides, it is proposed that the graphite veinlets formed through a complex partial melting process followed by a solidification toward the final eutectic transient coupled with the solid-state precipitation and later decomposition ordering of taenite. The presence of defects and taenite in graphite signal formation in a liquid environment. The δ13C values of graphite in the graphite-rich areas (e.g., ranging from −0.8 ± 1.7‰ to +15.3 ± 2.5‰) suggest a short-circuit diffusion path for C isotope fractionation.

^1,2Rhonda M. Stroud et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14128]
¹School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
²Materials Science and Technology Division, US Naval Research Laboratory, Washington, DC, USA
Published by arrangement with John Wiley & Sons

Transmission electron microscopy analyses of Hayabusa2 samples show that Ryugu organic matter exhibits a range of morphologies, elemental compositions, and carbon functional chemistries consistent with those of carbonaceous chondrites that have experienced low-temperature aqueous alteration. Both nanoglobules and diffuse organic matter are abundant. Non-globular organic particles are also present, and including some that contain nanodiamond clusters. Diffuse organic matter is finely distributed in and around phyllosilicates, forms coatings on other minerals, and is also preserved in vesicles in secondary minerals such as carbonate and pyrrhotite. The average elemental compositions determined by energy-dispersive spectroscopy of extracted, demineralized insoluble organic matter samples A0107 and C0106 are C100N3O9S1 and C100N3O7S1, respectively, with the difference in O/C slightly outside the difference in the standard error of the mean. The functional chemistry of the nanoglobules varies from mostly aromatic C=C to mixtures of aromatic C=C, ketone C=O, aliphatic (CHn), and carboxyl (COOH) groups. Diffuse organic matter associated with phyllosilicates has variable aromatic C, ketone and carboxyl groups, and some localized aliphatics, but is dominated by molecular carbonate (CO3) absorption, comparable to prior observations of clay-bound organic matter in CI meteorites.

^1,2T. H. Burbine,³R. C. Greenwood,⁴B. Zhang,⁵P. C. Buchanan
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14134]
¹Department of Astronomy, Mount Holyoke College, South Hadley, Massachusetts, USA
²Planetary Science Institute, Tucson, Arizona, USA
³The Open University, Milton Keynes, UK
⁴Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, California, USA
⁵Department of Geology, Kilgore College, Kilgore, Texas, USA
Published by arrangement with John Wiley & Sons

Asteroid 4 Vesta is typically thought to be the parent body of the HED (howardite, eucrite, and diogenite) meteorites due to spectral similarities. The discovery of asteroids far from Vesta with HED-like spectra like (1459) Magnya and HED-like meteorites (e.g., NWA 011) with anomalous oxygen isotopic values compared to typical HEDs is evidence that other Vesta-like bodies formed. We broadly define a Vesta-like body as a differentiated object with a crust composed primarily of low-Ca pyroxene and plagioclase feldspar. We estimate the number of Vesta-like bodies that did form by looking at the astronomical evidence; the oxygen isotopic, chemical, and petrologic evidence; and the iron meteorite evidence. Assuming that fragments of Vesta were scattered from Vesta by giant planet migration, we conservatively estimate that at least two Vesta-like bodies (Vesta and the Magnya parent bodies) existed. From the oxygen isotopic, chemical, and petrologic evidence, we also conservatively estimate that seven Vesta-like bodies formed. Analyses of iron meteorites indicate that there may be as many as 23 Vesta-like bodies (Vesta, 10 magmatic iron groups, South Byron trio, Emsland/Mbosi duo, 10 ungrouped irons). This estimate from iron meteorites is most certainly an overestimation due to the existence of a number of non-HED crustal/mantle fragments that potentially originated from bodies with magmatic iron cores. Using our three estimates as a guide, we predict that there were ~10 Vesta-like bodies (including Vesta) that formed in the early solar system. Only Vesta remains intact with the others being disrupted early in solar system history.