Maximilien J. VERDIER-PAOLETTI^1,2, Yves MARROCCHI³, Lionel G. VACHER^3,4,Jerome GATTACCECA⁵, Andrey GURENKO³, Corinne SONZOGNI⁵, andMatthieu GOUNELLE^1,6
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13306]
¹IMPMC, MNHN, UPMC, UMR CNRS 7590, 61 rue Buffon, 75005 Paris, France
²Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, District of Columbia 20015, USA
³CRPG, CNRS, Universite de Lorraine, UMR 7358, Vandoeuvre les Nancy F-54501, France
⁴Department of Physics, Washington University, St. Louis, St. Louis, Missouri 63130, USA
⁵CNRS, Aix-Marseille Univ, IRD, Coll France, CEREGE, Aix-en-Provence, France
⁶Institut Universitaire de France, Maison des Universites, 103 bd. Saint-Michel, 75005 Paris, France
Published by arrangement with John Wiley & Sons

Boriskino is a poorly studied CM chondrite with numerous millimeter‐ to centimeter‐scale clasts exhibiting sharp boundaries. Clast textures and mineralogies attest to diverse geological histories with various degrees of aqueous alteration. We conducted a petrographic, chemical, and isotopic study on each clast type of the breccia to investigate if there exists a genetic link between brecciation and aqueous alteration, and to determine the controlling parameter of the extent of alteration. Boriskino is dominated by CM2 clasts for which no specific petrographic type could be assigned based on the chemical compositions and modal abundances of constituents. One clast stands out and is identified as a CM1 lithology, owing to its lack of anhydrous silicates and its overall abundance of dolomite‐like carbonates and acicular iron sulfides. We observe that alteration phases near clast boundaries exhibit foliation features, suggesting that brecciation postdated aqueous alteration. We measured the O‐isotopic composition of Ca‐carbonates and dolomite‐like carbonates to determine their precipitation temperatures following the methodology of Verdier‐Paoletti et al. (2017). Both types of carbonates yield similar ranges of precipitation temperatures independent of clast lithology, ranging from −13.9 ± 22.4 (2σ) to 166.5 ± 47.3 °C, precluding that temperature alone accounts for the differences between the CM1 and CM2 lithologies. Instead, we suggest that initial water/rock ratios of 0.75 and 0.61 for the CM1 and CM2 clasts, respectively, might control the extent of aqueous alteration. Based on these estimates, we suggest that Boriskino clasts originated from a single parent body with heterogeneous distribution of water either due to local differences in the material permeability or in the initial content of ice available. These conditions would have produced microenvironments with differing geochemical conditions thus leading to a range of degrees of aqueous alteration.

Birger Schmitz
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13308]
Astrogeobiology Laboratory, Department of Physics, Lund University, Lund, Sweden
Published by arrangement with John Wiley & Sons

One of the major frontiers in science today is the search for exoplanets, …

S. Holm-Alwmark et al. (>10)^1,2,3
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13309]
¹Department of Geology, Lund University, Solvegatan 12, SE-22362 Lund, Sweden
²Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
³Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
Published by arrangement with John Wiley & Sons

The Puchezh‐Katunki impact structure, 40–80 km in diameter, located ~400 km northeast of Moscow (Russia), has a poorly constrained age between ~164 and 203 Ma (most commonly quoted as 167 ± 3 Ma). Due to its relatively large size, the Puchezh‐Katunki structure has been a prime candidate for discussions on the link between hypervelocity impacts and extinction events. Here, we present new ⁴⁰Ar/³⁹Ar data from step‐heating analysis of five impact melt rock samples that allow us to significantly improve the age range for the formation of the Puchezh‐Katunki impact structure to 192–196 Ma. Our results also show that there is not necessarily a simple relationship between the observed petrographic features of an impact melt rock sample and the obtained ⁴⁰Ar/³⁹Ar age spectra and inverse isochrons. Furthermore, a new palynological investigation of the postimpact crater lake sediments supports an age significantly older than quoted in the literature, i.e., in the interval late Sinemurian to early Pliensbachian, in accordance with the new radioisotopic age estimate presented here. The new age range of the structure is currently the most reliable age estimate of the Puchezh‐Katunki impact event.

I. J. M. Crossfield¹, J. D. Lothringer², B. Flores^1,3, E. A. C. Mills⁴, R. Freedman^5,6, J. Valverde^1,7,8, B. Miles⁹, X. Guo¹, and A. Skemer⁹
Astrophysical Journal Letters 871, L3 Link to Article [DOI: 10.3847/2041-8213/aaf9b6]
¹Department of Physics, and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA
²Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
³Department of Physics and Astronomy, California State University Northridge, Northridge, CA, USA
⁴Department of Physics, Brandeis University, Waltham, MA, USA
⁵NASA Ames Research Center, Moffett Field, CA, USA
⁶SETI Institute, Mountain View, CA, USA
⁷Department of Physics, University of California, Santa Cruz, Santa Cruz, CA, USA
⁸Chabot-Las Positas Community College, Dublin, CA, USA
⁹Department of Astronomy, University of California, Santa Cruz, Santa Cruz, CA, USA

Low-mass M dwarfs represent the most common outcome of star formation, but their complex emergent spectra hinder detailed studies of their composition and initial formation. The measurement of isotopic ratios is a key tool that has been used to unlock the formation of our solar system, the Sun, and the nuclear processes within more massive stars. We observed GJ 745AB, two M dwarfs orbiting in a wide binary, with the NASA Infrared Telescope Facility/iSHELL spectrograph. Our spectroscopy of CO in these stars at the 4.7 μm fundamental and 2.3 μm first-overtone rovibrational bandheads reveals , , and in their photospheres. Because the stars are fully convective, the atomic constituents of these isotopologues should be uniformly mixed throughout the stars’ interiors. We find that in these M dwarfs, both / and / greatly exceed the Solar values. These measurements cannot be explained solely by models of Galactic chemical evolution, but require that the stars formed from an interstellar medium significantly enriched by material ejected from an exploding core-collapse supernova. These isotopic measurements complement the elemental abundances provided by large-scale spectroscopic surveys, and open a new window onto studies of Galactic evolution, stellar populations, and individual systems.