^1,2,3Xiaojia Zeng,¹Yingli Shang,^1,4Shijie Li,^1,4,2Xiongyao Li,⁵Shijie Wang,^1,4,2Yang Li
Earth, Planets and Space 71,38 Link to Article [https://doi.org/10.1186/s40623-019-1015-9]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China
²Key Laboratory of Space Manufacturing Technology, Chinese Academy of Sciences, Beijing, 100094, China
³University of Chinese Academy of Sciences, Beijing, 100049, China
⁴CAS Center for Excellence in Comparative Planetology, Hefei, China
⁵State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081, China

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Grzegorz Racki,^2,3Christian Koeberl
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13280]
¹Faculty of Earth Sciences, University of Silesia, ul. Będzińska 60, 41‐200 Sosnowiec, Poland
²Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria
³Department of Lithospheric Research, University of Vienna, Althanstrasse, 1090 Vienna, Austria
Published by arrangement with John Wiley & Sons

Franz von Paula Gruithuisen (1774–1852), the Bavarian medic, physician, and astronomer, enfant terrible of German science, is known for his insightful observations and many extravagant conceptions. However, since the seminal monograph of Baldwin (1949), he is also referenced for early contributions to the meteoritic origin concept of lunar craters. His most commonly cited paper of 1828 is analyzed here for the first time in some detail. For Gruithuisen, impact phenomena were only an outcome of a more general cosmogenic theory, which assumed planet and satellite growth by concentric shell‐like coalescence of the cosmic bodies. The aggregation theory thus defined was initiated in 1794 by Chladni, developed by the Bierberstein brothers and Anton Zach. Gruithuisen was notably the first person to formulate a nascent concept of lunar crater mechanics. This cratering process, as he thought, is based on an uneven gravitational subsidence of concentrically layered spherical impactors (=the solid core of comet) into the plastic sediments. Only the more resistant and heavy central portion of the body was submerging deeper, and therefore, the circular terrace‐like rim of the ring mountains was formed. Gruithuisen tried also to recognize terrestrial equivalents of large‐scale crater‐like mountains on the Moon, and speculated on other impact consequences, such as a catastrophic influence on the history of the biosphere and a cometary source of the terrestrial hydrosphere. These ideas found several conceptual followers in the vital German science of the last decades of 19th century. Thus, despite principal errors in the gravitationally penetrative cratering model, we confirm the claim of recognition of Gruithuisen as one of the founders of the impact hypothesis.

¹Steven B. Simon,^2,3Alexander N. Krot,²Kazuhide Nagashima
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13282]
¹Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, 87131 USA
²Hawai’i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Mānoa, Honolulu, Hawaii, 96822 USA
³Geoscience Institute/Mineralogy, Goethe University Frankfurt, Altenhoeferallee 1, 60438 Frankfurt am Main, Germany
Published by arrangement with John Wiley & Sons

The distribution of the short‐lived radionuclide ²⁶Al in the early solar system remains a major topic of investigation in planetary science. Thousands of analyses are now available but grossite‐bearing Ca‐, Al‐rich inclusions (CAIs) are underrepresented in the database. Recently found grossite‐bearing inclusions in CO3 chondrites provide an opportunity to address this matter. We determined the oxygen and magnesium isotopic compositions of individual phases of 10 grossite‐bearing CAIs in the Dominion Range (DOM) 08006 (CO3.0) and DOM 08004 (CO3.1) chondrites. All minerals in DOM 08006 CAIs as well as hibonite, spinel, and pyroxene in DOM 08004 are uniformly ¹⁶O‐rich (Δ¹⁷O = −25 to −20‰) but grossite and melilite in DOM 08004 CAIs are not; Δ¹⁷O of grossite and melilite range from ~ −11 to ~0‰ and from ~ −23 up to ~0‰, respectively. Even within this small suite, in the two chondrites a bimodal distribution of the inferred initial ²⁶Al/²⁷Al ratios (²⁶Al/²⁷Al)₀ is seen, with four having (²⁶Al/²⁷Al)₀ ≤1.1 × 10⁻⁵ and six having (²⁶Al/²⁷Al)₀ ≥3.7 × 10⁻⁵. Five of the ²⁶Al‐rich CAIs have (²⁶Al/²⁷Al)₀ within error of 4.5 × 10⁻⁵; these values can probably be considered indistinguishable from the “canonical” value of 5.2 × 10⁻⁵ given the uncertainty in the relative sensitivity factor for grossite measured by secondary ion mass spectrometry. We infer that the ²⁶Al‐poor CAIs probably formed before the radionuclide was fully mixed into the solar nebula. All minerals in the DOM 08006 CAIs, as well as spinel, hibonite, and Al‐diopside in the DOM 08004 CAIs retained their initial oxygen isotopic compositions, indicating homogeneity of oxygen isotopic compositions in the nebular region where the CO grossite‐bearing CAIs originated. Oxygen isotopic heterogeneity in CAIs from DOM 08004 resulted from exchange between the initially ¹⁶O‐rich (Δ¹⁷O ~−24‰) melilite and grossite and ¹⁶O‐poor (Δ¹⁷O ~0‰) fluid during hydrothermal alteration on the CO chondrite parent body; hibonite, spinel, and Al‐diopside avoided oxygen isotopic exchange during the alteration. Grossite and melilite that underwent oxygen isotopic exchange avoided redistribution of radiogenic ²⁶Mg and preserved undisturbed internal Al‐Mg isochrons. The Δ¹⁷O of the fluid can be inferred from O‐isotopic compositions of aqueously formed fayalite and magnetite that precipitated from the fluid on the CO parent asteroid. This and previous studies suggest that O‐isotope exchange during fluid–rock interaction affected most CAIs in CO ≥3.1 chondrites.

¹Ingo Leya, ¹Peter C. Stephenson
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13288]
¹Space Research and Planetology, University of Bern, Bern, Switzerland
Published by arrangement with John Wiley & Sons

We report newly measured noble gas isotopic concentrations of He, Ne, and Ar for 21 samples from the 10 ureilites, DaG 084, DaG 319, DaG 340, Dho 132, HaH 126, JaH 422, JaH 424, Kenna, NWA 5928, and RaS 247, including the results of both single and stepwise heating extractions. Cosmic ray exposure (CRE) ages calculated using model calculations that fully account for all shielding depths and a wide range of preatmospheric radii, and are tailored to ureilite chemistry, range from 3.7 Ma for Dho 132 to 36.3 Ma for one of several measured Kenna samples. In a Ne‐three‐isotope plot, the data for DaG 340 and JaH 422 plot below the Necos/Neureilite mixing envelope, possibly indicating the presence of Ne produced from solar cosmic rays. In combination with literature data and correcting for pairing, we established a fully consistent database containing 100 samples from 40 different ureilites. The CRE age histogram shows a trend of decreasing meteorite number with increasing CRE age. We speculate that the parent body of the known ureilites is moving closer to a resonance and/or that there is a loss mechanism that acts on ureilites independent of their size. In addition, there is a slight indication for a peak in the range 30 Ma, which might indicate a larger impact on the ureilite daughter body. Finally, we confirm earlier results that the majority of the studied ureilites have relatively small preatmospheric radii less or equal ~20 cm.

¹Robert M. Hazen
American Mineralogist 104, 468-470 Link to Article [https://doi.org/10.2138/am-2019-6745]
¹Geophysical Laboratory, Carnegie Institution for Science, 5251 Broad Branch Road NW, Washington, D.C. 20015, U.S.A. Orcid 0000-0003-4163-8644
Copyright: The Mineralogical Society of America

The Earth in Five Reactions Workshop posed two significant challenges: (1) the formulation of a conceptual definition of “reaction” and (2) the identification and ranking of the “most important reactions” in the context of planetary evolution. Attempted answers to those challenges, collated in this collection of articles, reflect both the opportunities and hurdles when scientists deal with questions of meaning and value.

¹Kevin J.Walsh,¹Harold F.Levison
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.03.031]
¹Southwest Research Institute, 1050 Walnut St. Suite 300, Boulder, CO 80302, USA
Copyright Elsevier

We present numerical simulations of terrestrial planet formation that examine the growth continuously from planetesimals to planets in the inner Solar System. Previous studies show that the growth will be inside-out, but it is still common practice to assume that the entire inner disk will eventually reach a bi-modal distribution of embryos and planetesimals. For the combinations of disk mass, initial planetesimal radius and gas disk lifetime explored in this work the entire disk never reaches a simple bi-modal mass distribution.
We find that the inside-out growth is amplified by the combined effects of collisional evolution of solid bodies and interactions with a dissipating gas disk. This leads to oligarchic growth never being achieved in different places of the disk at the same time, where in some cases the disk can simultaneously support chaotic growth and giant impacts inside 1 au and runaway growth beyond 2 au. The planetesimal population is efficiently depleted in the inner disk where embryo growth primarily advances in the presence of a significant gas disk. Further out in the disk growth is slower relative to the gas disk dissipation, resulting in more excited planetesimals at the same stage of growth and less efficient accretion. This same effect drives mass loss due to collisional grinding strongly altering the surface density of the accreted planets relative to the initial mass distribution. This effect decreases the Mars-to-Earth mass ratios compared to previous works with no collisional grinding. Similar to some previous findings utilizing vastly different growth scenarios these simulations produce a first generation of planetary embryos that are stable for 10–20 Myr, or 5–10 e-folding times of the gas dissipation timescale, before having an instability and entering the chaotic growth stage.

^1,2Erin L.Walton,³Nicholas E.Timms,⁴Tyler E.Hauck,²Ebberly A.MacLagan,²Christopher D.K.Herd
Earth and Planetary Science Letters 515, 173-186 Link to Article [https://doi.org/10.1016/j.epsl.2019.03.015]
¹Department of Physical Sciences, MacEwan University, City Centre Campus, 10700 104 Ave, Edmonton, AB, T5J 4S2, Canada
²Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Science Building, Edmonton, AB, T6G 2E3, Canada
³Department of Applied Geology, The Institute for Geoscience Research (TIGeR), Curtin University, GPO Box U1987, Perth, WA, Australia
⁴Alberta Geological Survey – Alberta Energy Regulator, 402 Twin Atria Building, 4999 98 Ave, Edmonton, AB, T6B 2X3, Canada
Copyright Elsevier

Hypervelocity bolide impacts deliver vast amounts of energy to the Earth’s near surface. This crustal process almost universally includes sedimentary target rocks; however, their response to impact is poorly understood, in part because of complexities due to layering, pore space and the presence of volatiles that are difficult to model. The response of carbonates to bolide impact remains contentious, yet whether they melt or decompose and liberate gases by the reaction CaCO3(s) → CaO(s) + CO2(g)↑, has significant implications for post-impact climatic effects. We report on previously unknown carbonate impact melts at the Steen River impact structure, Canada, and the first description of naturally shocked barite, BaSO4. Carbonate melts are preserved as groundmass-supported calcite-rich clasts, sampled from an up to 164 m thick, continuous sequence of crater-fill polymict breccias. Electron microscopy reveals fluidal- and ocellar-textured calcite and barite, intimately associated with silicate melt, consistent with these phases being in the liquid state at the same time. Raman spectroscopy and electron backscatter diffraction (EBSD) mapping confirm the presence of high-pressure phases – reidite and coesite – within some Steen River carbonate melt-bearing breccias. These minerals attest to the strong shock provenance of the breccia and provide constraints on their shock history. Preservation of reidite lamellae in zircon indicates a shock pressure >30 GPa <60 GPa and temperatures <1473 K. In addition to melting, we present compelling evidence for widespread (70–100%) decomposition of carbonate target rocks, mixed as lithic clasts into hot impact breccias. In this context, decomposition occurs strictly post-impact due to thermal equilibration-related heating. We demonstrate that this mechanism for CO2 outgassing is likely more widespread than previously recognized. The presence of andradite-grossular garnet serve as mineralogical markers of decomposition, analogous to limestone-replacing skarn deposits. Ca-rich garnet may therefore prove an important indicator mineral for post-shock decomposition of carbonate-bearing target rocks at other craters. These findings significantly advance our understanding of how sedimentary rocks respond to hypervelocity impact, and have wide-reaching implications for estimating the amount and timing of climatically-active volatile release due to impact events.