Timing of thermal metamorphism in CM chondrites: Implications for Ryugu and Bennu future sample return

1Elsa Amsellem,1,2Frédéric Moynier,1,3Brandon Mahan,2,4Pierre Beck
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.113593]
1Université de Paris, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France
2Institut Universitaire de France, Paris, France
3Department of Earth and Planetary Sciences, Macquarie University, Sydney, New South Wales 2109, Australia
4Institut de Planétologie et d’Astrophysique de Grenoble, Univ. Grenoble Alpes, CNRS, CNES, 38000 Grenoble, France
Copyright Elsevier

Carbonaceous chondrites are often considered potential contributors of water and other volatiles to terrestrial planets as most of them contain significant amounts of hydrous mineral phases. As such, carbonaceous chondrites are candidate building blocks for Earth, and elucidating their thermal histories is of direct importance for understanding the volatile element history of Earth and the terrestrial planets. A significant fraction of CM type carbonaceous chondrites are thermally metamorphosed or “heated” and have lost part of their water content. The origin and the timing of such heating events are still debated, as they could have occurred either in the first Myrs of the Solar System via short-lived radioactive heating, or later by impact induced heating and/or solar radiation. Since Rb is more volatile than Sr, and some heated CM chondrites are highly depleted in Rb, a dating system based on the radioactive decay of 87Rb to 87Sr (λ87Rb = 1.393 × 10−11 yr−1) could be used to date the heating event relating to the fractionation of Rb and Sr. Here, we have leveraged the 87Rb/87Sr system to date the heating of five CM chondrites (PCA 02012, PCA 02010, PCA 91008, QUE 93005 and MIL 07675). We find that the heating events of all five meteorites occurred at least 3 Ga after the formation of the Solar System. Such timing excludes short-lived radioactive heating as the origin of thermal metamorphism in these meteorites, and relates such heating events to ages of collisional families of C-type asteroids.

A carbonaceous chondrite and cometary origin for icy moons of Jupiter and Saturn

1Adrien Néri,2François Guyot,1 Bruno Reynard,3Christophe Sotin
Earth and Planetary Science Letters 530, 115920 Link to Article [https://doi.org/10.1016/j.epsl.2019.115920]
1University of Lyon, ENS de Lyon, CNRS, Lyon, France
2Museum National d’Histoire Naturelle, Sorbonne Université, IMPMC, UMR CNRS 7590, IRD UMR206, Paris, France
3Jet Propulsion Laboratory-California Institute of Technology, Pasadena, CA, USA
Copyright Elsevier

The inner structure of icy moons comprises ices, liquid water, a silicate rocky core and sometimes an inner metallic core depending on thermal evolution and differentiation. Mineralogy and density models for the silicate part of the icy satellites cores were assessed assuming a carbonaceous chondritic (CI) bulk composition and using a free-energy minimization code and experiments. Densities of other components, solid and liquid sulfides, carbonaceous matter, were evaluated from available equations of state. Model densities for silicates are larger than assessed from magnesian terrestrial minerals, by 200 to 600 kg.m−3 for the hydrated silicates, and 300 to 500 kg.m−3 for the dry silicates, due to the high iron bulk concentration in CI. The stability of Na-phlogopite in the silicate fraction up to 1300 K favors the trapping of most 40K in the rocky/carbonaceous cores with important consequences for modeling of the thermal evolution of icy satellites. We find that CI density models of icy satellite cores taking into account only the silicate and metal/sulfide fraction cannot account for the observed densities and reduced moment of inertia of Titan and Ganymede without adding a lower density component. We propose that this low-density component is carbonaceous matter derived from insoluble organic matter, in proportion of ∼30-40% in volume and 15-20% in mass. This proportion is compatible with contributions from CI and comets, making these primitive bodies including their carbonaceous matter component likely precursors of icy moons, and potentially of most of the objects formed behind the snow line of the solar system.

Spectral and orbital survey of medium-sized meteoroids

1Pavol Matlovič,1Juraj Tóth,2Regina Rudawska,1Leonard Kornoš,1Adriana Pisarčíková
Astronomy & Astrophysics 629 A71 Link to Article
[https://doi.org/10.1051/0004-6361/201936093]
1Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia
2ESTEC/ESA, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands

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Multivariable statistical analysis of spectrophotometry and spectra of (162173) Ryugu as observed by JAXA Hayabusa2 mission

1M.A.Barucci et al. (>10)
Astronomy & Astrophysics 629 A13 Link to Article [https://doi.org/10.1051/0004-6361/201935851]
1LESIA, Observatoire de Paris, PSL Research University, CNRS, Université Paris Diderot, Sorbonne Paris Cité, UPMC Université Paris 06, Sorbonne Universités, 5 place Jules Janssen, 92195 Meudon, France

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Calcium Isotopic Composition of the Lunar Crust, Mantle, and Bulk Silicate Moon:A Preliminary Study

1,2Wei Wu,1,2Yi-Gang Xu,1Zhao-Feng Zhang,1Xin Li
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.12.001]
1State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
2School of Earth and Planetary Science, University of Chinese Academy of Sciences, Beijing 100049, China
Copyright Elsevier

Calcium isotopes have the potential to explore genetic links between the Moon and Earth. Here, we constrain calcium isotopic composition of the bulk silicate Moon (BSM), using petrological, geochemical and calcium isotopic data obtained from five lunar meteorites (two basalts and three feldspathic breccia rocks), and on four anorthite crystals from two feldspathic breccia meteorites. The δ44/40Ca of lunar feldspathic breccias are 0.76 ± 0.06‰ (2SD, n=3), 0.78 ± 0.10‰ (2SD, n=6) and 0.82 ± 0.02‰ (2SD, n=3), respectively, consistent with previously determined calcium isotopic composition of feldspathic breccias. Four anorthite crystals yield a mean δ44/40Ca value of 0.75 ± 0.13‰ (2SD, n=4), inferred to represent the δ44/40Ca value of the lunar crust. The δ44/40Ca values of the two lunar basalts are 0.90 ± 0.07‰ (2SD,n=3) and 0.96 ± 0.11‰ (2SD, n=4), respectively, slightly heavier than the feldspathic breccias and anorthites. The δ44/40Ca of the studied lunar basalts and literature data show negative correlations with CaO, Al2O3, and anorthite mode, pointing to the effect of contamination by lunar crust rocks. Using the heaviest δ44/40Ca found in the least contaminated lunar basalts and a 0.10–0.20‰ fractionation of calcium isotopes during partial melting, we estimate the δ44/40Ca value of the lunar mantle to be 0.96-1.11‰. The δ44/40Ca values of the BSM is estimated to be 0.89-0.95‰, using a two-end member mixing model. The Ca isotopic composition of the BSM is within error to that of the bulk silicate Earth (0.94 ± 0.05‰), providing insights into the information of the comparison of the Earth-Moon system and the planets of inner Solar System.

Thermal history modelling of the L chondrite parent body

1Hans-Peter Gail,2Mario Trieloff
Astronomy & Astrophysics 628, A77 Link to Article [https://doi.org/10.1051/0004-6361/201936020]
1Zentrum für Astronomie, Institut für Theoretische Astrophysik, Universität Heidelberg, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
2Klaus-Tschira-Labor für Kosmochemie, Institut für Geowissenschaften, Universität Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany

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