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3. Reconstructing the late accretion history of the Moon

Author

Zhu, Meng-Hua, Artemieva, Natalia, Morbidelli, Alessandro, Yin, Qing-Zhu, Becker, Harry, and Wunnemann, Kai

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

The importance of highly siderophile elements (HSEs) to track planetary late accretion has long been recognized. However, the precise nature of the Moon's accretional history remains enigmatic. There exists a significant mismatch of HSE budgets between the Earth and Moon, with the Earth disproportionally accreted far more HSEs than the Moon did. Several scenarios have been proposed to explain this conundrum, including the delivery of HSEs to Earth by a few big impactors, the accretion of pebble-sized objects on dynamically cold orbits that enhanced the Earth's gravitational focusing factor, and the "sawtooth model" with much reduced impact flux before ~4.10 Gyr. However, most of these models assume a high impactor retention ratio f (fraction of impactor mass retained on the target) for the Moon. Here, we performed a series of impact simulations to quantify the f-value, followed by a Monte Carlo procedure enacting a monotonically decaying impact flux, to compute the mass accreted into lunar crust and mantle over their histories. We found that the average f-value for the Moon's entire impact history is about 3 times lower than previously estimated. Our results indicate that, to match the HSE budget of lunar crust and mantle, the retention of HSEs should have started ~ 4.35 Gyr ago, when most of lunar magma ocean was solidified. Mass accreted prior to 4.35 Gyr must have lost its HSE to the lunar core, presumably during the lunar mantle crystallization. The combination of a low impactor retention ratio and a late retention of HSEs in the lunar mantle provide a realistic explanation for the apparent deficit of Moon's late accreted mass relative to the Earth., Comment: 31 pages, 3 figures

Published
2020
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5. Community recommendations for geochemical data, services and analytical capabilities in the 21st century

Author

Klöcking, Marthe, Wyborn, Lesley, Lehnert, Kerstin A., Ware, Bryant, Prent, Alexander M., Profeta, Lucia, Kohlmann, Fabian, Noble, Wayne, Bruno, Ian, Lambart, Sarah, Ananuer, Halimulati, Barber, Nicholas D., Becker, Harry, Brodbeck, Maurice, Deng, Hang, Deng, Kai, Elger, Kirsten, de Souza Franco, Gabriel, Gao, Yajie, Ghasera, Khalid Mohammed, Hezel, Dominik C., Huang, Jingyi, Kerswell, Buchanan, Koch, Hilde, Lanati, Anthony W., ter Maat, Geertje, Martínez-Villegas, Nadia, Nana Yobo, Lucien, Redaa, Ahmad, Schäfer, Wiebke, Swing, Megan R., Taylor, Richard J.M., Traun, Marie Katrine, Whelan, Jo, and Zhou, Tengfei

Published
2023
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21. Reconstructing the late-accretion history of the Moon

Author

Zhu, Meng-Hua, Artemieva, Natalia, Morbidelli, Alessandro, Yin, Qing-Zhu, Becker, Harry, and Wünnemann, Kai

Subjects
Moon -- Natural history, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

The importance of highly siderophile elements (HSEs; namely, gold, iridium, osmium, palladium, platinum, rhenium, rhodium and ruthenium) in tracking the late accretion stages of planetary formation has long been recognized. However, the precise nature of the Moon's accretional history remains enigmatic. There is a substantial mismatch in the HSE budgets of the Earth and the Moon, with the Earth seeming to have accreted disproportionally more HSEs than the Moon.sup.1. Several scenarios have been proposed to explain this conundrum, including the delivery of HSEs to the Earth by a few big impactors.sup.1, the accretion of pebble-sized objects on dynamically cold orbits that enhanced the Earth's gravitational focusing factor.sup.2, and the 'sawtooth' impact model, with its much reduced impact flux before about 4.10 billion years ago.sup.3. However, most of these models assume a high impactor-retention ratio (the fraction of impactor mass retained on the target) for the Moon. Here we perform a series of impact simulations to quantify the impactor-retention ratio, followed by a Monte Carlo procedure considering a monotonically decaying impact flux.sup.4, to compute the impactor mass accreted into the lunar crust and mantle over their histories. We find that the average impactor-retention ratio for the Moon's entire impact history is about three times lower than previously estimated.sup.1,3. Our results indicate that, to match the HSE budgets of the lunar crust and mantle.sup.5,6, the retention of HSEs should have started 4.35 billion years ago, when most of the lunar magma ocean was solidified.sup.7,8. Mass accreted before this time must have lost its HSEs to the lunar core, presumably during lunar mantle crystallization.sup.9. The combination of a low impactor-retention ratio and a late retention of HSEs in the lunar mantle provides a realistic explanation for the apparent deficit of the Moon's late-accreted mass relative to that of the Earth. Lunar impact simulations find an impactor-retention ratio three times lower than previously thought and indicate that highly siderophile element retention began 4.35 billion years ago, resolving accretion mass discrepancies between Earth and the Moon., Author(s): Meng-Hua Zhu [sup.1] [sup.2] , Natalia Artemieva [sup.2] [sup.3] [sup.4] , Alessandro Morbidelli [sup.5] , Qing-Zhu Yin [sup.6] , Harry Becker [sup.7] , Kai Wünnemann [sup.2] [sup.7] Author Affiliations: [...]

Published
2019
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27. Community recommendations for geochemical data, services and analytical capabilities in the 21st century

Author

Klöcking, Marthe, primary, Wyborn, Lesley, additional, Lehnert, Kerstin, additional, Ware, Bryant, additional, Prent, Alexander, additional, Profeta, Lucia, additional, Kohlmann, Fabian, additional, Noble, Wayne, additional, Bruno, Ian, additional, Lambart, Sarah, additional, Ananuer, Halimulati, additional, Barber, Nicholas, additional, Becker, Harry, additional, Brodbeck, Maurice, additional, Deng, Hang, additional, Deng, Kai, additional, Elger, Kirsten, additional, de Souza Franco, Gabriel, additional, Gao, Yajie, additional, Ghasera, Khalid, additional, Hezel, Dominik, additional, Huang, Jingyi, additional, Kerswell, Buchanan, additional, Koch, Hilde, additional, Lanati, Anthony, additional, ter Maat, Geertje, additional, Martínez-Villegas, Nadia, additional, Nana Yobo, Lucien, additional, Redaa, Ahmad, additional, Schäfer, Wiebke, additional, Swing, Megan, additional, Taylor, Richard, additional, Traun, Marie Katrine, additional, Whelan, Jo, additional, and Zhou, Tengfei, additional

Published
2023
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28. Silicon and iron isotopes in components of enstatite chondrites: Implications for metal–silicate–sulfide fractionation in the solar nebula

Author

Sikdar, Jinia, Becker, Harry, and Schuessler, Jan A.

Subjects
enstatite chondrites, isotopic evolution, iron isotopes, ddc:549, silicon istotopes
Abstract

Silicon and iron isotope compositions of different physically separated components of enstatite chondrites (EC) were determined in this study to understand the role of nebular and planetary scale events in fractionating Si and Fe isotopes of the terrestrial planet‐forming region. We found that the metal–sulfide nodules of EC are strongly enriched in light Si isotopes (δ30Si ≥ −5.61 ± 0.12‰, 2SD), whereas the δ30Si values of angular metal grains, magnetic, slightly magnetic, and non‐magnetic fractions become progressively heavier, correlating with their Mg# (Mg/(Mg+Fe)). White mineral phases, composed primarily of SiO2 polymorphs, display the heaviest δ30Si of up to +0.23 ± 0.10‰. The data indicate a key role of metal–silicate partitioning on the Si isotope composition of EC. The overall lighter δ30Si of bulk EC compared to other planetary materials can be explained by the enrichment of light Si isotopes in EC metals along with the loss of isotopically heavier forsterite‐rich silicates from the EC‐forming region. In contrast to the large Si isotope heterogeneity, the average Fe isotope composition (δ56Fe) of EC components was found to vary from −0.30 ± 0.08‰ to +0.20 ± 0.04‰. A positive correlation between δ56Fe and Ni/S in the components suggests that the metals are enriched in heavy Fe isotopes whereas sulfides are the principal hosts of light Fe isotopes in the non‐magnetic fractions of EC. Our combined Si and Fe isotope data in different EC components reflect an inverse correlation between δ30Si and δ56Fe, which illustrates that partitioning of Si and Fe among metal, silicate, and sulfidic phases has significantly fractionated Si and Fe isotopes under reduced conditions. Such isotope partitioning must have occurred before the diverse components were mixed to form the EC parent body. Evaluation of diffusion coefficients of Si and Fe in the metal and non‐metallic phases suggests that the Si isotope compositions of the silicate fractions of EC largely preserve information of their nebular processing. On the other hand, the Fe isotopes might have undergone partial or complete re‐equilibration during parent body metamorphism. The relatively uniform δ56Fe among different types of bulk chondrites and the Earth, despite Fe isotope differences among their components, demonstrates that the chondrite parent bodies were not formed by random mixing of chondritic components from different locations in the disk. Instead, the chondrite components mostly originated in the same nebular reservoir and Si and Fe isotopes were fractionated either due to gas–solid interactions and associated changes in physicochemical environment of the nebular reservoir and/or during parent body processing. The heavier Si isotope composition of the bulk silicate Earth may require accretion of chondritic and/or isotopically heavier EC silicates along with cumulation of refractory forsterite‐rich heavier silicates lost from the EC‐forming region to form the silicate reservoir of the Earth., DFG, German Research Foundation

Published
2023

43. INF: TRR 170 Data Management – Building a planetary data portal

Author

Lehmann, Elfrun, Becker, Harry, Cardoso, João, Wendel, Klaus, and Seidel, Marko

Subjects
Data repository (interdisciplinary)
Abstract

Data in the TRR170-DB repository reflect the different methods and approaches applied to investigate planet formation processes. Data include, Laboratory and other instrumental data on planetary samples Remote sensing data Geological maps Geophysical modeling data Planetary image products The TRR170-DB is also a resource for all TRR 170 researchers to exchange data and for collaborators.

Published
2022

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