Employing magma ocean crystallization models to constrain structure and composition of the lunar interior

The process of lunar magma ocean solidification provides constraints on the properties of distinct chemical reservoirs in the lunar mantle that formed during the early evolution of the Moon. We use a combination of phase equilibria models consistent with experimental results on lunar magma ocean crystallization to study the effect of bulk silicate Moon composition on the properties of lunar mantle reservoirs. We find that the densities and relative proportions of these mantle reservoirs, in particular of the late forming ilmenite bearing cumulates (IBC), strongly depend on the FeO content of the bulk silicate Moon. This relation has implications for post-magma ocean mantle dynamics and the mass distribution in the lunar interior, because the dense IBC form at shallow depths but tend to sink towards the core mantle boundary. We quantify the relations between bulk silicate Moon FeO content, IBC thickness and bulk Moon density as well as mantle stratigraphy and bulk silicate Moon moment of inertia to constrain the bulk silicate Moon FeO content and the efficiency of IBC sinking. In combination with seismic and selenodetic constraints on mantle stratigraphy, core radius, extent of the low velocity zone at the core mantle boundary, considerations about the present day selenotherm and the effects of reservoir mixing by convection our model indicates that the bulk silicate Moon is only moderately enriched in FeO compared to the Earths mantle and contains about 9.4 - 10.9 weight percent FeO (with a lowermost limit of 8.3 weight percent and an uppermost limit of 11.9 weight percent). We also conclude that the observed bulk silicate Moon moment of inertia requires incomplete sinking of the IBC layer by mantle convection: only 20 - 60 percent of the IBC material might have reached the core mantle boundary, while the rest either remained at the depth of origin or was mixed into the middle mantle

Overturn of ilmenite‐bearing cumulates in a rheologically weak lunar mantle

©2019. American Geophysical UnionThe crystallization of the lunar magma ocean (LMO) determines the initial structure of the solid Moon. Near the end of the LMO crystallization, ilmenite‐bearing cumulates (IBC) form beneath the plagioclase crust. Being denser than the underlying mantle, IBC are prone to overturn, a hypothesis that explains several aspects of the Moon's evolution. Yet the formation of stagnant lid due to the temperature dependence of viscosity can easily prevent IBC from sinking. To infer the rheological conditions allowing IBC to sink, we calculated the LMO crystallization sequence and performed high‐resolution numerical simulations of the overturn dynamics. We assumed a diffusion creep rheology and tested the effects of reference viscosity, activation energy, and compositional viscosity contrast between IBC and mantle. The overturn strongly depends on reference viscosity and activation energy and is facilitated by a low IBC viscosity. For a reference viscosity of 1021 Pa s, characteristic of a dry rheology, IBC overturn cannot take place. For a reference viscosity of 1020 Pa s, the overturn is possible if the activation energy is a factor of 2–3 lower than the values typically assumed for dry olivine. These low activation energies suggest a role for dislocation creep. For lower‐reference viscosities associated with the presence of water or trapped melt, more than 95% IBC can sink regardless of the activation energy. Scaling laws for Rayleigh‐Taylor instability confirmed these results but also showed the need of numerical simulations to accurately quantify the overturn dynamics. Whenever IBC sink, the overturn occurs via small‐scale diapirs

Crystal Distribution in a Solidifying Lunar Magma Ocean

During its early history, the Moon experienced a phase of planetary-scale melting that is commonly referred to as the Lunar Magma Ocean (LMO). Progressive crystallization of the LMO lead to differentiation of the lunar interior into a crust and a stratified mantle. The composition of the crystallizing solids strongly depends on the degree of crystal fractionation. However, the degree of crystal fractionation in the magma ocean and its evolution with time is still poorly constrained since it depends on multiple factors, including the initial thermal state of the LMO, the ability of the magma to suspend crystals by vigorous convection or the kinetics of crystal growth and dissolution during transport in the LMO and the resulting distribution of crystals in the LMO. In this study we combine multiple modeling approaches to investigate the distribution of crystals in a solidifying magma ocean and the evolution of the crystal budget during LMO solidification

Contribution of Impact Material to the Lunar Magma Ocean Liquid and Solid Cumulates

During its accretion and early evolution, the Moon experienced an ongoing bombardment by impacting material. As a consequence, the lunar magma ocean (LMO) did not crystallize as a closed system but was influenced by the influx of accreting material that modified its thermal state and chemical composition. Depending on the size, density and degree of melting of the projectiles, impacting material could either have been mixed into the LMO or sunken through the LMO and contributed to the bottom cumulate. By combining impact and LMO solidification models, we aim to obtain quantitative information on how much of the material that accreted during LMO solidification has been mixed into the LMO liquid and how much in the solid cumulate, how the relation of these contributions changed with time and how this affected the thermochemical evolution of the LMO and the composition of lunar mantle reservoirs

A new laboratory facility in the era if sample return: the Sample Analysis Laboratory (SAL) at DLR Berlin

Introduction: Laboratory measurements of extra-terrestrial materials like meteorites and ultimately mate-rials from sample return missions can significantly enhance the scientific return of the global remote sensing data. This motivates the ongoing addition of a dedicated Sample Analysis Laboratory (SAL) to complement the work of well-established facilities like the Planetary Spectroscopy Laboratory (PSL) and the Astrobiology Laboratories within the Department of Planetary Laboratories at DLR, Berlin. SAL is being developed in prep-aration to receive samples from sample return missions such as JAXA Hayabusa 2 and MMX missions, the Chinese Chang-E 5 and 6 missions as well as the NASA Osiris-REX mission. SAL will be focusing on spectro-scopic, geochemical, mineralogical analyses at microscopic level with the ultimate aim to derive information on the formation and evolution of planetary bodies and surfaces, search for traces of organic materials or even traces of extinct or extant life and presence of water. Sample Analysis Laboratory: The near-term goal is to set up the facilities on time to receive samples from the Hayabusa 2 mission. The operations have already started in 2018 with the acquisition of a vis-IR-microscope, capable of collecting data in transmission and reflection modes between 0.4 and 20 µm and with a spot size of 50 µm. The microscope is equipped with a X,Y,Z motorized stage which allows the collection of large area maps and different magnifications. In the past months, a Field Emission Gun – electron microprobe analyzer (FEG-EMPA) an X-ray diffraction (XRD) system has been purchased. The system has a Bragg-Brentano geometry which can be switched to parallel beam geometry, equipped with a Cu Kα source, 1Der detector and automated incident beam optics. The system also allows to collect microdiffraction (μXRD) maps using a selection of different monocapillaries down to 140 µm in spot size. Currently ongoing are the acquisi-tions of a Field Emission Gun - scanning electron microscope (FEG-SEM) and a polarised light petrographic microscope. The facilities will be hosted in a clean room (ISO 5) equipped with glove boxes, stereo microscopes and mi-cromanipulator to handle and prepare samples. All samples will be stored under nitrogen gas (N2) and can be transported between the instruments with dedicated shuttles in order to avoid them to enter in contact with the external environment. Based on current planning the first parts of SAL will be operational and ready for certi-fication by early 2023. Outlook: In collaboration with the Natural History Museum in Berlin SAL will also have the expertise and facilities for carrying out curation of sample return material which will be made available for the whole Euro-pean scientific community. DLR is already curating a 0.45 mg of Lunar regolith collected from the Luna 24 Soviet mission and the first analyses of the material are being planned. SAL follows the approach of a distrib-uted European sample analysis and curation facility as discussed in the preliminary recommendation of Eu-roCares. Like other laboratory facilities at the DLR Institute of Planetary Research (such PSL and RMBL) which are part of the Europlanet RI, the new SAL will be from the start open to the scientific community. Our goal is to establish an excellence centre for sample analysis in Berlin within the next 5-10 years building on our collaborations with the Natural History Museum in Berlin and the Helmholtz Center Berlin as well as the universities in Berlin

A New Facility for the Planetary Science Community at DLR: the Planetary Sample Analysis Laboratory (SAL).

Introduction: Laboratory measurements of extra-terrestrial materials like meteorites and ultimately materials from sample return missions can significantly enhance the scientific return of the global remote sensing data. This motivated the addition of a dedicated Sample Analysis Laboratory (SAL) to complement the work of well established facilities like the Planetary Spectroscopy Laboratory (PSL) and the Astrobiology Laboratories within the Department of Planetary Laboratories at DLR, Berlin. SAL is being developed in preparation to receive samples from sample return missions such as JAXA Hayabusa 2 and MMX missions, the Chinese Chang-E 5 and 6 missions as well as the NASA Osiris-REX mission. SAL will be focusing on spectroscopic, geochemical, mineralogical analyses at microscopic level with the ultimate aim to derive information on the formation and evolution of planetary bodies and surfaces, search for traces of organic materials or even traces of extinct or extant life and presence of water. Sample Analysis Laboratory: The near-term goalis to set up the facilities on time to receive samples from the Hayabusa 2 mission. The operations have already started in 2018 with the acquisition of a vis-IR-microscope and it will continue with the acquisition of: Field Emission Gun - scanning electron microscope (FEG-SEM), Field Emission Gun – electron microprobe analyser (FEG-EMPA), X-ray diffraction (XRD) system with interchangeable optics for μXRD analysis anda polarised light microscope for high resolution imaging and mapping The facilities will be hosted in a clean room (ISO 5) equipped with glove boxes and micromanipulators to handle and prepare samples. All samples will be stored under dry nitrogen and can be transported between the instruments with dedicated shuttles in order to avoid them to enter in contact with the external environment. Based on current planning the first parts of SAL will be operational and ready for certification by end of 2022. Current facilities: To characterize and analyse the returned samples, SAL facilities will work jointly with the existing spectroscopic capabilities of PLL. PLL has the only spectroscopic infrastructure in the world with the capability to measure emissivity of powder materials, in air or in vacuum, from low to very high temperatures [1-3], over an extended spectral range from 0.2 to 200 µm. Emissivity measurements are complemented by reflectance and transmittance measurements produced simultaneously with the same set-up. Recently a vis-IR-microscope was added to extend spectral analysis to the sub-micron scale. In addition, the department is operating a Raman micro-spectrometer with a spot size on the sample in focus of <1.5 μm. The spectrometer is equipped with a cryostat serving as a planetary simulation chamber which permits simulation of environmental conditions on icy moons and planetary surfaces. PLL leads MERTIS on BepiColombo as well as the BioSign exposure experiment on the ISS. The labs have performed laboratory measurements for nearly every planetary remote sensing mission. PLL has team members on instruments on the MarsExpress, VenusExpress, MESSENGER and JAXA Hayabusa 2 and MMX missions. Most recently we joined the Hayabusa 2 Initial Sample Analysis Team.The samples analyzed at PLL range from rocks, minerals, meteorites and Apollo and Luna lunar soil samples to biological samples (e.g. pigments, cell wall molecules, lichens, bacteria, archaea and other) and samples returned from the ISS (BIOMEX) [4, 5, 6] and the asteroid Itokawa (Hayabusa sample). PLL is part of the “Distribute Planetary Simulation Facility” in European Union funded EuroPlanet Research Infrastructure (http://www.europlanet-2020-ri.eu/). Through this program (and its predecessor) over the last 9 years more than 80 external scientists have obtained time to use the PLL facilities. PLL has setup all necessary protocols to support visiting scientist, help with sample preparation, and archive the obtained data. Outlook: DLR has started establishing a Sample Analysis Laboratory. Following the approach of a distributed European sample analysis and curation facility as discussed in the preliminary recommendations of EuroCares (http://www.euro-cares.eu/) the facility at DLR could be expanded to a curation facility. The timeline for this extension will be based on the planning of sample return missions. The details will depend on the nature of the returned samples. Moreover, SAL will be running in close cooperation with the Museum für Naturkunde in Berlin and it will be operated as a community facility (e.g. Europlanet), supporting the larger German and European sample analysis community

Linking remote sensing, in situ and laboratory spectroscopy for a Ryugu analog meteorite sample

In 2022 JAXA issued an Announcement of Opportunity (AO) for receiving Hayabusa2 samples returned to Earth. We responded to the AO submitting a proposal based on using a multi-prong approach to achieve two main goals. The first goal is to address the subdued contrast of remote-sensing observations compared to measurements performed under laboratory conditions on analog materials. For this we will link the hyperspectral and imaging data collected from the spacecraft and the in-situ observations from the MASCOT lander instruments (MARA and MASCam) with laboratory-based measurements of Hayabusa2 samples using bi-directional reflectance spectroscopy under simulated asteroid surface conditions from UV to MIR/FIR achieved using three Bruker Vertex 80 V spectrometers in the Planetary Spectroscopy Laboratory. The second goal is the investigation of the mineralogy and organic matter of the samples collected by Hayabusa2, to better understanding the evolution of materials characterizing Ryugu and in general of protoplanetary disk and organic matter, investigating the aqueous alteration that took place in the parent body, and comparing the results with data collected from pristine carbonaceous chondrite analog meteorites. Spectral data will be complemented by Raman spectroscopy under simulated asteroid surface conditions, X-ray diffraction, would also allow us to define the bulk mineralogy of the samples as well as investigate the presence and nature of organic matter within the samples. In situ mineralogical and geochemical characterization will involve a pre-characterization of the sample fragments through scanning electron microscopy low voltage electron dispersive X-ray (EDX) maps, and micro IR analyses of the fragments. If allowed, a thin section of one grain will be used for electron microprobe analyses to geochemically characterize its mineralogical composition. To train our data collection and analysis methods on a realistic sample, we selected a piece of the Mukundpura meteorite, as one of the closer analogs to Ryugu’s surface (Ray et al., Planetary and Space Science, 2018, 151, 149–154). The Mukundpura chunk we selected for this study measures 3 mm in its maximum dimension, and we chose it so to have a test sample of the same size as the Hayabusa2 grain we requested in our proposal to JAXA’s AO. The test gave us confidence that we can measure with good SNR measurements in bi-directional reflectance for samples around 3 mm in size (see Figures 3, 4 below). To address our second goal the spectral data was complemented by Raman spectroscopy measured again under simulated asteroid surface conditions in our Raman Mineralogy and Biodetection Laboratory at DLR