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Abstract New standard zircons applicable to in situ analysis of Hf/W ratio by Nanoscale secondary ion mass spectrometer (NanoSIMS) were prepared and applied to Hf-W dating of a differentiated meteorite classified as mesosiderite. The standard zircons were synthesized by high-pressure experiment from starting materials which were mixture of hafnium oxide, tungsten oxide and high-purity zircon powder. The mixed powders were stirred and pulverized by a high-energy ball mill. They were then sintered at 1000 °C and 6 GPa using multi-anvil apparatus. Homogeneity of Hf/W ratios of synthesized zircons was examined by SEM–EDS, EPMA, and Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICPMS). Hf/W ratios of the same zircons were measured by a NanoSIMS with 2 nA oxygen primary beam and mass resolving power of 10,000. The relative sensitivity factor (RSF) of Hf/W ratio was determined by comparing zircon data measured by LA-ICPMS and NanoSIMS. Observed RSF (Hf/W) of zircon is 0.585 ± 0.180 (hereafter all error 2σ) consistent with 0.855 ± 0.468 of previous work within experimental error margin. The value is higher than observed RSF of glass matrix, 0.301 ± 0.062, and significantly higher than glass data of 0.21–0.22 in references. Based on the RSF, the Hf/W ratios of zircons extracted from mesosiderite “Asuka 882,023” were measured together with W isotopic compositions by NanoSIMS. Observed data in ¹⁸⁰Hf/¹⁸⁶W–¹⁸²W/¹⁸⁶W diagram are fitted by a straight line, yielding a slope (¹⁸²Hf/¹⁸⁰Hf) of 8.19 ± 3.50 × 10^–6. This slope is converted into an absolute zircon Hf-W age of 4536.5^+4.6_–7.2 Ma using the age anchor of CV3 chondrite. This age agrees well with a reference value of 4532.0^+11.4_–20.8 Ma.

Abstract Japan Aerospace Exploration Agency's Martian Moons eXploration (MMX) mission will launch a spacecraft in 2024 to return samples from Phobos in 2029. Curatorial work for the returned Phobos samples is critical for the sample allocation without degrading the sample integrity and subsequent sample analysis that will provide new constraints on the origin of Phobos and the evolution of the circum‐Mars environment. The Sample Analysis Working Team of the MMX is designing the sample curation protocol. The curation protocol consists of three phases: (1) quick analysis (extraction and mass spectrometry for gases), (2) pre‐basic characterization (bulk‐scale observation), and (3) basic characterization (grain‐by‐grain observation and allocation of the sample aliquots). Nondestructive analyses within the clean chamber (e.g., visible and near‐infrared spectral imaging) and outside the chamber (e.g., gas mass spectrometry) are incorporated into the curation flow in coordination with the MMX mission instrument teams for ground‐truthing the remote‐sensing data sets. The MMX curation/sample analysis flow enables the seamless integration between the sample and remote‐sensing data sets to maximize the scientific value of the collected Phobos samples.

Abstract Basaltic rocks occur widely on the terrestrial planets and differentiated asteroids, including the asteroid 4 Vesta. We conducted a shock recovery experiment with decaying compressive pulses on a terrestrial basalt at the Chiba Institute of Technology, Japan. The sample recorded a range of pressures, and shock physics modeling was conducted to add a pressure scale to the observed shock features. The shocked sample was examined by optical and electron microscopy, electron back‐scattered diffractometry, and Raman spectroscopy. We found that localized melting occurs at a lower pressure (∼10 GPa) than previously thought (>20 GPa). The shocked basalt near the epicenter represents “shock degree C” of a recently proposed classification scheme for basaltic eucrites and, as such, our results provide a pressure scale for the classification scheme. Finally, we estimated the total fraction of the basaltic eucrites classified as shock degree C to be ∼15% by assuming the impact velocity distribution onto Vesta.

Shock metamorphism of minerals in meteorites provides insights into the ancient Solar System. Calcite is an abundant aqueous alteration mineral in carbonaceous chondrites. Return samples from the asteroids Ryugu and Bennu are expected to contain calcite-group minerals. Although shock metamorphism in silicates has been well studied, such data for aqueous alteration minerals are limited. Here, we investigated the shock effects in calcite with marble using impact experiments at the Planetary Exploration Research Center of Chiba Institute of Technology. We produced decaying compressive pulses with a smaller projectile than the target. A metal container facilitates recovery of a sample that retains its pre-impact stratigraphy. We estimated the peak pressure distributions in the samples with the iSALE shock physics code. The capability of this method to produce shocked grains that have experienced different degrees of metamorphism from a single experiment is an advantage over conventional uniaxial shock recovery experiments. The shocked samples were investigated by polarizing microscopy and X-ray diffraction analysis. We found that more than half of calcite grains exhibit undulatory extinction when peak pressure exceeds 3 GPa. This shock pressure is one order of magnitude higher than the Hugoniot elastic limit (HEL) of marble, but it is close to the HEL of a calcite crystal, suggesting that the undulatory extinction records dislocation-induced plastic deformation in the crystal. Finally, we propose a strategy to re-construct the maximum depth of calcite grains in a meteorite parent body, if shocked calcite grains are identified in chondrites and/or return samples from Ryugu and Bennu.

We have developed a method to analyze all rare earth elements in silicate glasses and zircon minerals using a high lateral resolution secondary ion mass spectrometer (NanoSIMS). A 2nA O⁻ primary beam was used to sputter a 7–8-μm diameter crater on the sample surface, and secondary positive ions were extracted for mass analysis using an accelerating voltage of 8 kV. A high mass resolving power of 9,400 at 10% peak height was attained to separate heavy REE from oxide of light REE. A multi-collector system combined with peak-jumping by magnetic field was adjusted to detect REEs and silicon-30 for calibration. Based on results of NIST SRM610 glass, sensitivities of REEs vary from 3 cps/ppm/nA of Lu to 13 cps/ppm/nA of Eu. Reproducibility of REE/Si ratios is better than 18% at 2σ. Secondary ion yields of REEs show positive relationships with their ionization potential of second valence. REEs of AS3, QGNG, and Torihama zircons were measured and calibrated against those of 91500 standard zircon. SIYs of REEs of zircon are identical to those of the glass standard. AS3 and QGNG data are generally consistent with those of previous work. Torihama REE data combined with the whole rock data provide partition coefficients of REEs between silicate melt and zircon. The relationship between these coefficients and ionic radius is explained by an elastic moduli model.

Abstract Japan Aerospace Exploration Agency (JAXA) plans a Phobos sample return mission (MMX: Martian Moons eXploration). In this study, we review the related works on the past climate of Mars, its evolution, and the present climate and weather to describe the scientific goals and strategies of the MMX mission regarding the evolution of the Martian surface environment. The MMX spacecraft will retrieve and return a sample of Phobos regolith back to Earth in 2029. Mars ejecta are expected to be accumulated on the surface of Phobos without being much shocked. Samples from Phobos probably contain all types of Martian rock from sedimentary to igneous covering all geological eras if ejecta from Mars could be accumulated on the Phobos surface. Therefore, the history of the surface environment of Mars can be restored by analyzing the returned samples. Remote sensing of the Martian atmosphere and monitoring ions escaping to space while the spacecraft is orbiting Mars in the equatorial orbit are also planned. The camera with multi-wavelength filters and the infrared spectrometer onboard the spacecraft can monitor rapid transport processes of water vapor, dust, ice clouds, and other species, which could not be traced by the previous satellites on the sun-synchronous polar orbit. Such time-resolved pictures of the atmospheric phenomena should be an important clue to understand both the processes of water exchange between the surface/underground reservoirs and the atmosphere and the drivers of efficient material transport to the upper atmosphere. The mass spectrometer with unprecedented mass resolution can observe ions escaping to space and monitor the atmospheric escape which has made the past Mars to evolve towards the cold and dry surface environment we know today. Together with the above two instruments, it can potentially reveal what kinds of atmospheric events can transport tracers (e.g., H₂O) upward and enhance the atmospheric escape. Graphical Abstract

火星衛星探査計画Martian Moons eXploration (MMX)は、火星衛星の一つであるフォボスからのサンプルリターンミッションである。Sample Analysis Working Team (SAWT)は、2029年に帰還するリターンサンプルの分析プロトコルの設計や、科学的要求の整理を行なっている。本発表において、MMXの科学目的である火星衛星の起源の解明等に向けて必要な分析方法と、分析チームへの分配のために必要な記載方法の検討状況を紹介する。

Japan Aerospace Exploration Agency (JAXA) will launch a spacecraft in 2024 for a sample return mission from Phobos (Martian Moons eXploration: MMX). Touchdown operations are planned to be performed twice at different landing sites on the Phobos surface to collect > 10 g of the Phobos surface materials with coring and pneumatic sampling systems on board. The Sample Analysis Working Team (SAWT) of MMX is now designing analytical protocols of the returned Phobos samples to shed light on the origin of the Martian moons as well as the evolution of the Mars-moon system. Observations of petrology and mineralogy, and measurements of bulk chemical compositions and stable isotopic ratios of, e.g., O, Cr, Ti, and Zn can provide crucial information about the origin of Phobos. If Phobos is a captured asteroid composed of primitive chondritic materials, as inferred from its reflectance spectra, geochemical data including the nature of organic matter as well as bulk H and N isotopic compositions characterize the volatile materials in the samples and constrain the type of the captured asteroid. Cosmogenic and solar wind components, most pronounced in noble gas isotopic compositions, can reveal surface processes on Phobos. Long- and short-lived radionuclide chronometry such as Mn-53-Cr-53 and Rb-87-Sr-87 systematics can date pivotal events like impacts, thermal metamorphism, and aqueous alteration on Phobos. It should be noted that the Phobos regolith is expected to contain a small amount of materials delivered from Mars, which may be physically and chemically different from any Martian meteorites in our collection and thus are particularly precious. The analysis plan will be designed to detect such Martian materials, if any, from the returned samples dominated by the endogenous Phobos materials in curation procedures at JAXA before they are processed for further analyses.

© 2020 The Author(s) The late heavy bombardment (LHB) hypothesis, wherein the terrestrial planets are thought to have suffered intense collisions ca. 3.9 billion years ago, is under debate. Coupled with new dynamical calculations, re-examination of geochronological data seem to support an earlier solar system instability and a smooth monotonic decline in impacts, as opposed to a “cataclysm.” To better understand this collisional history, records from the asteroidal meteorites are required. Here, we report a uranium–lead (U–Pb) chronological dataset for eucrite meteorites thought to originate from the asteroid 4 Vesta; this dataset indicates to a continuous history of collisions prior to 4.15 Ga. Our 207Pb⁎/206Pb⁎ model ages of apatite [Ca5(PO4)3(F,Cl,OH)] and merrillite [Ca9NaMg(PO4)7] from three brecciated basaltic eucrites—Juvinas (4150.3 ± 11.6 million years ago (Ma); merrillite only), Camel Donga (disturbed around 4570–4370 Ma), and Stannern (4143.0 ± 12.5 Ma)—record multiple thermal metamorphic events during the period of ∼4.4–4.15 Ga. We interpret this to mean that Vesta or the vestoid cluster underwent multiple impacts and moderate high-temperature reheating during this time. The ages of ∼4.4–4.15 Ga are distinctly younger than the initial magmatic process on Vesta (>4.5 Ga) but are significantly older than a later “impact peak” based on some interpretations of 40Ar–39Ar chronologies (∼3.9–3.5 Ga). The intense collisions prior to 4.15 Ga on Vesta are at odds with the conventional LHB hypothesis but not inconsistent with the much earlier bombardment and monotonic decline scenario. Different radiometric chronologies of the asteroid likely represent the different stages of a continual collisional process. Conversely, the model 207Pb⁎/206Pb⁎ ages of apatite in the unbrecciated basaltic eucrite, Agoult, returned an age of 4524.8 ± 9.6 Ma. This may represent slow cooling from an earlier global reheating of the crust on Vesta at 4.55 Ga, as documented by other radiometric chronologies. The apatite in Juvinas recorded a coincident timing of 4516.9 ± 10.4 Ma, which could be due to either slow crustal cooling or impact.

Phobos and Deimos occupy unique positions both scientifically and programmatically on the road to the exploration of the solar system. Japan Aerospace Exploration Agency (JAXA) plans a Phobos sample return mission (MMX: Martian Moons eXploration). The MMX spacecraft is scheduled to be launched in 2024, orbit both Phobos and Deimos (multiple flybys), and retrieve and return >10 g of Phobos regolith back to Earth in 2029. The Phobos regolith represents a mixture of endogenous Phobos building blocks and exogenous materials that contain solar system projectiles (e.g., interplanetary dust particles and coarser materials) and ejecta from Mars and Deimos. Under the condition that the representativeness of the sampling site(s) is guaranteed by remote sensing observations in the geologic context of Phobos, laboratory analysis (e.g., mineralogy, bulk composition, O-Cr-Ti isotopic systematics, and radiometric dating) of the returned sample will provide crucial information about the moon's origin: capture of an asteroid or in-situ formation by a giant impact. If Phobos proves to be a captured object, isotopic compositions of volatile elements (e.g., D/H, C-13/C-12, N-15/N-14) in inorganic and organic materials will shed light on both organic-mineral-water/ice interactions in a primitive rocky body originally formed in the outer solar system and the delivery process of water and organics into the inner rocky planets.

火星衛星探査計画(MMX)は火星衛星フォボスからのサンプルリターン計画であり、2024年に探査機打上げを予定している。本計画では、コアリングおよび空気圧サンプリング機構により表層レゴリス試料を10 g以上回収することを目標としている。試料分析ワーキングチーム(SAWT)は現在、回収試料の分析プロトコルを作成中である。まず、試料の岩石鉱物学的観察、全岩化学組成および同位体組成から、フォボス材料物質の起源に関する情報を得る。フォボス表面で起こるプロセスは、希ガスの同位体比や試料表面の宇宙風化組織の詳細観察によって明らかになる。さらに、放射性核種による年代測定は、フォボス物質の変成作用など重要なイベントに時間的制約を与える。また、フォボスレゴリスには小天体衝突によって火星から放出された物質が少量含まれると予想されている。フォボス表面に存在するであろう火星物質は極めて貴重な試料であり、そうした物質をキュレーションの段階において発見するための手順・方法についても議論を進めている。

本発表は、2020年代に行われる火星衛星からのサンプルリターン計画(MMX: Martian Moons eXploration)によってもたらされるフォボス試料の科学意義に関する発表を行う。

The vestiges of life in Eoarchean rocks have the potential to elucidate the origin of life. However, gathering evidence from many terrains is not always possible(1-3), and biogenic graphite has thus far been found only in the 3.7-3.8 Ga (gigayears ago) Isua supracrustal belt(4-7). Here we present the total organic carbon contents and carbon isotope values of graphite (d13Corg) and carbonate (delta(13)Ccarb) in the oldest metasedimentary rocks from northern Labrador(8,9). Some pelitic rocks have low delta(13)Corg values of -28.2, comparable to the lowest value in younger rocks. The consistency between crystallization temperatures of the graphite and metamorphic temperature of the host rocks establishes that the graphite does not originate from later contamination. A clear correlation between the delta(13)Corg values and metamorphic grade indicates that variations in the delta(13)Corg values are due to metamorphism, and that the pre-metamorphic value was lower than the minimum value. We concluded that the large fractionation between the delta(13)Ccarb and delta(13)Corg values, up to 25%, indicates the oldest evidence of organisms greater than 3.95 Ga. The discovery of the biogenic graphite enables geochemical study of the biogenic materials themselves, and will provide insight into early life not only on Earth but also on other planets.

Mesosiderites are unique stony-iron meteorites, composed of eucrite-like silicates and Fe-Ni metals. Their formation, including silicate-metal mixing and metamorphisms, provides important insights into early planetary processes in the inner solar system. This report describes the first in situ U-Pb and Hf-W dating of zircon in a mesosiderite Asuka 882023. The U-Pb (4502 +/- 75 Ma) and Hf-W (4532.8 + 5.7/-10.5 Ma) ages may represent timing of the zircon formation, which is considerably younger than crustal differentiation of the parent body. This evidence, combined with earlier studies of chronology, implies that mesosiderites were reheated at 4530-4520 Ma, clearly after the silicate-metal mixing.

<p>地球型惑星の形成進化史とその際の揮発性元素の関わりを理解する上で、太古の分化隕石中のリン酸塩鉱物が記録する地球化学的情報は非常に重要である。本研究では、小惑星ベスタ起源とされるユークライト隕石、及び、異なる母天体由来の分化隕石であるIbitiraについて、リン酸塩鉱物のU-Pb年代を調べた。さらに、NanoSIMSによる微小領域(10ミクロン)の希土類元素分析法を同一鉱物に適用し、母天体マグマの進化史を議論した。</p> <p>Some differentiated achondrites, such as eucrites, recorded ancient geochemical /geophysical processes of early asteroids (or planetesimals), including their acquirement of volatiles. Chronological and geochemical information of phosphates in the meteorites is expected as valuable clue. Here, we report the high spatial resolution U-Pb dating and rare earth elements analyses of phosphates in several basaltic eucrites and an anomalous achondrite, Ibitira. </p>

We measured the hydrogen isotopic composition (D/H ratios) and U-Pb chronology of phosphate minerals in a young Martian meteorite: LAR 06319. D/H ratios of melt-inclusions in the meteorite were also investigated to evaluate the presence of water reservoirs on Mars in recent times. The total Pb/U dating of multiple grains of apatite and merrillite yield a concordant date of 167 +/- 57 Ma, interpreted as the crystallization age, suggesting that both apatite and merrillite in this meteorite have preserved their igneous histories. The D/H ratios of an apatite grain show good reproducibility yielding a delta D value of 4250 +/- 120%, whereas those of merrillite show larger D/H variations with the maximum delta D value of 5260 +/- 790%. However, mafic glass in melt-inclusions shows extremely large variation in delta D, ranging from ca. 1070% to 6830 +/- 460%. The different D/H signatures recorded in these phases reflect the contributions of different hydrous components with distinct D/H ratios, possibly incorporated at different times. It is inferred that several isotopically distinct water reservoirs exist in the present Martian surface/sub-surface system.

Phosphate minerals, which are ubiquitous in terrestrial and extra-terrestrial rocks, are important carriers of trace elements, including U and Th, which provide chronological information because of their radioactive decay. Abundance and grain sizes of the phosphates are limited in extra-terrestrial materials. Therefore, high resolution and minimally or non-destructive analytical methods must be used for age determination. For this study, we conducted U-Pb dating using a NanoSIMS for three phosphate grains from an old Martian meteorite: ALH 84001. The (238)-U-Pb-206 and Pb-207-Pb-206 isochron ages were found to be 3850 +/- 170 Ma and 4002 +/- 52 Ma, respectively, suggesting a concordant signature at approx. 4.0 Ga. A total Pb/U isochron age of 3990 +/- 160 Ma is consistent with a previous SHRIMP U-Pb age of 4018 +/- 81 Ma (Terada et al., 2003). Moreover, heterogeneous distributions of U are observed in these grains, which might have been preserved since igneous crystallization of the phosphates because the diffusion of U in the mineral is considerably slow.

This paper describes the development of a technique using NanoSIMS to make precise and accurate determination of the hydrogen isotopic composition and the hydroxyl content of apatite grains. An experiment was also performed to determine the effects, if any, of using secondary electron microscopy (SEM) and electron probe micro-analysis (EPMA) on the mobility of volatile elements (H) in apatite grains, prior to analysis by secondary ion mass spectrometry (SIMS). The results of the experiment show that using a relatively low beam current, for a short exposure time, did not have adverse effects on the mobility of H with no apparent change in the measured D/H ratio from or within a grain. Thus, based on our study, we suggest that routine SEM analysis can indeed be used to locate suitable apatite grains for SIMS analyses without jeopardising the hydrogen isotopic measurements. As such, apatite grains were located in the studied sections using SEM and the hydrogen isotopic compositions of the lunar apatite grains from two Apollo mare basalts were determined using NanoSIMS. The delta D values for the samples analysed ranges from similar to 600 to 1000 parts per thousand and OH content from 1200 to 4400 ppm. The measurements of delta D and OH contents in apatites, performed in this study, are consistent with previous results for 10044 but the new dataset for 12064 consists of a larger range in delta D values and OH contents than previously documented. We used a raster size of 10 x 10 mu m (with data collected from a 5 x 5 mu m area) for each analysis and obtained typically +/- 40 to 80 parts per thousand precision at the 2 sigma-level. This demonstrates the capability of using the NanoSIMS 50L to accurately measure D/H ratios and OH contents in apatites containing more than 300-400 ppm OH. The coupled hydroxyl abundance and hydrogen isotopic composition data permitted an assessment of the potential D/H fractionation which may have occurred during magmatic degassing, which may ultimately be responsible for the relatively high delta D signatures of apatites from mare basalts. (C) 2012 Elsevier B.V. All rights reserved.