China’s first Mars exploration mission (HuoXing-1) has been named as ‘Tianwen-1’ meaning Heaven Inquiry. Tianwen-1 was launched on July 23, 2020. In this paper, the scientific objectives of earlier ...and current Mars exploration missions worldwide are reviewed, and the scientific objectives, payloads and preliminary scientific investigation plan of China’s first Mars exploration mission are introduced, and expected scientific achievements are analyzed.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
An exceedingly small number of high‐pressure polymorphs have been discovered in lunar samples. This situation does not seem to reconcile with the prolonged, intense bombardment of the lunar surface, ...which should produce suitable conditions for the formation of such polymorphs. Here we report the discovery of reidite, a high‐pressure polymorph of ZrSiO4 with scheelite structure in lunar meteorite Sayh al Uhaymir (SaU) 169. The reidite occurs mainly as lamellae hosted within zircon, likely corresponding to a deviatoric‐dominated transformation. The presence of reidite in the regolith portion of SaU 169 indicates a narrow temperature and pressure path constrained by the phase stability under low pressure and suggests heterogeneous shock features in the porous lunar regolith where the ambient temperature increases much higher than that in compact rocks. The inventory of high‐pressure polymorphs might be restricted by such unusual cooling processes lunar samples experienced.
Plain Language Summary
The most striking phenomenon on the Moon's surface is the densely distributed impact craters. Asteroid impacts generate high pressure and temperature conditions, resulting in the formation of high‐pressure minerals. However, only few high‐pressure minerals have been discovered in very few lunar samples so far. In this study, we first discovered reidite, a high‐pressure polymorph of ZrSiO4, in the regolith portion of lunar meteorite Sayh al Uhaymir (SaU) 169. Previous research produced reidite by applying shock pressure of >30 GPa on zircon and found that it back‐transformed to zircon quickly at temperature of >1473 K under ambient pressure. Impact into porous lunar regolith will lead to a huge increase in ambient temperature. For a postshock temperature of <1473 K, the estimated average peak pressure should not have exceeded ~10 GPa. Therefore, we suggest that reidite formed in localized high‐pressure regions (>30 GPa) induced by an impact with an average peak pressure <10 GPa. In addition, shock‐induced high ambient temperature conditions in porous lunar regolith are not favorable for the preservation of most high‐pressure minerals, therefore might restrict the observation of high‐pressure minerals in lunar samples which were mostly derived from the porous regolith layer.
Key Points
We discovered reidite, a high‐pressure polymorph of ZrSiO4, in the regolith breccia of lunar meteorite Sayh al Uhaymir 169
The reidite could have formed under localized transient pressure spikes during initial stage of asteroid impact into porous lunar regolith
High postshock temperature of porous lunar regolith likely inhibits the widespread preservation of high‐pressure polymorphs in lunar samples
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Aluminum-rich (Al2O3 > 10 wt%) chondrules (ARCs) are important chondritic components that petrologically link two other major chondritic components, ferromagnesian chondrules (FMCs) and ...calcium-aluminum-rich inclusions (CAIs), which formed in different regions of the protoplanetary disk. They are closely related to FMCs as indicated by their similar igneous textures, mineral assemblages, and Al-Mg isotope systematics; meanwhile, they have genetic a relationship with CAIs as indicated by their distinctly Al2O3-rich compositions and occasional occurrences of relict CAI minerals. In order to further understand their formation mechanism and genetic relationships to FMCs and CAIs, nine ARCs and three ARC-related objects from Allende (CV3 oxidized), Leoville (CV3 reduced), and the ungrouped Ningqiang carbonaceous chondrites were studied for petrology, mineralogy, bulk compositions, rare earth element (REE) abundances, and in situ oxygen isotopic compositions. Our results suggest that (i) ARCs crystallized from incompletely molten droplets with crystallization sequences mainly determined based on their bulk compositions. Projection of their bulk compositions onto the forsterite-saturated tridymite-diopside-spinel diagram allows us to classify them into Al-rich Sp, Al-rich En, and Al-rich Plag; (ii) ARC precursors are mixtures of refractory materials and the precursors of FMCs, in which the refractory materials have diverse sources rather than a single type of CAI/AOA (amoeboid olivine aggregate); this is inferred from the bulk compositions, relict minerals (both coarse- and fine-grained spinel, olivine, and Al-Ti-diopside), and various CAI-like REE patterns (unfractionated Group I/III and highly fractionated Group II/II-like) of ARCs. The sources include AOAs and igneous Type B/C CAIs; (iii) ARCs were melted in the FMC-forming region, possibly by the same heating mechanism or during the same transient heating event, which is consistent with the similar oxygen isotopic compositions of their phenocrysts (Δ17O = −5.2 ± 1.7‰, 2SD). Thus, we consider that ARCs formed by melting of mixtures of diverse refractory components with the FMC precursors in the FMC-forming region.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We report occurrences of coesite in a martian meteorite, expanding previously-reported silica polymorphs such as stishovite (El Goresy et al., 2000), seifertite (Sharp et al., 1999; Goresy et al., ...2008), and post-stishovite (El Goresy et al., 2000). The coesite was found in the shock-induced melt regions of NWA 8657, usually coexisting with deformed quartz and silica glass. Three morphological types of coesite have been identified: (I) in a silica-maskelynite assemblage, (II) needle grains, and (III) granular grains embedded in maskelynite. Transmission Electron Microscopy (TEM) shows that all types of coesite appear distributed in silica glass and/or nano-phase maskelynite. The stishovite-like morphology of Type II coesite and the presence of deformed quartz suggest coesite to have inverted from stishovite during decompression. The impact-induced peak pressures and temperatures are estimated at ∼ 18–30 GPa and ∼2000 ℃ respectively, based on static high pressure experiments (Langenhorst and Deutsch, 2012; Zhang et al., 1996). The polymorphs aggregates of silica in NWA 8657 indicate that the shock-induced melts in this meteorite cooled slower than those in other stishovite-bearing martian meteorites, but fast enough to preserve coesite.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We present high-precision mass-dependent nickel isotopic data for a comprehensive suite of achondrites and lunar rocks, providing key insights into the early planetary differentiation and Earth-Moon ...system formation. The primitive achondrites display high Ni contents and invariant Ni isotopic compositions. Incomplete core-mantle differentiation in primitive achondrite parent bodies resulted in the retention of metal in the mantle, which dominated the Ni budget and accounted for the bulk chondritic Ni isotopic values. The highly reduced differentiated achondrites, aubrites and an ungrouped achondrite (NWA 8409), have variable, and extremely light Ni isotopic compositions. Acid leaching experiments demonstrate that the sulfides are a significant host of light Ni isotopes in aubrites. The most extreme Ni isotope values of aubrites may be due to large Ni isotope fractionation accompanied by silicate-sulfide-metal separation during differentiation of the parent bodies, and subsequent global disruptive collision and reassembly with variably high proportions of sulfides enriched in the mantle. The howardite-eucrite-diogenite (HED) meteorites show Ni isotopic variations that are positively correlated with Ni/Co ratios, a feature that cannot be produced by igneous differentiation. Late accretion of high-Ni and high-Ni/Co chondritic materials after core formation of their likely parent body, Vesta, could have accounted for this correlation. Thus, the primitive silicate mantle of Vesta may have sub-chondritic Ni isotopic compositions, implying possible Ni isotope fractionation during core-mantle differentiation of small planetary bodies. The lunar breccia meteorites have homogenously chondritic Ni isotope values, together with their high Ni/Co of bulk rock and metals therein, suggesting impact contamination. Lunar basalt meteorites have low Ni/Co ratios and are systematically isotopically lighter than the breccias, displaying a positive correlation between Ni isotope value and Ni/Co ratio, as that seen in the HEDs. Therefore, the Ni isotopic systematics in lunar rocks also indicates the effect of late accretion, with the primitive lunar mantle having sub-chondritic Ni isotope values. This implies that the Moon-forming impactor, Theia, was likely an aubrite-like differentiated planetary body whose mantle was enriched in light Ni isotopes. We suggest that there was significant Ni isotope fractionation between core and mantle during differentiation of early formed small planetary bodies, but this signature can be obscured by late accretion in the bulk achondrite records.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The Moon and most extraterrestrial objects are lacking in water; thus, electromagnetic waves can penetrate deep into the ground and bring some structural information about the regolith and ...surrounding rocks. As an important assistant to the existing payloads, ground penetrating radar (GPR) is particularly suitable for deep space exploration, which is feasible and necessary for detecting the subsurface structures (mainly associated with the dielectric permittivity variations) of extraterrestrial objects. Unfortunately, there are not enough reference GPR profiles or drills on the extraterrestrial objects to constrain the acquired data. Here, we construct some typical models and perform numerical simulations. To make the results reasonable, various factors are considered, including the type, scale, and location of the abnormal bodies. Then, we review the reflecting phenomenon under the ground and perform comparative analyses on the reflection characteristics of different models. Finally, we present some criteria for identifying different reflectors using critical patterns of reflections. The configuration of our numerical experiments is comparable to that of the lunar penetrating radar onboard the Yutu-1 and -2; thus, the results would be reliable to support the geological interpretation of detected records as well as possible GPR detection on extraterrestrial objects in the future. This work is helpful for recognizing the reflection characteristics of the observed GPR data and would be beneficial to uncovering more critical details of subsurface structures.
•Constructing typical models of electrical properties in different sizes•Simulating sublunar wave phenomena numerically with finite-difference method•Extracting reflection characters caused by the shapes and depths of abnormal bodies•Presenting some criteria to identify typical reflectors with the patterns of reflections•Providing some references and constraints for geologically interpreting radar data
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The solar system could be separated into two zones based on the isotopic dichotomy between non-carbonaceous and carbonaceous groups, with the latter likely accreted in the outer solar system. Among ...carbonaceous groups, the CM chondrite contains high abundances of organic carbon and water. They have undergone aqueous alteration, thermal metamorphism and brecciation to different degrees (e.g., Rubin et al., 2007; Tonui et al., 2014; Zolensky et al., 1997), which contributed to erasing most of the solar nebular records. Asuka 12169 was reported as the most primitive CM chondrite based on petrological and geochemical results, with little aqueous alteration (Kimura et al., 2020). In this paper, we report a survey of presolar grains in the fine-grained matrix and the accretionary rims of chondrules and CAIs in this meteorite, based on NanoSIMS mapping of C-, O-, and Si-isotopes. A total of 158 presolar grains were identified, including 119 silicates/oxides (208 ± 20 ppm), 38 SiC (73 ± 12 ppm) and 1 carbonaceous grain (2-2+5 ppm). These abundances are within the maximum abundance ranges of primitive chondrites (80–280 ppm for O-rich grains and 10–180 ppm for C-rich grains). In comparison with most CM chondrites (<40 ppm), Asuka 12169 is uniquely rich in presolar silicates (185 ± 18 ppm), with a high presolar silicate/oxide ratio of ∼8, therefore providing robust evidence for little aqueous alteration. The high abundances of presolar SiC and silicates in Asuka 12169 clearly show its pristine properties regarding both thermal and aqueous alteration. Group 1, 2, 3 and 4 subtypes of presolar O-rich grains account for 84%, 2.5%, 0.8% and 12.6%, respectively. One O-rich grain shows a high enhancement in 17O/16O and a subsolar 18O/16O ratio (17O/16O = 6.45 ± 0.09 × 10−3 and 18O/16O = 1.90 ± 0.02 × 10−3), indicating a stellar origin in binary star systems or novae. Most identified presolar SiC are mainstream grains of AGB origins. One with 28Si-excess is classified as an X grain, suggesting a supernova origin. There are two SiC grains that have 12C/13C < 10 but close-to-solar Si isotopic ratios, and are therefore classified as AB type. The pristine features of Asuka 12169 suggest that it was probably located in the outermost few kilometers of the CM asteroid, where temperature was high enough for sublimation of water ice under vacuum, but where no aqueous alteration occurred, and where the depth was enough for lithification. The high abundances of various types of presolar grains, together with the petrographic information of Asuka 12169, provide crucial constrains on the original properties and subsequent evolution of the CM asteroids.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The ungrouped achondrite NWA 7325 is a cumulate olivine gabbro (Irving et al., 2013). It contains abundant and unique micro-inclusions of Ca-pyroxene (Bischoff et al., 2013) and spinel-like Al-Mg ...oxide (Goodrich et al., 2017) in plagioclase, indicating a remelting event induced either by impact (Goodrich et al., 2017) or by magma intrusion (Bischoff et al., 2013; Weber et al., 2016). In this work, a combined FIB-TEM study has been conducted on these micro-inclusions to address their petrogenesis and the related history of NWA 7325. TEM study revealed that micro-inclusions in the interiors of large plagioclase grains are Al-enriched spinel (Mg/Al atomic ratio: 0.03–0.4) with minor needle-like α-corundum, whereas those in the margins are predominantly Al-rich diopside (En44.5-46.6Fs1.2-1.5Wo31.2-36.7CaTs17.6-22.4) with minor forsterite (Fo94.6-94.7). The Mg/Al atomic ratios of the spinel micro-inclusions are negatively correlated with the distance away from the interface of plagioclase-pyroxene. Large plagioclase grains also exhibit a decrease in the Mg/Al atomic ratio from the rims to the cores. Based on the reaction texture at the interfaces of plagioclase-pyroxene, we infer that the Mg concentration gradient in large plagioclase grains could have resulted from Mg diffusion from the remelted rims of pyroxene into plagioclase. In addition, TEM observations showed that large plagioclase grains are not single crystals, but assemblages of submicron to micron-sized crystals. The preservation of Mg concentration gradients, submicron-sized polycrystalline plagioclases, and the consistent presence of micro-inclusions within large plagioclase grains likely indicate complete remelting of plagioclase and partial remelting of pyroxene (only rims of pyroxene with plagioclase) followed by fast cooling. We propose that micro-inclusions of diopside, forsterite, Al-rich spinel and corundum crystallized from the melt, which developed a Mg concentration gradient during the remelting of NWA 7325.
The heating temperatures of pyroxene and plagioclase in the remelting event were estimated to be 1274–1327 °C and ≥1530 °C, respectively. A subsequent cooling rate of ∼500–650 °C/h at 1300 °C was found by fitting the measured Mg concentration gradient in large plagioclase grains with a Fick’s second law model that incorporated the diffusion coefficients of Mg in plagioclase-melt. These results are better explained by a shock event; a magmatic intrusion process is ruled out. To achieve the coexistence of shock-induced high temperature (≥1274 °C) in-situ melting and only undulatory extinction of forsterite grains, an ambient temperature of 1000–1100 °C in the surrounding, parent rock of NWA 7325 was required prior to impact. This work suggests a very early shock event when NWA 7325 was hot and buried in the crust of its parental planetesimal, which is a scenario consistent with its magma crystallization age (∼4.3 Ma after CAIs, e.g., Koefoed et al., 2016). This work also implies that impacts are a potential heat source for melting hot planetesimals in the early Solar System.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This study investigated the particle size‐ and age‐dependent mixing structures of individual particles in clean and polluted air. Aerosols were classified into eight components: sea salt, mineral ...dust, fly ash, metal, soot, sulfates, nitrates, and organic matter (OM). Based on our aerosol classification, a particle that consists of two or more aerosol components can be defined as an internally mixed particle. Otherwise, it is considered to be an externally mixed particle. Within the internally mixed particle class, we identified four heterogeneous mixing structures: core‐shell, dumbbell, OM coating, and dispersed OM, as well as one homogeneous‐like mixing structure. Homogeneous‐like mixing mainly occurred in fine particles (<1 µm), while the frequency of heterogeneously mixed particles increased with particle size. Our study demonstrated that particle mixing structures depend on particle size and location and evolve with time. OM‐coating and core‐shell structures are important indicators for particle aging in air as long as they are distant from specific emission sources. Long‐range transported particles tended to have core‐shell and OM‐coating structures. We found that secondary aerosol components (e.g., sulfates, nitrates, and organics) determined particle mixing structures, because their phases change following particle hydration and dehydration under different relative humidities. Once externally mixed particles are transformed into internally mixed particles, they cannot revert to their former state, except when semivolatile aerosol components are involved. Categorizing mixing structures of individual particles is essential for studying their optical and hygroscopic properties and for tracing the development of their physical or chemical properties over time.
Key Points
Our study systematically identifies mixing structures within internally mixed particles
Particle mixing structures depend on particle size and location and they evolve over time
Secondary aerosol formation mainly determined particle mixing structures in this study
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Polynuclear aromatic hydrocarbons (PAHs) and black carbon (BC) in sediments are powerful tools in the identification of the combustion process throughout geologic history. In this study, ...combustion-derived PAHs and BC were carefully investigated in sediments from the Global Stratotype Section and Point of the Permian–Triassic (P/Tr) boundary in Meishan, China. Quantitative analyses of combustion-derived PAHs and BC demonstrate anomalously high concentrations in the boundary event beds that coincide with the mass extinction horizon. The prevalence of parent polynuclear aromatics (e.g., phenanthrene) in PAHs, together with non-metric multidimensional scaling analysis, confirms that the PAHs are mainly derived from vegetation burning instead of having a coal and/or oil origin. BC detected in sediment occurs in various forms from large irregular charcoal particles to fine aciniform soot, with an equivalent reflectance of up to 3.5%. The results strongly suggest that a wildfire occurred during the P/Tr boundary, which served as one of the possible triggers of mass extinction on land. The wildfire occurrence indicates that the O
2 concentration of the atmosphere during (or before) the P/Tr mass extinction was probably >17%. The temporal coincidence of the mass extinction with intensive volcanic eruption, marine anoxia and wildfire events in the region of the Meishan section provides new insight into the mechanisms of the P/Tr biotic crisis. Our results show that wildfires could have played an important role in the collapse of the ecosystem in the Meishan P/Tr events.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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