^1,3Xiaojia Zeng,^1,2,3 Xiongyao Li,⁴ Dayl Martin,^1,2,3Hong Tang,^1,2,3Wen Yu,^5,6 Kang Yang,^5,6Zegui Wang,⁷Shijie Wang
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.06.011]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
²CAS Center for Excellence in Comparative Planetology, Hefei, China
³Key Laboratory of Space Manufacturing Technology, Chinese Academy of Sciences, Beijing 100094, China
⁴European Space Agency, Fermi Avenue, Harwell Campus, Didcot, Oxfordshire OX11 0FD, United Kingdom
⁵School of Mechanics and Civil Engineering, China University of Ming and Technology, Xuzhou 221116, China
⁶State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Ming and Technology, Xuzhou 221116, China
⁷State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
Copyright Elsevier

Asteroid regolith simulants (i.e., substitute materials for asteroid surface regoliths) are useful for the preparation of asteroid landing and/or sample-return missions. In this study, we report a new Itokawa asteroid Regolith Simulant (called IRS-1) as an S-type asteroid surface analogue for China’s upcoming asteroid exploration. The IRS-1 simulant was developed from mixing terrestrial minerals with appropriate particle size distributions, based on the currently available mineralogy data of S-type asteroid 25143 Itokowa and a LL6 chondrite Sulagiri. Multiple properties of this simulant are well-characterized, including mineralogy, bulk chemistry, particle size, density, mechanical properties, reflectance spectra, thermal properties, thermogravimetry, and hygroscopicity. These results demonstrate that the IRS-1 simulant has similar mineralogy, bulk chemistry, and physical properties to the target materials (i.e., Itokowa samples and LL6 chondrite Sulagiri), making this simulant a reasonable surface analogue of S-type asteroids. Based on the investigation of mechanical properties of the IRS-1 simulant and two other prepared regolith samples (i.e., L-chondrite-like IRS-1 L and H-chondrite-like IRS1H), we found that the mineralogical variations on S-type asteroids have a relatively large influence on the mechanical properties of S-type asteroid regoliths. Our studies show that the IRS-1 simulant will be appropriate for a number of scientific and engineering-based investigations where a large amount (few kilograms to hundreds of kilograms) of sample is required (e.g., technology development, hardware testing, and drilling). This study also provides an effective production approach for the future development of asteroid regolith simulants for different types of asteroid regoliths and associated applications.

^1,2Zhuqing Xue,^1,3Long Xiao,²Clive R.Neal,⁴Yigang Xu
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.06.022]
¹State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
²Department of Civil Engineering and Geological Sciences, University of Notre Dame, Notre Dame, Indiana 46556, U.S.A
³State Key Laboratory of Lunar and Planetary Science, Macau University of Science and Technology, Avenida Wai Long, Taipa, Macau, China
⁴State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China
Copyright Elsevier

We conducted a thorough analysis of the feldspathic breccia meteorite Dhofar 1428 with the aim of better understanding the composition and evolution of lunar crust. This sample comprises a heterogeneous array of lithic fragments including magnesian and ferroan anorthositic granulites, mafic granulites/granulitic breccia, basalts, and different kinds of impact melt rocks. In which, a high-Ti basalt clast comprising large zoned pyroxene was observed. Based on equilibrium melt calculations of mineral zonations from this basalt, Mg-pyroxene cores were interpreted to be formed from a light rare earth element (LREE) enriched liquid, whereas the Fe-pyroxene rims grew from an LREE-depleted magma. We propose that LREE-depleted signature of Fe-pyroxene results from co-crystallization with apatite. The Mg-pyroxenes suggest that enriched liquids with higher REE contents and different REE patterns relative to KREEP existed within lunar interior. Oscillating Ti/Al ratios across pyroxene in this basalt may indicate several magma recharge events or crystal movement within a zoned magma chamber. This feature illustrates that magmas were derived from a variety of sources around the time of formation of this basalt. In situ U-Pb dating was conducted on apatite grains within this basalt, the excellent consistence between the U-Pb Concordia age (3941±24 Ma, 2σ) and 207Pb/206Pb isochron age (3934±24Ma, 2σ) indicates the most likely crystallization age of this high-Ti basalt at ∼3940 Myr, making it one of the oldest high-Ti basalts formed on the Moon.
Magnesian anorthositic granulites are mineralogically and geochemically similar to those trace element-poor magnesian anorthositic granulites in many lunar meteorites. These magnesian granulites cannot form from simple mixing of pristine Ferroan Anorthosite and lithologies from the Mg-Suite, and do not have any affinities with KREEP or the Procellarum KREEP Terrane, and they could be important components of farside highlands.

¹Paolo A.Sossi,²Stephan Klemme,³Hugh St.C.O’Neill,²Jasper Berndt,^1,4Frédéric Moynier
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.06.021]
¹Institut de Physique du Globe de Paris, 1 rue Jussieu, F-75005, Paris, France
²Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, Correnst. 24, D48149 Münster, Germany
³Research School of Earth Sciences, Australian National University, 2601 Canberra, Australia
⁴Institut Universitaire de France, 75005, Paris, France
Copyright Elsevier

Moderately volatile elements (MVEs) are sensitive tracers of vaporisation in geological and cosmochemical processes owing to their balanced partitioning between vapour and condensed phases. Differences in their volatilities allows the thermodynamic conditions, particularly temperature and oxygen fugacity (fO₂), at which vaporisation occurred to be quantified. However, this exercise is hindered by a lack of experimental data relevant to the evaporation of MVEs from silicate melts. We report a series of experiments in which silicate liquids are evaporated in one-atmosphere (1-atm) gas-mixing furnaces under controlled fO₂s, from the Fe-“FeO” buffer (iron-wüstite, IW) to air (10^-0.68 bars), bracketing the range of most magmatic rocks. Time- (t) and temperature (T) series were conducted from 15 to 930 minutes and 1300-1550°C, at or above the liquidus for a synthetic ferrobasalt, to which 20 elements, each at 1000 ppm, were added. Refractory elements (e.g., Ca, Sc, V, Zr, REE) are quantitatively retained in the melt under all conditions. The MVEs show highly redox-dependent volatilities, where the extent of element loss as a function of fO₂ depends on the stoichiometry of the evaporation reaction(s), each of which has the general form M^x+nO_(x+n)/2 = M^xO_x/2 + n/4O₂. Where n is positive (as in most cases), the oxidation state of the element in the gas is more reduced than in the liquid, meaning lower oxygen fugacity promotes evaporation. We develop a general framework, by integrating element vaporisation stoichiometries with Hertz-Knudsen-Langmuir (HKL) theory, to quantify evaporative loss as a function of t, T and fO₂. Element volatilities from silicate melts differ from those during solar nebular condensation, and can thus constrain the conditions of volatile loss in post-nebular processes. Evaporation in a single event strongly discriminates between MVEs, producing a step-like abundance pattern in the residuum, similar to that observed in the Moon or Vesta. Contrastingly, the gradual depletion of MVEs according to their volatility in the Earth is inconsistent with their loss in a single evaporation event, and instead likely reflects accretion from many smaller bodies that had each experienced different degrees of volatilisation.

¹Jean Bollard et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.06.025]
¹Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Copenhagen DK-1350, Denmark
Copyright Elsevier

Chondrites are fragments of asteroids that avoided melting and, thus, provide a record of the material that accreted to form protoplanets. The dominant constituent of chondrites are millimeter-sized chondrules formed by transient heating events in the protoplanetary disk. Some chondritic components, including chondrules, contain evidence of the extinct short-lived radionuclide ²⁶Al (half-life of 0.73 Myr). The decay of ²⁶Al is postulated to have been an important heat source promoting asteroidal melting and differentiation. Thus, understanding the ²⁶Al inventory in the accretion regions of differentiated asteroids is critical to constrain the accretion timescales of protoplanets. The current paradigm asserts that the canonical ²⁶Al/²⁷Al ratio of ∼5 ×10⁻⁵ recorded by the oldest dated solids, calcium-aluminium refractory inclusions, represents that of the bulk Solar System. We report, for the first time, the ²⁶Al-²⁶Mg systematics of chondrules from the North West Africa (NWA) 5697 L 3.10 ordinary chondrite and Allende CV3_OxA (Vigarano type) carbonaceous chondrite that have been previously dated by U-corrected Pb-Pb dating. Eight chondrules, which record absolute ages ranging from 4567.57±0.56 to 4565.84±0.72 Ma, define statistically-significant internal isochron relationships corresponding to initial (²⁶Al/²⁷Al) ([²⁶Al/²⁷Al]₀) ratios in their precursors at the time of CAI formation at 4567.3±0.16 Ma ranging from (3.92+4.53-2.95) × 10⁻⁶ to (2.74+1.30-1.09) × 10⁻⁵. These initial ratios are much lower than those predicted by the Pb-Pb ages, corresponding to age mismatches between the Pb-Pb and ²⁶Al-²⁶Mg systems ranging from 0.69+0.54-0.44 to 2.71+0.66-0.59 Myr. All chondrules record ⁵⁴Cr/⁵²Cr compositions indicating an origin from inner Solar System precursor material and, as such, we interpret the age mismatch to reflect a reduced initial abundance of ²⁶Al in the chondrule precursors, similar to that proposed for the angrite parent body. In particular, the range of [²⁶Al/²⁷Al]₀ ratios essentially defines two groups, which are apparently correlated with the absolute ages of the chondrules. A first group, charactertized by chondrules with absolute Pb-Pb ages identical to CAIs, defines a mean [²⁶Al/²⁷Al]₀ value of (4.75+1.99-1.21) × 10⁻⁶, whereas a second group, with absolute ages ∼1 Myr younger than CAIs, record a mean mean [²⁶Al/²⁷Al]₀ of (1.82+0.57-0.40) × 10⁻⁵. We interpret this systematic variability in [²⁶Al/²⁷Al]₀ values as reflecting progressive inward transport and admixing of dust of solar composition and ²⁶Al content from the outer disk during chondrule recycling and remelting. Finally, a reduced [²⁶Al/²⁷Al]₀ ratio in chondrule precursors impacts our understanding of the accretion timescales of differentiated planetesimals if chondrules are indeed representative of inner disk material. Using the average [²⁶Al/²⁷Al]₀ ratio of (1.36±0.72) × 10⁻⁵ defined by the eight chondrules, thermal modelling constrains the accretion of differentiated planetesimals formed with this ²⁶Al inventory from ∼0.1 to ∼0.9 Myr after Solar System formation to ensure melting by ²⁶Al decay.