^1,2Seamus L. Anderson (>10)
Meteoritics & Planetary Science (in Press), Link to Article [DOI: 10.1111/maps.70232]
¹Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, Australia
²Solar System Exploration Division, Code 690, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Published by arrangement with John Wiley & Sons

The Dingle Dell meteorite fell in the wheat belt of Western Australia on Halloween night (October 31st) in 2016 and was observed by multiple cameras from the Desert Fireball Network, being recovered less than a week later. In this paper, we report the in-depth characterization and reclassification of this meteorite, from its original LL6 class to an updated L6 chondrite. Dingle Dell is an unbrecciated L6 chondrite with low shock features (S2) and no weathering (W0). The silicate mineral chemistry is typical of an L chondrite (Fa = 24.4 ± 0.3; Fs = 20.5 ± 0.2; Wo = 1.6 ± 0.3; all mol%), while the kamacite-Co concentration is on the high end of the L-chondrite range. The measured oxygen isotopes (δ¹⁷O = 3.809 ± 0.068; δ¹⁸O = 5.102 ± 0.126; Δ¹⁷O = 1.115 ± 0.011) are slightly more consistent with an LL chondrite classification, though on the border shared by L and LL chondrites. The chromium isotopic anomaly measured in Dingle Dell also places it among both L and LL chondrites (ɛ⁵⁴Cr = −0.37 ± 0.09). Analyses of cosmogenic radionuclides and noble gases indicate that Dingle Dell existed as a small meteoroid (10–15 cm radius) for 9.3 ± 1.3 Myr before impacting the Earth. Ideal gas pycnometry indicates a grain density of 3.61 ± 0.01 g cm⁻³ and a bulk density of 3.23 ± 0.02 g cm⁻³, revealing a calculated porosity of 10.5% ± 0.5%. Dingle Dell’s likely source region near the 3:1 mean motion resonance may constitute meteoritic sampling from an asteroid not associated with the Massalia or Flora families, the proposed sources for many L chondrites.

^1,2Roger H. Hewins, ^1,3Brigitte Zanda, ¹Arnaud Duverger
Meteoritics & Planetary Science (in Press), Open Source Link to Article [DOI: 10.1111/maps.70220]
¹Muséum National d’Histoire Naturelle, Sorbonne Université, UMR CNRS 7590, Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC), Paris, France
²Earth and Planetary Sciences, Rutgers University, Piscataway, New Jersey, USA
³LTE, UMR CNRS 8255, Observatoire de Paris, Paris, France
Published by arrangement with John Wiley & Sons

Shergottites are the most abundant meteorites from Mars and a major source of information on magma reservoirs, transport, and eruption, particularly in the late Hesperian northern hemisphere. Conflicting interpretations have arisen on the crystallization conditions of pyroxene in olivine-phyric shergottites. The pyroxene Ti:Al barometer suggested deep crustal or upper mantle crystallization, while 1 bar experimental petrology yielded a similar pyroxene Al-Ti distribution but suggested near surface formation. This barometer was first calibrated for alkali basalt, in which the phases that crystallized changed as a function of pressure, and it has not been demonstrated that its application could be extended to olivine-phyric shergottites. We have confronted this question by examining the petrogenesis of NWA 6234 and NWA 10170 olivine-phyric shergottites, which we confirm are paired. Modeling of their crystallization shows that the major-element composition trend of their composite, complexly zoned pyroxene crystals cannot be reproduced, indicating disequilibrium due to rapid cooling. It also shows that, with an unchanging sequence of crystallizing phases, the partitioning of Al and Ti into pyroxene does not change with pressure. Many olivine-phyric shergottites experienced strong undercooling, as in many Apollo and terrestrial basalts, consistent with surface eruption during pyroxene crystallization.

^1,2D. K. Buckner, ²J. C. Aponte, ³A. C. Schuerger, ⁴D. I. Foustoukos, ^2,5,6F. Seguin, ⁷M. B. Wilhelm, ⁸G. Cooper, ⁹A. J. Williams
Meteoritics & Planetary Science (in Press) Open Access Link to Article [DOI: 10.1111/maps.70194]
¹NASA Postdoctoral Program, Oak Ridge Associated Universities, Oak Ridge, Tennessee, USA
²Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
³Department of Plant Pathology, University of Florida, Gainesville, Florida, USA
⁴Carnegie Institute for Science, Washington, DC, USA
⁵Center for Research and Exploration in Space Science and Technology II, Greenbelt, Maryland, USA
⁶Earth & Space Research Administration, University of Maryland—Baltimore County, Baltimore, Maryland, USA
⁷Space Science & Astrobiology Division, NASA Ames Research Center, Moffett Field, California, USA

Published by arrangement with John Wiley & Sons

In the search for life on Mars, understanding the origin of preserved organics is critical. Expected sources include exogenous delivery, endogenous synthesis, and potentially life. Environmental processing by ultraviolet (UV) irradiation can alter these organics, obscuring hallmarks of their origin. To deconvolve these effects, we conducted an experimental study subjecting the Aguas Zarcas (CM2) carbonaceous chondrite to UV–VIS–NIR (200–2500 nm) irradiation under Mars environmental conditions (8.5 mbar pressure, −4 to −7 °C temperature, Mars atmosphere mix of 95.04% CO₂, 2.59% N₂, 1.94% Ar, 0.40% O₂, and 0.03% H₂O) for 154 sols (days on Mars) equivalent exposure. We measured changes to carboxylic acid abundances and compound-specific δ¹³C isotopes and bulk carbon, nitrogen, and hydrogen weight percent and isotopes. Compared to unirradiated samples, UV-exposed samples displayed nearly a twofold increase in total carboxylic acid abundance, due to elevated quantities of formic (C₁) and acetic (C₂) acids, while indigenous longer-chained (C₃–C₆) species displayed no change in abundance. Our results suggest that on Mars, UV irradiation of carbonaceous chondrites over short time scales is unlikely to degrade indigenous carboxylic acids and additionally may represent a photochemical synthesis mechanism for producing short-chain organic acids from meteoritic insoluble organic matter (IOM), meteoritic carbonates, or atmospheric CO₂ precursors.

¹Zhi Cao, ¹Pan Yan, ¹Zhiyong Xiao, ²Yanxue Wu, ³Haiyang Xian, ¹Yunhua Wu, ⁴Lifeng Zhong, ⁵Dengfeng Li, ²Mingchao Xiong, ²Zilei Chen
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.70229]
¹Planetary Environmental and Astrobiological Research Laboratory, School of Atmospheric Sciences, Sun Yat-sen University, Zhuhai, China
²State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
³CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou, China
⁴Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China
⁵Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-sen University, Zhuhai, China
Published by arrangement with John Wiley & Sons

Microstructures on surfaces of lunar regolith particles record intricate processes during regolith formation and evolution. To acquire the complete morphology and composition of microstructures on surfaces of Chang’e-5 and Chang’e-6 regolith particles, the selected particles were rotated, cleaned using anhydrous ethanol, and loaded into electron microscopes for multiple rounds of analysis. During sample analysis, we noticed a few unusual features on the surfaces of the particles, including ferric-rich iron oxides and NaCl and KCl crystals. These features exhibit overlapping relationships with other microstructures, similar to those formed on the Moon. By comparing the before and after scanning electron microscope (SEM) images, we confirmed that these features resulted from the oxidation of metallic iron particles in the Earth atmosphere and the adhesion of terrestrial contaminants. Our results demonstrate that localized alteration and contamination of lunar regolith samples, although rare, may occur during a limited exposure to the Earth atmosphere, which might hamper interpretations of sample analysis. This work highlights the importance of full-process environmental protection (e.g., inert gas, constant temperature) for pretreatment, transfer and analysis of extraterrestrial samples.