A time-resolved paleomagnetic record of Main Group pallasites: Evidence for a large-cored, thin-mantled parent body

1,2Claire I. O. Nichols,2James F.J. Bryson,3Rory D. Cottrell,4Roger R. Fu,1Richard J. Harrison,5,6Julia Herrero-Albillos,7Florian Kronast,3John A. Tarduno,4Benjamin P. Weiss
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2021JE006900]
1Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Insitute of Technology, Cambridge, MA, 02139 USA
2Department of Earth Sciences, University of Oxford, Oxford, OX1 3AN UK
3Department of Earth and Environmental Sciences, University of Rochester, NY, 14627 USA
4Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
5Centro Universitario de la Defensa, Carretera de Huesca s/n, E-50090 Zaragoza, Spain
6Instituto de Nanociencia y Materiales de Aragón (INMA), CSIC—Universidad de Zaragoza, Zaragoza, 50009 Spain
7Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, 12489 Berlin, Germany
Copyright Elsevier

Several paleomagnetic studies have been conducted on five main group pallasites: Brenham, Marjalahti, Springwater, Imilac and Esquel. These pallasites have distinct cooling histories, meaning that their paleomagnetic records may have been acquired at different times during the thermal evolution of their parent body. Here we compile new and existing data to present the most complete time-resolved paleomagnetic record for a planetesimal, which includes a period of quiescence prior to core solidification as well as dynamo activity generated by compositional convection during core solidification. We present new paleomagnetic data for the Springwater pallasite, which constrains the timing of core solidification. Our results suggest that in order to generate the observed strong paleointensities ( ∼ 65 – 95 μT), the pallasites must have been relatively close to the dynamo source. Our thermal and dynamo models predict that the main group pallasites originate from a planetesimal with a large core (> 200 km) and a thin mantle (< 70 km).

Thermal Conductivity of the Martian Soil at the InSight Landing site from HP3 Active Heating Experiments

1M.Grott et al. (>10)
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2021JE006861]
1German Aerospace Center (DLR), Institute of Planetary Research, Berlin, Germany
Published by arrangment with John Wiley & Sons

The heat flow and physical properties package (HP3) of the InSight Mars mission is an instrument package designed to determine the martian planetary heat flow. To this end, the package was designed to emplace sensors into the martian subsurface and measure the thermal conductivity as well as the geothermal gradient in the 0-5 m depth range. After emplacing the probe to a tip depth of 0.37 m, a first reliable measurement of the average soil thermal conductivity in the 0.03 to 0.37 m depth range was performed. Using the HP3 mole as a modified line heat source, we determined a soil thermal conductivity of 0.039 ± 0.002 W m−1 K−1, consistent with the results of orbital and in-situ thermal inertia estimates. This low thermal conductivity implies that 85 to 95 % of all particles are smaller than 104-173 μm and suggests that soil cementation is minimal, contrary to the considerable degree of cementation suggested by image data. Rather, cementing agents like salts could be distributed in the form of grain coatings instead. Soil densities compatible with the measurements are urn:x-wiley:21699097:media:jgre21692:jgre21692-math-0001 kg m−3, indicating soil porosities of urn:x-wiley:21699097:media:jgre21692:jgre21692-math-0002 %.

A new laboratory emissivity and reflectance spectral library for the interpretation of mars thermal infrared spectral data

1G.Alemanno,1A.Maturilli,1M.D’Amore,1J.Helbert
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114622]
1Institute for Planetary Research, German Aerospace Center DLR, Rutherfordstr. 2, 12489 Berlin, Germany
Copyright Elsevier

New spectral orbital thermal infrared data of Mars are being acquired by the thermal infrared channel TIRVIM (in honor of Vassily Ivanovich Moroz) of the Atmospheric Chemistry Suite (ACS) of spectrometers on board of ExoMars2016 mission. TIRVIM encompasses the spectral range of 1.7–17 μm. A major challenge brought by the analysis of these data of planetary bodies with atmospheres is the ability to extract from the data the relevant information about the surface. Thus, laboratory work plays an essential role, providing end-member and mixture spectral data of planetary analogs to fit the orbital data by means of deconvolution techniques. At the Planetary Spectroscopy Laboratory (PSL) of the German Aerospace Center (DLR), we are performing new laboratory experiments on Martian analogs in order to provide a new and updated library of spectra optimized for the interpretation of TIRVIM data. Emissivity measurements, recorded at increasing temperatures, are coupled with reflectance measurements on fresh and thermally processed samples acquired between 1.7 and 17 μm. Building on measurements previously collected on Martian analogues, we have paid particular attention to the study of the spectral behaviour of mixtures of carbonates and phyllosilicates. The main goal of this analysis is to study the variation of the main carbonate spectral features in mixtures with a phyllosilicate component, an important factor for understanding the story of carbonates detections on planetary surfaces and to provide insights for new detections. The results obtained in this work show that the presence of a phyllosilicate component affect the appearance of the carbonate spectral features in the spectral range studied, with a stronger effect in the range between 1.7 and 5 μm. Effects of mineral type and particle size are also investigated and shown to strongly affect the spectral behaviour of laboratory samples. Finally, deconvolution techniques of laboratory emissivity spectra are studied in preparation for the interpretation of atmospherically corrected TIRVIM spectral data, showing that modelled mixtures spectra represent an acceptable reproduction of laboratory spectra of mixtures.

Petrology and classification of A-9003, A 09535, and Y-82094: A new type of carbonaceous chondrite

1,2M. Kimura,3R. C. Greenwood,4M. Komatsu,1N. Imae,1A. Yamaguchi,2R. Sato
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13704]
1National Institute of Polar Research, Tokyo, 190-8518 Japan
2Ibaraki University, Mito, 310-8512 Japan
3The Open University, Milton Keynes, MK7 6AA UK
4SOKENDAI, Hayama, Kanagawa, 240-0193 Japan
Published by arrangement with John Wiley & Sons

Most carbonaceous (C) chondrites are classified into eight major groups: CI, CM, CO, CV, CK, CR, CH, and CB. However, some are ungrouped. We studied two such chondrites, Asuka (A)-9003 and A 09535. The abundance of chondrules and matrix and chondrule sizes in these meteorites are similar to those in ordinary chondrites and unlike any known carbonaceous chondrite group. In contrast, they contain 4–6 vol% of refractory inclusions and have oxygen isotopic compositions within the range of CO and CV chondrites. Therefore, A-9003 and A 09535 are classified as C chondrites. Petrologic subtypes of A-9003 and A 09535 are 3.2. All these features closely resemble those of another ungrouped chondrite, Yamato (Y)-82094, and differ from those of any C chondrites reported by now. A-9003, A 09535, and Y-82094 likely represent a new type of C chondrite. We provisionally call them CA chondrite after Asuka in Antarctica. Our study suggests a wider range of formation conditions for C chondrites than currently recorded by the major C chondrite groups.

Revisiting the paleomagnetism of Muong Nong layered tektites: Implications for their formation process

1Jérôme Gattacceca,1Pierre Rochette,1Yoann Quesnel,2Sounthone Singsoupho
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13703]
1CNRS, Aix-Marseille Univ, IRD, INRAE, Aix-en-Provence, France
2Department of Physics, Faculty of Natural Sciences, National University of Laos, Vientiane, Laos
Published by arrangement with John Wiley & Sons

Among Australasian tektites, the so-called Muong Nong tektites stand out for their peculiar layering and blocky aspect. Although the source crater for the Australasian tektites is not known, Muong Nong tektites are generally considered as a relatively proximal ejecta. The mechanism responsible for the formation of the layering has been a matter of debate. In this work, we revisit the paleomagnetism of Muong Nong tektites. They retain a thermoremanent magnetization acquired during cooling below 585 °C in the presence of the ambient geomagnetic field, and carried magnetite in most samples, although at least one sample containing metallic iron was detected. The inclination of the paleomagnetic direction with respect to the layering plane clusters around 18 ± 12°, compatible with the inclination of the geomagnetic field for this latitude at the time of impact. This indicates that the layering of the Muong Nong tektites was subhorizontal while they were cooling below 585 °C. The preferred scenario for the formation of the layering of layered tektite is therefore by horizontal shear in pools or sheets of molten material.

Neutron capture 128Xe and 129Xe in the San Juan mass of the Campo del Cielo IAB iron meteorite: Evidence for a high fluence of thermalized neutrons

1O. Pravdivtseva,2M. E. Varela,1A. Meshik,3A. J. Campbell,2M. Saavedra,4D. Topa
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13708]
1Laboratory for Space Sciences and Physics Department, Washington University, CB1105, Saint Louis, Missouri, 63130 USA
2ICATE (CONICET-UNSJ), Avenida España 1512 sur, San Juan, J5402DSP Argentina
3Department of the Geophysical Sciences, University of Chicago, 5734 S. Ellis Ave., Chicago, Illinois, 60637 USA
4Central Research Laboratories, Natural History Museum, Burgring 7, Vienna, 1010 Austria
Published by arrangement with John Wiley & Sons

The petrographic study of the San Juan A2 polished section demonstrated textural and compositional similarities with the Campo del Cielo IAB iron meteorite, with trace element abundances in metal following the pattern of bulk Campo del Cielo. Xenon, neon, and helium isotopic compositions have been measured in radial graphite rims, massive graphite inclusions, fine-grained graphite aggregates, cliftonite, and platy graphite. Two silicate inclusions and two areas of metal were also analyzed. 3He/4He versus 4He/21Ne data for San Juan metal plot next to the values reported for the El Taco fragment of Campo del Cielo, supporting San Juan being a part of the Campo del Cielo meteorite shower. Based on the Ne isotopic composition of its components, and the observed correlation between 128Xe and 129Xe, the San Juan A fragment of Campo del Cielo was well shielded from the primary galactic cosmic ray high-energy irradiation. Its size allowed the secondary neutrons to be fairly well thermalized, receiving an equivalent (normalized to the research reactor with highly thermalized neutron spectrum) fluence of thermal and epithermal neutrons of 6.6 × 1017 n cm−2. Considering 1.8 × 108 years single-stage and constant exposure geometry irradiation history for Campo del Cielo, and assuming the identical neutron flux spectra for the research reactor and Campo del Cielo, the average thermal equivalent neutron flux for San Juan is about 1.2 × 102 n cm−2 s−1. Xe isotopic composition in the radial graphite rims and platy graphite shows evidence of live 129I in San Juan and is consistent with a mixture of iodine-derived and tellurium-derived Xe.

Exploring the environments of Martian impact-generated hydrothermal systems and their potential to support life

1Nisha K. Ramkissoon,1Stuart M. R. Turner,1Michael C. Macey,1Susanne P. Schwenzer,2Mark H. Reed,1Victoria K. Pearson,1Karen Olsson-Francis
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13697]
1AstrobiologyOU, STEM, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
2Earth Sciences Department, University of Oregon, Eugene, Oregon, 97403–1272 USA
Published by arrangement with John Wiley & Sons

Hydrothermal systems that formed as a result of impact events possess all the key requirements for life: liquid water, a supply of bio-essential elements, and potential energy sources. Therefore, they are prime locations in the search for life on other planets. Here, we apply thermochemical modeling to determine secondary mineral formation within an impact-generated hydrothermal system, using geochemical data returned for two soils on Mars found in regions that have previously experienced alteration. The computed mineral reaction pathways provide a basis for Gibbs energy calculations that enable both the identification of available geochemical energy, obtained from Fe-based redox reactions, that could be utilized by potential microbial life within these environments, and an estimate of potential cell numbers. Our results suggest that water–rock interactions occurring within impact-generated hydrothermal systems could support a range of Fe-based redox reactions. The geochemical energy produced from these reactions would be substantial and indicates that crater environments have the potential to support microbial cell numbers similar to what has been identified in terrestrial environments.

Melt inclusions in chassignite NWA 2737: A link between processes recorded in Martian meteorites and rocks at Gale crater

1Peiyu Wu,1Esteban Gazel,2Arya Udry,1Jacob B. Setera,2Amanda Ostwald
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13700]
1Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York, 14850 USA
2Department of Geoscience, University of Nevada, Las Vegas, Nevada, 89154 USA
Published by arrangement with John Wiley & Sons

Northwest Africa (NWA) 2737, one of the only three discovered Martian chassignites, provides critical constraints on the evolution of the Martian mantle and crust. Because of chassignites’ cumulative nature, they contain abundant melt inclusions (MI). MI are small droplets of melts trapped by crystals during the cooling of magma. They are critical to the study of pre-eruptive parental magma compositions, and thus, provide snapshots of the composition and evolution of Martian magmatic systems. Here, we present fractional crystallization models using parental magma composition calculated from NWA 2737 melt inclusions as starting compositions. We used the thermodynamic modeling software MELTS to model fractional crystallization of NWA 2737 parental magma compositions with a wide range of parameters (pressure, water content, oxygen fugacity). Our models show that the felsic compositions recently analyzed at the Martian surface in Gale crater, especially Sparkle and Angmaat, the two rocks thought to be analogous to the earliest continental crust on Earth, can be obtained by fractional crystallization of chassignite-like parental melts. Our results suggest a link between the processes that resulted in chassignites and the rocks analyzed in situ at Gale crater. To assess the possible scenarios for Martian magma migration and storage processes, we compared chassignites to terrestrial analogs formed via various mechanisms and proposed two mechanisms that may explain the intrusive and effusive rocks found in situ at Gale crater: (1) emplacement and fractionation in a closed-system crustal reservoir and (2) eruption of mafic to intermediate lavas of a relatively open system subject to constant replenishment.

Multispectral imaging and hyperspectral scanning of the first dissection of core 73002: Preliminary results

1Lingzhi Sun,1Paul G. Lucey,1Abigail Flom,1Chiara Ferrari-Wong,2Ryan A. Zeigler,2,3Juliane Gross,4Noah E. Petro,5Charles K. Shearer,2Francis M. McCubbin,VariousThe ANGSA Science Team
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13715]
1Department of Earth Sciences, Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Manoa, 1680 East-West Rd, Honolulu, Hawai‘i, 96822 USA
2Astromaterials Acquisition and Curation Office, NASA Johnson Space Center, Houston, Texas, 77058 USA
3Department of Earth & Planetary Sciences, Rutgers State University of New Jersey, Piscataway, New Jersey, 08854 USA
4Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA
5Institute of Meteoritics, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, 87131 USA
Published by arrangement with John Wiley & Sons

We measured the multispectral images and a hyperspectral profile during the first dissection pass of core 73002, and here, we present preliminary results. Both multispectral images and hyperspectral data show systematic darkening and reddening from bottom to top of the core, indicating an increasing maturity from the subsurface to surface soils. Our estimated FeO and TiO2 abundances are 9 (±1) wt% and 1.8 (±0.5) wt%, and their homogeneous distributions imply no compositional stratigraphy was sampled by core 73002. The in situ regolith reworking depth is about 14 cm as inferred from the optical maturity (OMAT) profile, corresponding to a time range of about 61 million years. Mineralogy and Mg# (molar Mg/[Mg+Fe]) calculated using hyperspectral data and radiative transfer modeling show as expected the core is dominated by plagioclase and low-Ca pyroxene, and the average Mg# is 61 (±10). Our work shows that spectroscopy has a great potential to be applied in the preliminary examination of future extraterrestrial samples from outside of the glovebox.

The astrophysical context of collision processes in meteorites

1Yves Marrocchi,2Marco Delbo,3Matthieu Gounelle
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13716]
1Université de Lorraine, CNRS, Centre de Recherches Pétrographiques et Géochimiques (CRPG), UMR 7358, Vandoeuvre␣les␣Nancy, F-54501 France
2Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Université Côte d’Azur, CS 34229, 06304 Nice, France
3IMPMC, Muséum national d’Histoire naturelle, CNRS, Sorbonne Universités, UMR 7590, 57 rue Cuvier, 75005 Paris, France
Published by arrangement with John Wiley & Sons

Chondrites are leftover solids from the early evolution of the solar protoplanetary disk that never experienced melting since their formation. They comprise unequilibrated assemblages of low- and high-temperature components, including volatile-rich, fine-grained matrices, Fe-Ni metal, sulfides, refractory inclusions, and chondrules. Consequently, chondrites are commonly described as pristine, primitive, or primordial rocks of the solar system. However, impact-generated secondary features are abundant in chondrites, suggesting that collisions among early-formed planetesimals and their fragmentation and reassembly have been effective throughout the evolution of the solar system. In this report, we review evidence of the major role of impacts in generating the current mineralogical and petrographic characteristics of chondrites. We provide perspective to these meteoritic features by discussing recent analyses of large-scale structures of the main asteroid belt and remote-sensing observations of asteroids. Observations at various spatial scales all attest that the “primitive” materials formed during the evolution of the solar system have largely been reprocessed, confirming previous studies that primitivity is relative, not absolute. This implies that (1) chondrites (and some differentiated meteorites) should systematically be envisioned as reprocessed and heterogeneous materials and (2) brecciated meteorites should be considered the norm and unbrecciated meteorites the exception.