¹Takayuki Ushikubo,²Makoto Kimura
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.11.003]
¹Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 200 Monobe-otsu, Nankoku, Kochi 783-8502 Japan
²National Institute for Polar Research, 10-3 Midoricho, Tachikawa, Tokyo 190-8518 Japan
Copyright Elsevier

Oxygen-isotope ratios of olivine in type I (MgO-rich) and type II (FeO-rich) chondrules and olivine fragments in the matrix from the Tagish Lake meteorite (C2-anomalous) were measured to understand the characteristics of the formation environment of the Tagish Lake chondrules. Of the 43 samples analyzed, 31 are MgO-rich and 16O-rich (Δ17O ∼ −5‰ [= δ17O – 0.52 × δ18O]), which is typical of chondrules in CM, CO, and CV chondrites. Six samples are FeO-rich and 16O-poor (Δ17O ∼ −2‰), while three samples are FeO-rich chondrules with Δ17O ≥ 0‰, the latter being a major component of chondrules and similar to the majority of crystalline silicates recovered from comet Wild 2.
Copyright Elsevier

The correlation between Mg# [= MgO / (MgO + FeO) mol %] and Δ17O values of the samples defines an intermediate trend between those of CM chondrite chondrules and comet Wild 2 samples. Assuming that the CM chondrites, Tagish Lake meteorite, and comet Wild 2 represent C-type asteroids, D-type asteroids, and Kuiper belt objects, respectively, the results of this study indicate that type II chondrules with Δ17O ≥ 0‰ formed at a location much farther out than that where the Tagish Lake meteorite parent body accreted, more than 3.1 million years after the CAI formation assuming homogeneous distribution of 26Al in the early Solar System (Tenner et al., 2019). These two aspects, namely the broad range of heliocentric distance and the prolonged period of chondrule formation, are important constraints when considering appropriate mechanisms of chondrule formation in the protoplanetary disk.

¹A.Kar,¹A.K.Sen,²R.Gupta
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114211]
¹Department of Physics, Assam University, Silchar 788011, India
²IUCAA, Ganeshkhind, Pune 411007, India
Copyright Elsevier

Context:
Numerous minor bodies of our solar system are covered by loosely bound dust particles; these layers are called regolith. Light scattered by regolith surfaces is a function of their bulk porosity, of the sizes, shapes, structures and compositions of the constituent particles.

Aims:
To increase our data base, the present work is an extension of our previous work by Kar et al. (2016), where we reported light scattering data for regolith surfaces with different porosities, sizes, and composition of the particles (from very low to moderate absorption). The new samples have larger particles with moderate to high absorption, three originate from industry, and three are natural (among them a mixture of two previously studied samples).

Methods:
The samples were prepared with different bulk porosities. Photometric phase curves were built for two different geometrical configurations. The light source was a He-Ne laser at 632.8 nm. The phase angle () covered for the first configuration is from 45 to 126° and for the second configuration it is from 45 to 108°, in steps of 9 and 4.5° respectively. We maintained incident angle ()= emergent angle () for the first configuration and , while varying for the second configuration. The experimental data were fitted successfully to the semi-empirical model proposed by Hapke (2008) and interpreted in terms of the porosities and sizes of the particles. The albedo values obtained from the model for two samples are compared to those calculated directly from Mie theory.

Results:
The successful fit by the model is confirmed just as the increase of reflectivity with the decrease of porosities for a given composition and particle size. Further, it was observed that reflectivity increases with the decrease in particle size for a given composition.

Finally, we have tested that for corundum and silicon carbide samples with a and particle sizes ( respectively), the best fitted albedo () values that can be obtained from Hapke model, match very well with those calculated directly by Mie Theory. This also re-validated our approach adopted in the present work.

¹Anicia Arredondo,¹Humberto Campins,²Noemi Pinilla-Alonso,^3,4Juliade León,^5,3Vania Lorenzi,^3,6David Morate
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114210]
¹Physics Department, University of Central Florida, P.O. Box 162385, Orlando, FL 32816, USA
²Florida Space Institute, University of Central Florida, Orlando, FL 32816, USA
³Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁴Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁵Fundación Galileo Galilei – INAF, La Palma (TF), Spain
⁶Observatório Nacional, Coordenação de Astronomia e Astrofísica, 20921-400 Rio de Janeiro, Brazil
Copyright Elsevier

We present NIR spectra of 19 asteroids in the Sulamitis family as part of our survey of primitive inner belt asteroid families. The spectra were obtained with NASA’s Infrared Telescope Facility and the Telescopio Nazionale Galileo between January 2017 and February 2020. We find spectral homogeneity in our sample despite the diversity within the family observed at visible wavelengths. The average Sulamitis spectrum is flat with a spectral slope of 0.89 ± 0.26%/1000 Å between 0.95 and 2.3 μm. We show that the Sulamitis family is spectrally similar to other inner belt families in the NIR, despite differences between families seen in the visible wavelength range. We also compare our obtained spectra with asteroids (101955) Bennu and (162173) Ryugu to show that the Sulamitis family is a plausible source of Ryugu.

¹Bazhan, I.S.,^2,3Litasov, K.D.,⁴Badyukov, D.D.
Russian Geology and Geophysics 61, 241-249 Link to Article [DOI: 10.15372/RGG2019072]
¹V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russian Federation
²Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, Kaluzhskoe shosse 14, Troitsk, Moscow, 108840, Russian Federation
³Fersman Mineralogical Museum, Russian Academy of Sciences, Leninsky pr. 18/2, Moscow, 119071, Russian Federation
⁴Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russian Federation

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Xiao-DuanZou et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114183]
¹Planetary Science Institute, Tucson, AZ, USA
Copyright Elsevier

NASA’s OSIRIS-REx spacecraft arrived at its sampling target, asteroid (101955) Bennu, in December 2018 and started a series of global observation campaigns. Here we investigate the global photometric properties of Bennu as observed by the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS) over the time period December 9, 2018, to September 26, 2019. In this study we used observations obtained over wavelengths ranging from 0.4 to 3.7 μm, with a solar phase angle range of 5.3° to 132.6°. Our aim is to characterize the global average disk-resolved photometric properties of Bennu with multiple models. The best-fit model is a McEwen model with an exponential phase function and an exponential polynomial partition function. We use this model to correct the OVIRS spectra of Bennu to a standard reference viewing and illumination geometry at visible to infrared wavelengths for the purposes of global spectral mapping. We derive a bolometric Bond albedo map in which Bennu’s surface values range from 0.021 to 0.027. We find a phase reddening effect, and our model is effective at removing this phase reddening. Our average model albedo shows a blueish spectrum with a > 10% absorption feature centered at 2.74 μm. Of all comparisons with previously visited asteroids and comets, only 28P/Neujmin, 2P/Encke, and (162173) Ryugu are darker than Bennu. We find that Bennu is a few percent brighter than Ryugu in the wavelengths respectively observed by the OSIRIS-REx and Hayabusa2 missions (from 0.48 to 0.86 μm). We also compare our spectroscopic photometry of Bennu with the OSIRIS-REx imaging photometry and with ground-based predictions.

^1,2,3Gu, L.,^2,4Wang, N.,^1,2,3Tang, X.,^2,3,5,6Changela, H.G.
Scanning 2020, 8406917 Link to Article [DOI: 10.1155/2020/8406917]
¹Electron Microscopy Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
²Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
³Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing, 10029, China
⁴University of Chinese Academy of Sciences, Beijing, China
⁵Qian Xuesen Laboratory of Space Technology, Chinese Academy of Space Technology, Beijing, China
⁶Department of Earth and Planetary Science, University of New Mexico, New Mexico, United States

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2D.N.DellaGiustina et al. (>10)
Science 370, eabc3660 Link to Article [DOI: 10.1126/science.abc3660]
¹Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA.
²Department of Geosciences, University of Arizona, Tucson, AZ, USA.
Reprinted with permission from AAAS

Visible-wavelength color and reflectance provide information about the geologic history of planetary surfaces. Here we present multispectral images (0.44 to 0.89 micrometers) of near-Earth asteroid (101955) Bennu. The surface has variable colors overlain on a moderately blue global terrain. Two primary boulder types are distinguishable by their reflectance and texture. Space weathering of Bennu surface materials does not simply progress from red to blue (or vice versa). Instead, freshly exposed, redder surfaces initially brighten in the near-ultraviolet region (i.e., become bluer at shorter wavelengths), then brighten in the visible to near-infrared region, leading to Bennu’s moderately blue average color. Craters indicate that the time scale of these color changes is ~105 years. We attribute the reflectance and color variation to a combination of primordial heterogeneity and varying exposure ages.

^1,2H.H.Kaplan et al. (>10)
Science 370, eabc3557 Link to Article [DOI: 10.1126/science.abc3557]
¹NASA Goddard Space Flight Center, Greenbelt, MD, USA.
²Southwest Research Institute, Boulder, CO, USA.
Reprinted with permission from AAAS

The composition of asteroids and their connection to meteorites provide insight into geologic processes that occurred in the early Solar System. We present spectra of the Nightingale crater region on near-Earth asteroid Bennu with a distinct infrared absorption around 3.4 micrometers. Corresponding images of boulders show centimeters-thick, roughly meter-long bright veins. We interpret the veins as being composed of carbonates, similar to those found in aqueously altered carbonaceous chondrite meteorites. If the veins on Bennu are carbonates, fluid flow and hydrothermal deposition on Bennu’s parent body would have occurred on kilometer scales for thousands to millions of years. This suggests large-scale, open-system hydrothermal alteration of carbonaceous asteroids in the early Solar System.

¹Amy A. Simon et al. (>10)
Science 370, eabc3522 Link to Article [DOI: 10.1126/science.abc3522]
¹Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA.
Reprinted with Permission from AAAS

Asteroid (101955) Bennu is a dark asteroid on an Earth-crossing orbit that is thought to have assembled from the fragments of an ancient collision. We use spatially resolved visible and near-infrared spectra of Bennu to investigate its surface properties and composition. In addition to a hydrated phyllosilicate band, we detect a ubiquitous 3.4-micrometer absorption feature, which we attribute to a mix of organic and carbonate materials. The shape and depth of this absorption feature vary across Bennu’s surface, spanning the range seen among similar main-belt asteroids. The distribution of the absorption feature does not correlate with temperature, reflectance, spectral slope, or hydrated minerals, although some of those characteristics correlate with each other. The deepest 3.4-micrometer absorptions occur on individual boulders. The variations may be due to differences in abundance, recent exposure, or space weathering.

¹Tamilarasan Subramani,¹Kristina Lilova,¹Mykola Abramchuk,¹Kurt D. Leinenweber,¹Alexandra Navrotsky
Proceedings of the National Academy of Sciences of the United States of America Link to Article [DOI:
https://doi.org/10.1073/pnas.2017312117]
¹School of Molecular Sciences and Center for Materials of the Universe, Arizona State University, Tempe, AZ 85281

Iron sulfide minerals are widespread on Earth and likely in planetary bodies in and beyond our solar system. Using measured enthalpies of formation for three magnetic iron sulfide phases: bulk and nanophase Fe3S4 spinel (greigite), and its high-pressure monoclinic phase, we show that greigite is a stable phase in the Fe–S phase diagram at ambient temperature. The thermodynamic stability and low surface energy of greigite supports the common occurrence of fine-grained Fe3S4 in many anoxic terrestrial settings. The high-pressure monoclinic phase, thermodynamically metastable below about 3 GPa, shows a calculated negative P-T slope for its formation from the spinel. The stability of these three phases suggests their potential existence on Mercury and their magnetism may contribute to its present magnetic field.