¹M. Martínez-Paredes,²O. González-Martín,²D. Esparza-Arredondo,¹M. Kim,³A. Alonso-Herrero,⁴Y. Krongold,¹T. Hoang,^5,6C. Ramos Almeida,⁷I. Aretxaga,⁴D. Dultzin,¹J. Hodgson
The Astrophysical Journal 890, 152 Link to Article [DOI
https://doi.org/10.3847/1538-4357/ab6732]
¹Korea Astronomy and Space Science Institute 776, Daedeokdae-ro, Yuseong-gu, Daejeon, Republic of Korea (34055
²Instituto de Radioastronomía y Astrofísica UNAM Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán, Mexico
³Centro de Astrobiología, CSIC-INTA, ESAC Campus, E-28692 Villanueva de la Cañada, Madrid, Spain
⁴Instituto de Astronomía UNAM, México, CDMX., C.P. 04510, Mexico
⁵Instituto de Astrofísica de Canarias (IAC), E-38205 La Laguna, Tenerife, Spain
⁶Departamento de Astrofísica, Universidad de La Laguna (ULL), E-38206 La Laguna, Tenerife, Spain
⁷Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), Luis Enrrique Erro 1, Sta. Ma. Tonantzintla, Puebla, Mexico

We measure the 10 and 18 μm silicate features in a sample of 67 local (z < 0.1) type 1 active galactic nuclei (AGN) with available Spitzer spectra dominated by nonstellar processes. We find that the 10 μm silicate feature peaks at with a strength (Si _p  = ln f _p (spectrum)/f _p (continuum)) of , while the 18 μm one peaks at with a strength of . We select from this sample sources with the strongest 10 μm silicate strength (, 10 objects). We carry out a detailed modeling of the infrared spectrometer/Spitzer spectra by comparing several models that assume different geometries and dust composition: a smooth torus model, two clumpy torus models, a two-phase medium torus model, and a disk+outflow clumpy model. We find that the silicate features are well modeled by the clumpy model of Nenkova et al., and among all models, those including outflows and complex dust composition are the best. We note that even in AGN-dominated galaxies, it is usually necessary to add stellar contributions to reproduce the emission at the shortest wavelengths.

¹Norbert Schorghofer
The Astrophysical Journal 890, 49 Link to Article [DOI
https://doi.org/10.3847/1538-4357/ab612f]
¹Planetary Science Institute, Tucson, AZ 85719, USA

The possibility of liquid water on present-day Mars has been debated for half a century. Melting is physically difficult under Martian environmental conditions, because with the total pressure of the atmosphere near the triple point pressure of water, evaporative cooling of ice is high near the melting point. Here, a suite of quantitative models is used to investigate whether melting of seasonal water frost can occur on present-day Mars. An updated and generalized parameterization is derived for the turbulent convective heat flux that results from the buoyancy of water vapor. A three-dimensional surface energy balance model is used to calculate surface temperatures; it includes terrain shadowing, self heating, and subsurface conduction. Protruding topography creates locations that experience a rapid transition from conditions where water frost accumulates to high solar energy input. Beyond the pole-facing side of a boulder, CO2 and frost can accumulate seasonally, and once the Sun reemerges and the CO2 frost disappears, the water frost is heated to near melting temperature within one or two sols. Dust contained in the CO2 frost facilitates the formation of a protective sublimation lag. Temperatures within about 10 K of the melting point are reached within one or two sols after the end of water frost accumulation. For expected sublimation lag thicknesses, evaporative cooling is not significantly reduced. Overall, melting of pure water ice is not expected under present-day Mars conditions. However, at temperatures that are readily reached, seasonal water frost can melt on a salt-rich substrate. Hence, crocus melting behind boulders can lead to the formation of brines under present-day Mars conditions.

^1,2Tomohiro Usui,³Ken-ichi Bajo,⁴Wataru Fujiya,⁵Yoshihiro Furukawa,¹Mizuho Koike,⁶Yayoi N. Miura,¹Haruna Sugahara,^1,7Shogo Tachibana,⁸Yoshinori Takano,^1,3Kiyoshi Kuramoto
Space Science Reviews 216, 49 Link to Article [DOI
https://doi.org/10.1007/s11214-020-00668-9]
¹Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, Kanagawa, 252-5210, Japan
²Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8550, Japan
³Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University, N10W8 Kita-ku, Sapporo, 060-0810, Japan
⁴Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki, 310-8512, Japan
⁵Department of Earth Science, Tohoku University, 6-3 Aza-aoba, Aramaki, Aoba-ku, Sendai, 980-8578, Japan
⁶Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-0032, Japan
⁷UTOPS, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
⁸Biogeochemistry Research Center, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, 237-0061, Japan

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¹Monica M. Grady
Space Science Reviews 216, 51 Link to Article [DOI
https://doi.org/10.1007/s11214-020-00676-9]
¹School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK

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¹Hiroshi Kikuchi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113997]
¹Institute of Space and Astronautical Science, JAXA, Sagamihara 252-5210, Japan
Copyright Elsevier

The spatial distribution pattern of ejecta from an impact crater on the surface of a body in space holds clues to understanding the ejecta launch conditions, the crater excavation process, and the dynamical environment. In particular, focusing on re-impact sites from larger or deeper craters on the surface is important, as they tend to preserve much of the original information. The surface of the Martian satellite Phobos is spectrally divided into red and blue units. The former are globally distributed, while the blue units have been observed inside and outside the Stickney crater—the largest and deepest crater on Phobos. Outside the crater, the blue units are concentrated in the region from the south to the west (south-west blue units) and in the region east of the crater (east blue units). Several models can explain the concentration of east blue units. However, the mode of formation of south-west blue units is still unknown, despite its vast area. We proposed that the combination of ejecta from Stickney and Limtoc (a crater located on the floor of Stickney) contributed to the formation of the blue units. We tested the model using ballistic simulations incorporating, an updated shape model with randomly generated ejecta velocities, different values of orbital radii to Mars, and various launching velocities, to track the emplacement of the ejecta particles. The results showed that the distribution of the two blue units is recreated when the combined re-impact sites of ejecta from Stickney and Limtoc have orbital radius (X_Ph) values of X_Ph > 3.34 R_M and X_Ph < 3.04 R_M, respectively. The observations and the results suggest that Phobos comprises an inner blue layer covered by red materials globally and locally excavated blue materials, and the age of the Stickney crater may be sufficiently old to be estimated from the crater densities.

¹Katsuhito Ohtsuka et al. (>10)
Planetary ans Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.104940]
¹Tokyo Meteor Network, 1–27–5 Daisawa, Setagaya-ku, Tokyo, 155–0032, Japan

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¹J.Gattacceca,²L.Bonal,¹C.Sonzogni,¹J.Longerey
Earth and Planetary Science 547, 116467 Link to Article [https://doi.org/10.1016/j.epsl.2020.116467]
¹CNRS, Aix Marseille Univ, IRD, INRAE, CEREGE, Aix-en-Provence, France
²Institut de Planétologie et d’Astrophysique de Grenoble, Université Grenoble Alpes, CNRS CNES, 38000 Grenoble, France
Copyright Elsevier

CV chondrites are one of the most studied group of carbonaceous chondrites. Based on a number of mineralogical features, they have been divided into three sub-groups: CVOxA, CVOxB, and CVRed. These sub-groups are classically interpreted as coming from a single parent body, with a common protolith affected by significant parent body fluid-assisted metasomatism occurring at different temperatures and/or redox conditions. In this work, we studied a set of 53 CV chondrites. We classified them into the three sub-groups, measured their apparent chondrule sizes and their matrix modal abundance. We measured the triple oxygen isotopic composition for 17 of them. The distributions of chondrule size and matrix abundances in CVOxA and CVOxB cannot be statistically distinguished. Conversely, CVRed and CVOx have distinct distributions. These two robust and simple petrographic indicators combined with the previous knowledge of the peak metamorphic temperatures experienced by these meteorites show that CVOx and CVRed originate from two distinct parent bodies. On the other hand, CVOxA and CVOxB likely originate from the same parent body, with CVOxA representing deeper, more metamorphosed levels. For clarification of the chondrite classification scheme, in which one group should ultimately represent a single parent body, we propose to divide the CV group into two proper groups (and not subgroups as in the current scheme), keeping the names CVRed and CVOx. These two groups can be readily separated by estimating the average nickel content of their sulfides.

¹Romain Tartèse,^2,3Mahesh Anand,⁴Jérôme Gattacceca,¹Katherine H. Joy,²James I. Mortimer,¹John F. Pernet-Fisher,³Sara Russell,⁵Joshua F. Snape,⁶Benjamin P. Weiss
Space Science Reviews 215, 54 Link to Article [DOI
https://doi.org/10.1007/s11214-019-0622-x]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester, M13 9PL, UK
²Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
³Department of Earth Sciences, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK
⁴CNRS, Aix-Marseille Univ, IRD, Coll France, INRA, CEREGE, Aix-en-Provence, France
⁵Faculty of Sciences, Department of Earth Sciences, Vrije Universiteit, Amsterdam, The Netherlands
⁶Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA

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¹Zita Martins,²Queenie Hoi Shan Chan,³Lydie Bonal,⁴Ashley King,⁵Hikaru Yabuta
Space Science Reviews 216, 54 Link to Article [DOI
https://doi.org/10.1007/s11214-020-00679-6]
¹Centro de Química Estrutural, Departamento de Engenharia Química, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais 1, 1049-001, Lisboa, Portugal
²Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
³Institut de Planétologie et d’Astrophysique de Grenoble, Univ. Grenoble Alpes, CNRS, CNES, 38000, Grenoble, France
⁴The Natural History Museum, Cromwell Road, London, SW7 5BD, UK
⁵Department of Earth and Planetary Systems Science, Hiroshima University, 1-3-1 Kagamiyama, Hiroshima, 739-8526, Japan

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¹Kanta Fukimoto,¹Masaaki Miyahara,²Takeshi Sakai,²Hiroaki Ohfuji,³Naotaka Tomioka,⁴Yu Kodama,⁵Eiji Ohtani,^6,7Akira Yamaguchi
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13543]
¹Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi‐Hiroshima, 739‐8526 Japan
²Geodynamics Research Center, Ehime University, Matsuyama, 790‐8577 Japan
³Kochi Institute for Core Sample Research, Japan Agency for Marine‐Earth Science and Technology (JAMSTEC), Nankoku, Kochi, 783‐8502 Japan
⁴Marine Works Japan, Nankoku, Kochi, 783‐8502 Japan
⁵Department of Earth Sciences, Graduate School of Science, Tohoku University, Sendai, 980‐8578 Japan
⁶National Institute of Polar Research, Tokyo, 190‐8518 Japan
⁷Department of Polar Science, School of Multidisciplinary Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, 190‐8518 Japan
Published by arrangement with John Wiley & Son

We investigated the back‐transformation mechanisms of ringwoodite and majorite occurring in a shock‐melt vein (SMV) of the Yamato 75267 H6 ordinary chondrite during atmospheric entry heating. Ringwoodite and majorite in the shock melt near the fusion crust have back‐transformed into olivine and enstatite, respectively. Ringwoodite (Fa_~18) occurs in the SMV as a fine‐grained polycrystalline assemblage. Approaching the fusion crust, fine‐grained polycrystalline olivine becomes dominant instead of ringwoodite. The back‐transformation from ringwoodite to olivine proceeds by incoherent nucleation and by an interface‐controlled growth mechanism: nucleation occurs on the grain boundaries of ringwoodite, and subsequently olivine grains grow. Majorite (Fs_16–17En_82–83Wo₁) occurs in the SMV as a fine‐grained polycrystalline assemblage. Approaching the fusion crust, the majorite grains become vitrified. Approaching the fusion crust even more, clino/orthoenstatite grains occur in the vitrified majorite. The back‐transformation from majorite to enstatite is initiated by the vitrification, and growth continues by the subsequent nucleation in the vitrified majorite.