Evidence for Asteroid Scattering and Distal Solar System Solids From Meteorite Paleomagnetism

1,2James F. J. Bryson,2Benjamin P. Weiss,2Eduardo A. Lima,3Jérôme Gattacceca,4William S. Cassata
The Astrophysical Journal 892, 126 Link to Article [DOI
1Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
2Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
3CNRS, Aix Marseille Université, IRD, Coll France, INRA, CEREGE, Aix-en-Provence, France
4Lawrence Livermore National Laboratory, Livermore, CA 94550, USA

Asteroid-sized bodies are predicted to have been scattered throughout the solar system following gravitational interactions with the giant planets. This process could have delivered water-rich small bodies to the inner solar system. However, evidence from the meteorite record supporting this scattering is limited due to difficulties in recovering the formation distance of meteorite parent bodies from laboratory measurements. Moreover, ancient millimeter-sized solids that formed in the inner solar system (calcium–aluminum-rich inclusions (CAIs) and chondrules) have also been proposed to have migrated throughout the solar system, which could have been key to their survival. Our understanding of the driving mechanisms, distances, and timings involved in this motion is also restricted for the same reasons. Here, we address these limitations by recovering the formation distance of the parent asteroid of the Tagish Lake meteorite from measurements of its natural remanent magnetization. We find that this meteorite experienced an ancient field intensity <0.15 μT. Accounting for the average effect of a tilted parent body rotation axis and possible uncertainties associated with the remanence acquisition mechanism, this result argues that the Tagish Lake parent body formed at >8–13 au, suggesting this body originates from the distal solar system. Tagish Lake came to Earth from the asteroid belt which, combined with our recovered formation distance, suggests that some small bodies traveled large distances throughout the solar system. Moreover, Tagish Lake contains CAIs and chondrules, indicating that these solids were capable of traveling to the distal solar system within just a few million years.

Separate Silicate and Carbonaceous Solids Formed from Mixed Atomic and Molecular Species Diffusing in Neon Ice

1Gaël Rouillé,1Cornelia Jäger,2Thomas Henning
The Astrophysical Journal 892,96 Link to Article [DOI
1Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany
2Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany

The formation and growth of refractory matter on pre-existing interstellar dust grain surfaces was studied experimentally by annealing neon-ice matrices in which potential precursors of silicate grains (Mg and Fe atoms, SiO and SiO2 molecules) and of solid carbon (C n molecules, n = 2–10) were initially isolated. Other molecules, mainly O3, CO, CO2, C3O, and H2O, were embedded at the same time in the matrices. The annealing procedure caused the cold dopants to diffuse and interact in the neon ice. Monitoring the procedure in situ with infrared spectroscopy revealed the disappearance of the silicon oxide and carbon molecules at temperatures lower than 13 K, and the rise of the Si–O stretching band of silicates. Ex situ electron microscopy confirmed the formation of silicate grains and showed that their structure was amorphous. It also showed that amorphous carbon matter was formed simultaneously next to the silicate grains, the two materials being chemically separated. The results of the experiments support the hypothesis that grains of complex silicates and of carbonaceous materials are reformed in the cold interstellar medium, as suggested by astronomical observations and evolution models of cosmic dust masses. Moreover, they show that the potential precursors of one material do not combine with those of the other at cryogenic temperatures, providing us with a clue as to the separation of silicates and carbon in interstellar grains.

Orbital Properties and Gravitational-wave Signatures of Strangelet Crystal Planets

1Joás Zapata,1Rodrigo Negreiros
The Astrophysical Journal 892, 67 Link to Article [DOI
1Instituto de Física, Universidade Federal Fluminense, Av. Gal. Milton Tavares S/N, Niterói, Brazil

In this paper we consider the possibility that strange quark matter (SQM) may manifest in the form of strangelet crystal planets. These planet-like objects are made up of nuggets of SQM, organized in a crystalline structure. We consider the so-called strange matter hypothesis proposed by Bodmer, Witten, and Terazawa, in that SQM may be the absolutely stable state of matter. In this context, we analyze planets made up entirely of strangelets arranged in a crystal lattice. Furthermore, we propose that a solar system with a host compact star may be orbited by strange crystal planets. Under this assumption we calculate the relevant quantities that could potentially be observable, such as the planetary tidal disruption radius, and the gravitational-wave signals that may arise from potential star–planet merger events. Our results show that strangelet crystal planets could potentially be used as an indicator for the existence of SQM.

Dynamic Potential Sputtering of Lunar Analog Material by Solar Wind Ions

1Paul S.Szabo et al. (>10)
The Astrophysical Jounal 891, 100 Link to Article [DOI
1Institute of Applied Physics, TU Wien, Wiedner Hauptstraße 8-10, A-1040 Vienna, Austria

Pyroxenes ((Ca, Mg, Fe, Mn)2Si2O6) belong to the most abundant rock forming minerals that make up the surface of rocky planets and moons. Therefore, sputtering of pyroxenes by solar wind ions has to be considered as a very important process for modifying the surface of planetary bodies. This is increased due to potential sputtering by multiply charged ions; to quantify this effect, sputtering of wollastonite (CaSiO3) by He2+ ions was investigated. Thin films of CaSiO3 deposited on a quartz crystal microbalance were irradiated, allowing precise, in situ, real time sputtering yield measurements. Experimental results were compared with SDTrimSP simulations, which were improved by adapting the used input parameters. On freshly prepared surfaces, He2+ ions show a significant increase in sputtering, as compared to equally fast He+ ions. However, the yield decreases exponentially with fluence, reaching a lower steady state after sputtering of the first few monolayers. Experiments using Ar8+ ions show a similar behavior, which is qualitatively explained by a preferential depletion of surface oxygen due to potential sputtering. A corresponding quantitative model is applied, and the observed potential sputtering behaviors of both He and Ar are reproduced very well. The results of these calculations support the assumption that mainly O atoms are affected by potential sputtering. Based on our findings, we discuss the importance of potential sputtering for the solar wind eroding the lunar surface. Estimated concentration changes and sputtering yields are both in line with previous modeling for other materials, allowing a consistent perspective on the effects of solar wind potential sputtering.

Modeling the Strongest Silicate Emission Features of Local Type 1 AGNs

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
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 ${10.3}_{-0.9}^{+0.7}\,\mu {\rm{m}}$ with a strength (Si p  = ln f p (spectrum)/f p (continuum)) of ${0.11}_{-0.36}^{+0.15}$, while the 18 μm one peaks at ${17.3}_{-0.7}^{+0.4}\,\mu {\rm{m}}$ with a strength of ${0.14}_{-0.06}^{+0.06}$. We select from this sample sources with the strongest 10 μm silicate strength (${\sigma }_{{\mathrm{Si}}_{10\mu {\rm{m}}}}\gt 0.28$, 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.

Mars: Quantitative Evaluation of Crocus Melting behind Boulders

1Norbert Schorghofer
The Astrophysical Journal 890, 49 Link to Article [DOI
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.

The Importance of Phobos Sample Return for Understanding the Mars-Moon System

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
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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Simulating re-impacts from craters at the deepest location of Phobos to generate its blue spectral units

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 (XPh) values of XPh > 3.34 RM and XPh < 3.04 RM, 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.