1,2Pignatale, F.C.,2Charnoz, S.,2Chaussidon, M.,1Jacquet, E.
Proceedings of the International Astronomical Union 2019, 137-140 Link to Article [DOI: 10.1017/S1743921318008311]
1Muséum National d’Histoire Naturelle, UMR 7590, CP52, 57 rue Cuvier, Paris, 75005, France
2Institut de Physique du Globe de Paris (IPGP), 1 rue Jussieu, Paris, 75005, France
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1,2J.N.Rasera,1J.J.Cilliers,2J.-A.Lamamy,1K.Hadler
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2020.104879]
1Earth Science and Engineering, Imperial College London, SW7 2AZ, United Kingdom
2Ispace Europe S.A., Rue de l’Industrie 5, L-1811, Ville de Luxembourg, Luxembourg
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1Young, E.D.,1Elmegreen, B.G.,1Tóth,L.V.,1Güdel, M.
Proceedings of the International Astronomical Union
2019,70-77 Link to Article [DOI: 10.1017/S1743921319001777]
1Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, United States
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1Fujimoto, Y.,1Krumholz, M.R.,2Tachibana, S.,1Elmegreen, B.G.,Tóth, L.V.,Güdel, M.
Proceedings of the International Astronomical Union 2019, 83-86 Link to Article [DOI: 10.1017/S1743921319001534]
1Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
2UTokyo Organization for Planetary and Space Science (UTOPS), University of Tokyo, 7-3-1 Hongo, Tokyo, 113-0033, Japan
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1J.F.Brossier,1M.S.Gilmore,1K.Toner
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.113693]
1Wesleyan University, Department of Earth and Environmental Sciences, Planetary Sciences Group, 265 Church St., Middletown, CT 06459, USA
Copyright Elsevier
Multiple studies reveal that most of Venus highlands exhibit anomalously high radar reflectivity and low radar emissivity relative to the lowlands. This phenomenon is thought to be the result of atmosphere-surface interactions in the highlands, due to lower temperatures. These reactions are a function of rock composition, atmospheric composition, and degree of weathering. We examine the Magellan radar emissivity, altimetry and SAR data for all major volcanoes and coronae on Venus. We characterize and classify edifices according to the pattern of the variation of radar emissivity with altitude. The volcanic highlands can be classified into 7 distinct patterns of emissivity that correspond to at least 3 discrete types of mineralogy based on the altitude (temperature) of the emissivity anomalies. The majority of emissivity anomalies support the hypothesis of a weathering phenomenon at high altitude (>6053 km), but we also find strong emissivity anomalies at lower altitudes that correspond spatially to individual lava flows, indicating variations in mineralogy within an evolving volcanic system. The emissivity signature of tallest volcanoes on Venus are consistent with the presence of ferroelectric minerals in their rocks, while volcanic edifices in western Ishtar Terra and eastern Aphrodite Terra are consistent with the presence of semiconductor minerals. Sapas Mons and Pavlova Corona are also consistent with ferroelectrics, but at a different Curie temperature than the other volcanoes in Atla Regio. The spatial distribution of radar emissivity classes correlates to different geologic settings indicating that different mantle source regions (deep/shallow plumes, and possible convergence zones) may contribute to differences in mineralogy for the studied edifices. Finally, we show that the emissivity signatures of Idunn, Maat and other volcanic edifices are consistent with relatively fresh and unweathered rocks, indicating recent or possibly current volcanism on Venus.
1Munan Gong (龚 慕南),2Xiaochen Zheng (郑 晓晨),2,3,4Douglas N. C. Lin (林潮),1Kedron Silsbee,5Clement Baruteau,1Shude Mao (毛 淑德)
The Astrophysical Journal 883, 164 Link to Article [DOI
https://doi.org/10.3847/1538-4357/ab3e70]
1Max-Planck Institute for Extraterrestrial Physics, Garching by Munich, D-85748, Germany
2Department of Astronomy and Center for Astrophysics, Tsinghua University, Beijing 10086, People’s Republic of China
3Institute for Advanced Studies, Tsinghua University, Beijing 10086, People’s Republic of China
4Department of Astronomy and Astrophysics, University of California Santa Cruz, Santa Cruz, CA 95064, USA
5Institut de Recherche en Astrophysique et Planétologie (IRAP), 14 avenue Edouard Belin, F-31400 Toulouse, France
Chondrules are silicate spheroids found in meteorites, and they serve as important fossil records of the early solar system. In order to form chondrules, chondrule precursors must be heated to temperatures much higher than the typical conditions in the current asteroid belt. One proposed mechanism for chondrule heating is the passage through bow shocks of highly eccentric planetesimals in the protoplanetary disk in the early solar system. However, it is difficult for planetesimals to gain and maintain such high eccentricities. In this paper, we present a new scenario in which planetesimals in the asteroid belt region are excited to high eccentricities by the Jovian sweeping secular resonance in a depleting disk, leading to efficient formation of chondrules. We study the orbital evolution of planetesimals in the disk using semi-analytic models and numerical simulations. We investigate the dependence of eccentricity excitation on the planetesimal’s size, as well as the physical environment and the probability for chondrule formation. We find that 50–2000 km planetesimals can obtain eccentricities larger than 0.6 and cause effective chondrule heating. Most chondrules form in high-velocity shocks, in low-density gas, and in the inner disk. The fraction of chondrule precursors that become chondrules is about 4%–9% between 1.5 and 3 au. Our model implies that the disk depletion timescale is τ dep ≈ 1 Myr, comparable to the age spread of chondrules, and that Jupiter formed before chondrules, no more than 0.7 Myr after the formation of calcium aluminum inclusions.
1,2Fei Dai,2,4Kento Masuda,2Joshua N. Winn,3Li Zeng
The Astrophysical Journal 883, 79 Link to Article [DOI
https://doi.org/10.3847/1538-4357/ab3a3b]
1Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
2Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
3Department of Earth & Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA
4NASA Sagan Fellow.
Terrestrial planets have been found orbiting Sun-like stars with extremely short periods—some as short as 4 hr. These “ultra-short-period planets” or “hot Earths” are so strongly irradiated that any initial H/He atmosphere has probably been lost to photoevaporation. As such, the sample of hot Earths may give us a glimpse at the rocky cores that are often enshrouded by thick H/He envelopes on wider-orbiting planets. However, the mass and radius measurements of hot Earths have been derived from a hodgepodge of different modeling approaches, and include several cases of contradictory results. Here, we perform a homogeneous analysis of the complete sample of 11 known hot Earths with an insolation exceeding 650 times that of the Earth. We combine all available data for each planet, incorporate parallax information from Gaia to improve the stellar and planetary parameters, and use Gaussian process regression to account for correlated noise in the radial-velocity data. The homogeneous analysis leads to a smaller dispersion in the apparent composition of hot Earths, although there does still appear to be some intrinsic dispersion. Most of the planets are consistent with an Earth-like composition (35% iron and 65% rock), but two planets (K2-141b and K2-229b) show evidence for a higher iron fraction, and one planet (55 Cnc e) has either a very low iron fraction or an envelope of low-density volatiles. All of the planets are less massive than 8 M ⊕, despite the selection bias toward more massive planets, suggesting that 8 M ⊕ is the critical mass for runaway accretion.
1Tetsuya Yokoyama,1,2Yuichiro Nagai,1,2Ryota Fukai,2Takafumi Hirata
The Astrophysical Journal 883, 62 Link to Article [DOI
https://doi.org/10.3847/1538-4357/ab39e7]
1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
2Geochemical Research Center, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
New high-precision Mo isotopic data were obtained for 10 iron meteorites and two carbonaceous, five ordinary, and two rumuruti chondrites. A clear isotopic dichotomy is observed in μ i Mo−μ 94Mo diagrams between the CC meteorites (carbonaceous chondrites and IVB irons) and other noncarbonaceous (NC) meteorites. The Mo isotope variabilities within the CC meteorites can indicate either s-process matter distributed heterogeneously throughout various chondritic components in the different outer solar system materials or that generated by a local parent-body processing. In contrast, the presence of two end-member components for the Mo isotope composition, that is, NC-A and NC-B, was suggested in the NC reservoir. The NC-B component represents the remaining counterpart of the gaseous source reservoir for type B calcium-aluminum-rich inclusions, which was presumably formed via thermal processing that destroyed r-process-rich carriers. Two models were proposed to consider the observed Mo isotope variability among the NCs. In model 1, the NC-A reservoir was formed closer to the Sun than the NC-B reservoir by another thermal processing that destroyed s-process-depleted phases. The Mo isotopic composition of the NC region changed via outward motion of particles from the two reservoirs, resulting in a gradual change from NC-A- to NC-B-like components as a function of the heliocentric distance. In model 2, the Mo isotopic composition in individual NCs is controlled by the amount of metal and matrix-like material that is removed from and added to the NC-B reservoir. Such a fractionation process most likely occurred locally in time and/or space in the inner solar system.
1Honglei Lin,2Rui Xu,1Wei Yang,1Yangting Lin,1Yong Wei,1Sen Hu,2Zhiping He,3Le Qiao,1Weixing Wan
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2019JE006076]
1Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
2Key Laboratory of Space Active Opto‐Electronics Technology, Shanghai
Institute of Technical Physics, Chinese Academy of Sciences, Shanghai, China
3Shandong Provincial Key Laboratory of Optical Astronomy and Solar‐Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, China
Published by arrangement with John Wiley & Sons
China’s Chang’E‐4 (CE‐4) mission successfully landed in Von Kármán crater within South Pole‐Aitken basin of the Moon. The Visible and Near‐Infrared Imaging Spectrometer (VNIS) on board Yutu‐2 rover investigated the photometric properties of lunar regolith. Seven VNIS measurements were conducted on a small lunar surface with a diameter <5 m by the rover rotating at the center, with the phase angles from 39.6 to 97.1° obtained in the similar observational geometry of solar altitude and observation angle. The phase function, which varies in different wavelength, is derived using a third‐order polynomial fitting, in combination with the calibration and comparison of orbital/in situ VNIS data at the Chang’E‐4 landing site and the same regions. After the photometrical correction of the spectra with the phase function, the derived FeO contents and optical maturity parameters of the regolith reduce much of their deviations, which is consistent with the homogeneity of the regolith and hence demonstrates the significance of the photometric correction on the VNIS spectra.
1S. A. Singerling,1A. J. Brearley
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13450]
1Department of Earth & Planetary Sciences, University of New Mexico, MSC‐03 2040, Albuquerque, New Mexico, 87131 USA
Published by arrangement with John Wiley & Sons
The presence of primary iron sulfides that appear to be aqueously altered in CM and CR carbonaceous chondrites provides the potential to study the effects and, by extension, the conditions of aqueous alteration. In this work, we have used SEM, TEM, and EPMA techniques to characterize primary sulfides that show evidence of secondary alteration. The alteration styles consist of primary pyrrhotite altering to secondary pentlandite (CMs only), magnetite (CMs and CRs), and phyllosilicates (CMs only) in grains that initially formed by crystallization from immiscible sulfide melts in chondrules (pyrrhotite‐pentlandite intergrowth [PPI] grains). Textural, microstructural, and compositional data from altered sulfides in a suite of CM and CR chondrites have been used to constrain the conditions of alteration of these grains and determine their alteration mechanisms. This work shows that the PPI grains exhibit two styles of alteration—one to form porous pyrrhotite‐pentlandite (3P) grains by dissolution of precursor PPI grain pyrrhotite and subsequent secondary pentlandite precipitation (CMs only), and the other to form the altered PPI grains by pseudomorphic replacement of primary pyrrhotite by magnetite (CMs and CRs) or phyllosilicates (CMs only). The range of alteration textures and products is the result of differences in conditions of alteration due to the role of microchemical environments and/or brecciation. Our observations show that primary sulfides are sensitive indicators of aqueous alteration processes in CM and CR chondrites.
Cosmochemistry Papers 