IDP-like Asteroids Formed Later than 5 Myr After Ca–Al-rich Inclusions

Marc Neveu1,2 and Pierre Vernazza3
Astrophysical Journal 875, 30 Link to Article [DOI: 10.3847/1538-4357/ab0d87 ]
1University of Maryland, 4296 Stadium Dr., College Park, MD 20742, USA
2NASA Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt, MD 20770, USA
3Aix-Marseille Université, CNRS, Laboratoire d’Astrophysique de Marseille, 38 Rue Frederic Joliot Curie, F-13013 Marseille, France

The parent bodies of ordinary chondrites, carbonaceous CM chondrites, and interplanetary dust particles (IDPs) represent most of the mass of the solar system’s small (D ≤ 250 km) bodies. The times of formation of the ordinary and carbonaceous CM chondrite parent bodies have previously been pinpointed, respectively, to ≈2 and 3–4 million years after calcium–aluminum-rich inclusions (CAIs). However, the timing of the formation of IDP parent bodies such as P- and D-type main-belt asteroids and Jupiter Trojans has not been tightly constrained. Here, we show that they formed later than 5–6 million years after CAIs. We use models of their thermal and structural evolution to show that their anhydrous surface composition would otherwise have been lost due to melting and ice-rock differentiation driven by heating from the short-lived radionuclide 26Al. This suggests that IDP-like volatile-rich small bodies may have formed after the gas of the protoplanetary disk dissipated and thus later than the massive cores of the giant planets. It also confirms an intuitive increase in formation times with increased heliocentric distance, and suggests that there may have been a gap in time between the formation of carbonaceous chondrite (chondrule-rich) and IDP (chondrule-poor) parent bodies.

Implications of Philae Magnetometry Measurements at Comet 67P/Churyumov–Gerasimenko for the Nebular Field of the Outer Solar System

John B. Biersteker1, Benjamin P. Weiss1, Philip Heinisch2, David Herčik2, Karl-Heinz Glassmeier2, and Hans-Ulrich Auster2
Astrophysical Journal 875, 39 Link to Article [DOI: 10.3847/1538-4357/ab0f2a ]
1Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139-4307, USA
2Technische Universität Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany

The remanent magnetization of solar system bodies reflects their accretion mechanism, the space environment in which they formed, and their subsequent geological evolution. In particular, it has been suggested that some primitive bodies may have formed large regions of coherent remanent magnetization as a consequence of their accretion in a background magnetic field. Measurements acquired by the Rosetta Magnetometer and Plasma Monitor have shown that comet 67P/Churyumov–Gerasimenko (67P) has a surface magnetic field of less than 0.9 nT. To constrain the spatial scale and intensity of remanent magnetization in 67P, we modeled its magnetic field assuming various characteristic spatial scales of uniform magnetization. We find that for regions of coherent magnetization with ≥10 cm radius, the specific magnetic moment is  lesssim× 10−6 ${\rm{A}}\,{{\rm{m}}}^{2}\,{\mathrm{kg}}^{-1}$. If 67P formed during the lifetime of the solar nebula and has not undergone significant subsequent collisional or aqueous alteration, this very low specific magnetization is inconsistent with its formation from the gentle gravitational collapse of a cloud of millimeter-sized pebbles in a background magnetic field gsim3 μT. Given the evidence from other Rosetta instruments that 67P formed by pebble-pile processes, this would indicate that the nebular magnetic field was lesssim3 μT at 15–45 au from the young Sun. This constraint is consistent with theories of magnetically driven evolution of protoplanetary disks.

Multiple Spiral Arms in Protoplanetary Disks: Linear Theor

Ryan Miranda1 and Roman R. Rafikov1,2
Astrophysical Journal 875, 37 Link to Article [DOI: 10.3847/1538-4357/ab0f9e ]
1Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540, USA
2Centre for Mathematical Sciences, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK

Recent observations of protoplanetary disks, as well as simulations of planet–disk interaction, have suggested that a single planet may excite multiple spiral arms in the disk, in contrast to the previous expectations based on linear theory (predicting a one-armed density wave). We reassess the origin of multiple arms in the framework of linear theory by solving for the global two-dimensional response of a nonbarotropic disk to an orbiting planet. We show that the formation of a secondary arm in the inner disk, at about half of the orbital radius of the planet, is a robust prediction of linear theory. This arm becomes stronger than the primary spiral at several tenths of the orbital radius of the planet. Several additional, weaker spiral arms may also form in the inner disk. On the contrary, a secondary spiral arm is unlikely to form in the outer disk. Our linear calculations, fully accounting for the global behavior of both the phases and amplitudes of perturbations, generally support the recently proposed WKB phase argument for the secondary arm origin (as caused by the intricacy of constructive interference of the azimuthal harmonics of the perturbation at different radii). We provide analytical arguments showing that the process of a single spiral wake splitting up into multiple arms is a generic linear outcome of wave propagation in differentially rotating disks. It is not unique to planet-driven waves and also occurs in linear calculations of spiral wakes freely propagating with no external torques. These results are relevant for understanding formation of multiple rings and gaps in protoplanetary disks.

Jupiter’s Formation in the Vicinity of the Amorphous Ice Snowline

Olivier Mousis1, Thomas Ronnet1,2, and Jonathan I. Lunine3
Astrophysical Journal 875, 9 Link to Article [DOI: 10.3847/1538-4357/ab0a72 ]
1Aix Marseille Université, CNRS, CNES, LAM, Marseille, France
2Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, SE-221 00 Lund, Sweden
3Department of Astronomy, Cornell University, Ithaca, NY 14853, USA

Argon, krypton, xenon, carbon, nitrogen, sulfur, and phosphorus have all been measured and found to be enriched by a quasi uniform factor in the 2–4 range, compared to their protosolar values, in the atmosphere of Jupiter. To elucidate the origin of these volatile enrichments, we investigate the possibility of an inward drift of particles made of amorphous ice and adsorbed volatiles, and their ability to enrich in heavy elements the gas phase of the protosolar nebula, once they cross the amorphous-to-crystalline ice transition zone, following the original idea formulated by Monga & Desch. To do so, we use a simple accretion disk model coupled to modules depicting the radial evolution of icy particles and vapors, assuming growth, fragmentation, and crystallization of amorphous grains. We show that it is possible to accrete supersolar gas from the nebula onto proto-Jupiter’s core to form its envelope, and allowing it to match the observed volatile enrichments. Our calculations suggest that nebular gas, with a metallicity similar to that measured in Jupiter, can be accreted by its envelope if the planet is formed in the ~0.5–2 Myr time range and in the 0.5–20 au distance range from the Sun, depending on the adopted viscosity parameter of the disk. These values match a wide range of Jupiter’s formation scenarios, including in situ formation and migration/formation models.

Photoelectric conversion on Earth’s surface via widespread Fe- and Mn-mineral coatings

1,2,3Anhuai Lu et al. (>10)
Proceedings of the National Academy of Sciences of the United States of America 116, 9741-9746 Link to Article [https://doi.org/10.1073/pnas.1902473116]
1Beijing Key Laboratory of Mineral Environmental Function, School of Earth and Space Sciences, Peking University, 100871 Beijing, People’s Republic of China
2The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, 100871 Beijing, People’s Republic of China
3The Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, School of Geosciences and Info-Physics, Central South University, 410083 Changsha, People’s Republic of China

Sunlight drives photosynthesis and associated biological processes, and also influences inorganic processes that shape Earth’s climate and geochemistry. Bacterial solar-to-chemical energy conversion on this planet evolved to use an intricate intracellular process of phototrophy. However, a natural nonbiological counterpart to phototrophy has yet to be recognized. In this work, we reveal the inherent “phototrophic-like” behavior of vast expanses of natural rock/soil surfaces from deserts, red soils, and karst environments, all of which can drive photon-to-electron conversions. Using scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and X-ray absorption spectroscopy, Fe and Mn (oxyhydr)oxide-rich coatings were found in rock varnishes, as were Fe (oxyhydr)oxides on red soil surfaces and minute amounts of Mn oxides on karst rock surfaces. By directly fabricating a photoelectric detection device on the thin section of a rock varnish sample, we have recorded an in situ photocurrent micromapping of the coatings, which behave as highly sensitive and stable photoelectric systems. Additional measurements of red soil and powder separated from the outermost surface of karst rocks yielded photocurrents that are also sensitive to irradiation. The prominent solar-responsive capability of the phototrophic-like rocks/soils is ascribed to the semiconducting Fe- and Mn (oxyhydr)oxide-mineral coatings. The native semiconducting Fe/Mn-rich coatings may play a role similar, in part, to photosynthetic systems and thus provide a distinctive driving force for redox (bio)geochemistry on Earth’s surfaces.

Soil simulant preparation for lunar deep drilling exploration: Modeling and validation

1,2Junyue Tang,1 Shengyuan Jiang,1Qiquan Quan,1Jieneng Liang,1Yi Shen,1Ye Tian,3Fengpei Yuan
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2019.05.005]
1State Key Laboratory of Robotics and System, Harbin Institute of Technology, No.92, Xidazhi St., Nangang Dist, Harbin, 150001, PR China
2Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Rd., Evanston, IL, 60208, USA
3Department of Mechanical, Aerospace and Biomedical Engineering, The University of Tennessee, Knoxville, 124 Perkins Hall, Knoxville, TN, 37996, USA

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