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Feather features (FFs) in quartz consist of a planar fracture (PF) and associated fine lamellae (FF lamellae; FFL) and have been observed in various natural impact structures. However, the mechanisms and conditions of FF formation are poorly understood. We conducted shock recovery experiments on granite using decaying compressive pulses to investigate the formation conditions of FFs. We characterized the recovered samples using an optical microscope equipped with a universal stage, a scanning electron microscope combined with an electron back‐scattered diffraction detector, and a transmission electron microscope. We found that FFs are formed over a wide range of peak pressures (2–18 GPa) and that FFs can be divided into at least three types (I–III) based on the crystallographic orientation of the PFs and FFL, the angle between the orientation of the FFL and the propagation direction of the compression wave, and the presence/absence of amorphous silica in the FFL. The peak pressures that produce type I–III FFs are estimated to be <12, 12–14, and >16 GPa, respectively. We propose that FFs can be used as a shock barometer for quartz‐bearing rocks. Plain Language Summary: Our research focused on a unique deformation feature in quartz, known as feather features (FFs), which are found where hypervelocity impacts of celestial bodies have occurred. These features include a main crack and several fine, feather‐like lines emanating from the main crack. We conducted shockwave experiments on granite, a common quartz‐bearing rock by simulating the shock conditions of impacts onto Earth's surface. We used various microscopic techniques to observe the experimentally shocked quartz. We show that FFs form under a wide range of pressures from 20,000× to 180,000× atmospheric pressure. The FFs can be divided into three types relating to the peak pressure, based on the orientation of the feather‐like lines with respect to the crystal lattice and the direction of shockwave propagation, and whether vitrification occurred. At pressures below ∼120,000× atmospheric pressure, the main crack and fine lines have specific orientations (type I), but these orientations change when the pressure is >120,000× atmospheric pressures (type II). The feather‐like lines transform from simple cracks to structures filled with glass at a peak pressure of >140,000–160,000× atmospheric pressure (type III). The nature of the FFs means that the three types of FFs are a useful shock barometer for ancient impact events. Key Points: Impact experiments revealed that feather features in quartz are produced at peak pressures of 2–18 GPaThe feather features can be divided into at least three types that relate to the peak pressureFeather features can be used as a shock barometer for estimating peak pressures in geological studies [ABSTRACT FROM AUTHOR]

Knowledge of the shock behavior of planetary materials is essential to interpret shock metamorphism documented in rocks at hypervelocity impact structures on Earth, in meteorites, and in samples retrieved in space missions. Although our understanding of shock metamorphism has improved considerably within the last decades, the effects of friction and plastic deformation on shock metamorphism of complex, polycrystalline, non‐porous rocks are poorly constrained. Here, we report on shock‐recovery experiments in which natural granite was dynamically compressed to 0.5–18 GPa by singular, hemispherically decaying shock fronts. We then combine petrographic observations of shocked samples that retained their pre‐impact stratigraphy with distributions of peak pressures, temperatures, and volumetric strain rates obtained from numerical modeling to systematically investigate progressive shock metamorphism of granite. We find that the progressive shock metamorphism of granite observed here is mainly consistent with current classification schemes. However, we also find that intense shear deformation during shock compression and release causes the formation of highly localized melt veins at peak pressures as low as 6 GPa, which is an order of magnitude lower than currently thought. We also find that melt veins formed in quartz grains compressed to >10–12 GPa contain the high‐pressure silica polymorph stishovite. Our results illustrate the significance of shear and plastic deformation during hypervelocity impact and bear on our understanding of how melt veins containing high‐pressure polymorphs form in moderately shocked terrestrial impactites or meteorites. Plain Language Summary: When asteroids, comets, or smaller fragments thereof impact the solid surfaces of planets, moons, or other asteroids, the rocks they strike undergo sudden and irreversible changes while an impact crater forms. These material changes are called shock metamorphism and result from the extremely high pressures, temperatures, and deformation rates caused by the impact. However, the role of rapid shear deformation on impact heating and shock metamorphism is poorly understood. Using a novel experimental setup, we performed shock‐wave experiments with granite, a naturally occurring rock, that allows us to study the role of extreme deformation rates during impact‐crater formation. Furthermore, our experimental setup allows us to avoid several pitfalls such as excavation and ejection of shocked material from a growing impact crater or multiple reflections of shock waves at sample containers that typically plagued previous experiments. We find that intense shear deformation during crater formation results in significant but highly localized heating. This additional heating causes melting of granite at shock pressures as low as 6 GPa, which is about 10 times less than currently thought. Our findings may explain how thin melt veins often observed in shock‐metamorphosed meteorites or rocks sampled from terrestrial impact craters have formed. Key Points: We performed shock recovery experiments with granite and spherically decaying compressive waves; numerical models constrain peak pressuresShocked granite samples are found to retain pre‐impact stratigraphy and to document shock‐stage transitions between <0.5 and ∼18 GPaShear‐induced melting of granite at bulk peak pressures as low as 6 GPa; stishovite nucleated as a liquidus phase in melt veins at >10 GPa [ABSTRACT FROM AUTHOR]

Basaltic rocks occur widely on the terrestrial planets and differentiated asteroids, including the asteroid 4 Vesta. We conducted a shock recovery experiment with decaying compressive pulses on a terrestrial basalt at the Chiba Institute of Technology, Japan. The sample recorded a range of pressures, and shock physics modeling was conducted to add a pressure scale to the observed shock features. The shocked sample was examined by optical and electron microscopy, electron back‐scattered diffractometry, and Raman spectroscopy. We found that localized melting occurs at a lower pressure (∼10 GPa) than previously thought (>20 GPa). The shocked basalt near the epicenter represents "shock degree C" of a recently proposed classification scheme for basaltic eucrites and, as such, our results provide a pressure scale for the classification scheme. Finally, we estimated the total fraction of the basaltic eucrites classified as shock degree C to be ∼15% by assuming the impact velocity distribution onto Vesta. Plain Language Summary: Basaltic rocks occur on numerous planetary bodies, including Mars, the Moon, and the asteroid Vesta. Shock metamorphic features in meteorites from such bodies are the ancient imprints of past impact events. We can extract information about the bombardment histories experienced by such bodies if we have an accurate method to link the degree of metamorphism to the impact conditions. Although two such methods for basaltic rocks have been published, one of these does not have a scale that relates the shock features and peak pressures. In this study, we designed an impact experiment with a terrestrial basalt sample to add a pressure scale to one of these methods. We found that basaltic materials are more easily melted than previously expected. The shock features of our shocked sample match "shock degree C." The required pressure for producing the materials classified into this shock degree is 1–2 × 105 times greater than atmospheric pressure. Our results may provide insights into impact processes on Vesta. We estimate that the total fraction of meteorites from Vesta classified into shock degree C is ∼15%. Key Points: We investigated the shock effects in basaltic rocks with impact experiments and shock physics modelingWe added a pressure scale to the shock degree classification for basaltic eucrites, allowing us to link our results with the Stöffler tableLocalized melting occurs from 10 GPa rather than 20 GPa as previously thought [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.04.015 Byline: Sho Fukuzaki (a), Yasuhito Sekine (a), Hidenori Genda (b), Seiji Sugita (a), Toshihiko Kadono (c), Takafumi Matsui (d) Keywords: Titan; Atmospheres, Evolution; Impact processes; Satellites, Atmospheres Abstract: Chemical reactions and volatile supply through hypervelocity impacts may have played a key role for the origin and evolution of both planetary and satellite atmospheres. In this study, we evaluate the role of impact-induced N.sub.2 production from reduced nitrogen-bearing solids proposed to be contained in Titan's crust, ammonium sulfate ((NH.sub.4).sub.2SO.sub.4), for the replenishment of N.sub.2 to the atmosphere in Titan's history. To investigate the conversion of (NH.sub.4).sub.2SO.sub.4 into N.sub.2 by hypervelocity impacts, we measured gases released from (NH.sub.4).sub.2SO.sub.4 that was exposed to hypervelocity impacts created by a laser gun. The sensitivity and accuracy of the measurements were enhanced by using an isotope labeling technique for the target. We obtained the efficiency of N.sub.2 production from (NH.sub.4).sub.2SO.sub.4 as a function of peak shock pressure ranging from [approximately equal to]8 to [approximately equal to]45GPa. Our results indicate that the initial and complete shock pressures for N.sub.2 degassing from (NH.sub.4).sub.2SO.sub.4 are [approximately equal to]10 and [approximately equal to]25GPa, respectively. These results suggest that cometary impacts on Titan (i.e., impact velocity v.sub.i [approximately equal to]8km/s) produce N.sub.2 efficiently; whereas satellitesimal impacts during the accretion (i.e., v.sub.i Author Affiliation: (a) Department of Complexity Science and Engineering, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8561, Japan (b) Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo 113-0033, Japan (c) Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita 565-0871, Japan (d) Planetary Explorations Research Center, Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino 275-0016, Japan Article History: Received 23 November 2009; Revised 21 April 2010; Accepted 21 April 2010

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.04.019 Byline: Satoru Yamamoto (a), Olivier S. Barnouin-Jha (b), Takashi Toriumi (c), Seiji Sugita (d), Takafumi Matsui (e) Keywords: Impact processes; Cratering; Collisional physics Abstract: The present paper describes observations of crater growth up to the time of transient crater formation and presents a new empirical model for transient crater growth as a function of time. Polycarbonate projectiles were impacted vertically into soda-lime glass sphere targets using a single-stage light-gas gun. Using a new technique with a laser sheet illuminating the target [Barnouin-Jha, O.S., Yamamoto, S., Toriumi, T., Sugita, S., Matsui, T., 2007. Non-intrusive measurements of the crater growth. Icarus, 188, 506-521], we measured the temporal change in diameter of crater cavities (diameter growth). The rate of increase in diameter at early times follows a power law relation, but the data at later times (before the end of transient crater formation) deviates from the power law relation. In addition, the power law exponent at early times and the degree of deviation from a power law at later times depend on the target. In order to interpret these features, we proposed to modify Maxwell's Z-model under the assumption that the strength of the excavation flow field decreases exponentially with time. We also derived a diameter growth model as: d(t)a[1-exp(-[beta]t)].sup.[gamma], where d(t) is the apparent diameter of the crater cavity at time t after impact, and [beta] and [gamma] are constants. We demonstrated that the diameter growth model could represent well the experimental data for various targets with different target material properties, such as porosity or angle of repose. We also investigated the diameter growth for a dry sand target, which has been used to formulate previous scaling relations. The obtained results showed that the dry sand target has larger degree of deviation from a power law, indicating that the target material properties of the dry sand target have a significant effect on diameter growth, especially at later times. This may suggest that the previously reported scaling relations should be reexamined in order to account for the late-stage behavior with the effect of target material properties. Author Affiliation: (a) Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba 305-8506, Japan (b) The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723, USA (c) Institute of Physical Education, Keio University, Yokohama, 223-8521, Japan (d) Graduate School of Frontier Sciences, University of Tokyo, Chiba, 277-8561, Japan (e) Planetary Exploration Research Center, Chiba Institute of Technology, Chiba, 275-0016, Japan Article History: Received 6 October 2008; Revised 2 April 2009; Accepted 6 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.01.009 Byline: Olivier S. Barnouin-Jha (a)(b), Satoru Yamamoto (b), Takashi Toriumi (b), Seiji Sugita (b), Takafumi Matsui (b) Keywords: Impact processes; Cratering Abstract: An experimental technique to measure crater growth is presented whereby a high speed video captures profiles of a crater forming after impact obtained using a vertical laser sheet centered on the impact point. Unlike previous so called 'quarter-space experiments,' where projectiles were launched along a transparent Plexiglas sheet so that growth of half a crater could be viewed, the use of the laser sheet permits viewing changes in crater shape without any physical interference to the cratering process. This technique indicates that for low velocity impacts (45[degrees]) are also seen, and could be due to the low friction angle of the target. Significant crater modification, which is rarely seen in 'quarter-space experiments,' is also observed and appears to be controlled by the dynamic angle of repose of the target. These latter observations indicate that differences in target friction angles may need to be considered when determining near rim ejecta-mass distributions and large-scale crater modification processes on the planets. Author Affiliation: (a) The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099, USA (b) Department of Complexity Sciences and Engineering, University of Tokyo, Kashiwa, Chiba 277-8561, Japan Article History: Received 17 January 2006; Revised 24 October 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.02.002 Byline: Satoru Yamamoto (a), Koji Wada (b), Norihisa Okabe (a), Takafumi Matsui (a) Keywords: Cratering; Impact processes; Collisional physics Abstract: We experimentally studied the formation and collapse processes of transient craters. Polycarbonate projectiles with mass of 0.49 g were impacted into the soda-lime glass sphere target (mean diameters of glass spheres are [approximately equal to]36, 72, and 220 [mu]m, respectively) using a single-stage light-gas gun. Impact velocity ranged from 11 to 329 mas.sup.-1. We found that the transient crater collapses even at laboratory scales. The shape (diameter and depth) of the transient crater differs from that of the final crater. The depth-rim diameter ratios of the final and transient craters are 0.11-0.14 and 0.26-0.27, respectively. The rim diameter of both the transient and final crater depends on target material properties; however, the ratio of final to transient crater diameter does not. This suggests that target material properties affect the formation process of transient craters even in the gravity regime, and must be taken into account when scaling experimental results to planetary scales. By observing impacts into glass sphere targets, we show that although the early stage of the excavation flow does not depend on the target material properties, the radial expansion of the cavity after the end of vertical expansion does. This suggests that the effect of target material properties is specifically important in the later part of the crater excavation and collapse. Author Affiliation: (a) Graduate School of Frontier Sciences, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8562, Japan (b) Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan Article History: Received 1 June 2005; Revised 31 January 2006

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.10.002 Byline: Koji Wada (a)(b), Hiroki Senshu (c), Takafumi Matsui (a) Keywords: Cratering; Impact processes; Computer techniques Abstract: A new numerical code based on the Distinct Element Method (DEM) is developed to study the impact cratering processes on granular material. This code has a potential advantage to simulate the cratering process on granular material, since the movement of discrete particles can be treated. To show the physical plausibility of this code, we conduct 3-D numerical simulations of vertical impact into granular material targets that consist of 384,000 particles, and compare the results with those from experimental studies. It is shown that the excavation stage of cratering derived from experimental studies is represented well by our simulation: the size of the crater cavity, and the ejecta velocity and angle distributions are consistent with those obtained in laboratory experiments. The impact simulation code developed in this study is thus suggested to be useful for the analysis of the impact cratering process on granular material. Author Affiliation: (a) Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa-shi, Chiba 277-8561, Japan (b) Institute of Low Temperature Science, Hokkaido University, N19-W8, Kita-ku, Sapporo 060-0819, Japan (c) Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima-cho, Yokosuka 237-0061, Japan Article History: Received 28 February 2005; Revised 6 September 2005

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.04.007 Byline: Satoru Yamamoto (a), Toshihiko Kadono (b), Seiji Sugita (a), Takafumi Matsui (a) Keywords: Impact processes; Cratering; Collisional physics; Regoliths Abstract: We measured the velocity distributions of impact ejecta with velocities higher than [approximately equal to]100 mas.sup.-1 (high-velocity ejecta) for impacts at variable impact angle [alpha] into unconsolidated targets of small soda-lime glass spheres. Polycarbonate projectiles with mass of 0.49 g were accelerated to [approximately equal to]250 mas.sup.-1 by a single-stage light-gas gun. The impact ejecta are detected by thin aluminum foils placed around the targets. We analyzed the holes on the aluminum foils to derive the total number and volume of ejecta that penetrated the aluminum foils. Using the minimum velocity of the ejecta for penetration, determined experimentally, the velocity distributions of the high-velocity ejecta were obtained at [alpha]=15[degrees], 30[degrees], 45[degrees], 60[degrees], and 90[degrees]. The velocity distribution of the high-velocity ejecta is shown to depend on impact angle. The quantity of the high-velocity ejecta for vertical impact ([alpha]=90[degrees]) is considerably lower than derived from a power-law relation for the velocity distribution on the low-velocity ejecta (less than 10 mas.sup.-1). On the other hand, in oblique impacts, the quantity of the high-velocity ejecta increases with decreasing impact angle, and becomes comparable to those derived from the power-law relation. We attempt to scale the high-velocity ejecta for oblique impacts to a new scaling law, in which the velocity distribution is scaled by the cube of projectile radius (scaled volume) and a horizontal component of impactor velocity (scaled ejection velocity), respectively. The high-velocity ejecta data shows a good correlation between the scaled volume and the scaled ejection velocity. Author Affiliation: (a) Mailbox 408, Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, University of Tokyo, Kashiwanoha, Kashiwa, Chiba 277-8562, Japan (b) IFREE, JAMSTEC, Kanagawa 273-0061, Japan Article History: Received 7 August 2004; Revised 22 February 2005

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.03.016 Byline: Yasuhito Sekine (a), Seiji Sugita (b), Takafumi Shido (c), Takashi Yamamoto (c), Yasuhiro Iwasawa (c), Toshihiko Kadono (d), Takafumi Matsui (b) Keywords: Fischer-Tropsch catalysis; Titan; Cassini-Huygens mission; Circum-planetary subnebula; Methane Abstract: Fischer-Tropsch catalysis, which converts CO and H.sub.2 into CH.sub.4 on the surface of iron catalyst, has been proposed to produce the CH.sub.4 on Titan during its formation process in a circum-planetary subnebula. However, Fischer-Tropsch reaction rate under the conditions of subnebula have not been measured quantitatively yet. In this study, we conduct laboratory experiments to determine CH.sub.4 formation rate and also conduct theoretical calculation of clathrate formation to clarify the significance of Fischer-Tropsch catalysis in a subnebula. Our experimental result indicates that the range of conditions where Fischer-Tropsch catalysis proceeds efficiently is narrow (T[approximately equal to]500-600K) in a subnebula because the catalysts are poisoned at temperatures above 600 K under the condition of subnebula (i.e., H.sub.2/CO=1000). This suggests that an entire subnebula may not become rich in CH.sub.4 but rather that only limited region of a subnebula may enriched in CH.sub.4 (i.e., CH.sub.4-rich band formation). Our experimental result also suggests that both CO and CO.sub.2 are converted into CH.sub.4 within time significantly shorter than the lifetime of the solar nebula at the optimal temperatures around 550 K. The calculation result of clathration shows that CO.sub.2-rich satellitesimals are formed in the catalytically inactive outer region of subnebula. In the catalytically active inner region, CH.sub.4-rich satellitesimals are formed. The resulting CH.sub.4-rich satellitesimals formed in this region play an important role in the origin of CH.sub.4 on Titan. When our experimental data are applied to a high-pressure model for subnebula evolution, it would predict that there should be CO.sub.2 underneath the Iapetus subsurface and no thick CO.sub.2 ice layer on Titan's icy crust. Such surface and subsurface composition, which may be observed by Cassini-Huygens mission, would provide crucial information on the origin of icy satellites. Author Affiliation: (a) Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan (b) Department of Complexity Science and Engineering, Graduate School of Frontier Science, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 227-8562, Japan (c) Department of Chemistry, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan (d) Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan Article History: Received 12 August 2004; Revised 4 March 2005

Titan, the largest satellite of Saturn, has a thick nitrogen/methane atmosphere with a thick global organic haze. A laboratory analogue of Titan's haze, called tholin, was formed in an inductively coupled plasma from nitrogen/methane = 90/10 gas mixture at various pressures ranging from 13 to 2300 Pa. Chemical and optical properties of the resulting tholin depend on the deposition pressure in cold plasma. Structural analyses by IR and UV/VIS spectroscopy, microprobe laser desorption/ionization mass spectrometry, and Raman spectroscopy suggest that larger amounts of aromatic ring structures with larger cluster size are formed at lower pressures (13 and 26 Pa) than at higher pressures (160 and 2300 Pa). Nitrogen is more likely to incorporate into carbon networks in tholins formed at lower pressures, while nitrogen is bonded as terminal groups at higher pressures. Elemental analysis reveals that the carbon/nitrogen ratio in tholins increases from 1.5-2 at lower pressures to 3 at 2300 Pa. The increase in the aromatic compounds and the decrease in C/N ratio in tholin formed at low pressures indicate the presence of the nitrogen-containing polycyclic aromatic compounds in tholin formed at low pressures. Tholin formed at high pressure (2300 Pa) consists of a polymer-like branched chain structure terminated with -C[H.sub.3], -N[H.sub.2], and -C[equivalent to]N with few aromatic compounds. Reddish-brown tholin films formed at low pressures (13-26 Pa) shows stronger absorptions (almost 10 times larger k-value) in the UV/VIS range than the yellowish tholin films formed at high pressures (160 and 2300 Pa). The tholins formed at low pressures may be better representations of Titan's haze than those formed at high pressures, because the optical properties of tholin formed at low pressures agree well with that of Khare et al. (1984a, Icarus 60, 127-137), which have been shown to account for Titan's observed geometric albedo. Thus, the nitrogen-containing polycyclic aromatic compounds we find in tholin formed at low pressure may be present in Titan's haze. These aromatic compounds may have a significant influence on the thermal structure and complex organic chemistry in Titan's atmosphere, because they are efficient absorbers of UV radiation and efficient charge exchange intermediaries. Our results also indicate that the haze layers at various altitudes might have different chemical and optical properties. Keywords: Titan; Haze; Tholin; Spectroscopy; Organic chemistry; Nitrogen-containing polycyclic aromatic compounds

Shock metamorphism of minerals in meteorites provides insights into the ancient Solar System. Calcite is an abundant aqueous alteration mineral in carbonaceous chondrites. Return samples from the asteroids Ryugu and Bennu are expected to contain calcite‐group minerals. Although shock metamorphism in silicates has been well studied, such data for aqueous alteration minerals are limited. Here, we investigated the shock effects in calcite with marble using impact experiments at the Planetary Exploration Research Center of Chiba Institute of Technology. We produced decaying compressive pulses with a smaller projectile than the target. A metal container facilitates recovery of a sample that retains its pre‐impact stratigraphy. We estimated the peak pressure distributions in the samples with the iSALE shock physics code. The capability of this method to produce shocked grains that have experienced different degrees of metamorphism from a single experiment is an advantage over conventional uniaxial shock recovery experiments. The shocked samples were investigated by polarizing microscopy and X‐ray diffraction analysis. We found that more than half of calcite grains exhibit undulatory extinction when peak pressure exceeds 3 GPa. This shock pressure is one order of magnitude higher than the Hugoniot elastic limit (HEL) of marble, but it is close to the HEL of a calcite crystal, suggesting that the undulatory extinction records dislocation‐induced plastic deformation in the crystal. Finally, we propose a strategy to re‐construct the maximum depth of calcite grains in a meteorite parent body, if shocked calcite grains are identified in chondrites and/or return samples from Ryugu and Bennu. Plain Language Summary: Carbonaceous chondrites are a group of meteorites found on Earth, which contain significant amounts of water and organic materials. Ancient impacts onto their parent bodies caused irreversible changes to the minerals in these meteorites, which is termed shock metamorphism. If the relationship between the metamorphism and intensity of the impact can be understood, it would be possible to elucidate the histories of meteorite parent bodies. We investigated shock metamorphism of calcite, which is an abundant aqueous alteration mineral in carbonaceous chondrites, and may also be present in return samples from the asteroids Ryugu and Bennu. Our experiments involved rapid compression during laboratory impacts onto marble blocks. We found that shocked calcite exhibits a specific feature called undulatory extinction under microscope and quantified the strength of the compressive pulse required to produce this feature, which is 30,000 times greater than the atmospheric pressure. Given that such conditions cannot be easily reached on meteorite parent bodies and/or on Ryugu and Bennu, except during hypervelocity impacts, calcite grains showing this feature provide evidence for past impact events. Key Points: We present a method to efficiently investigate the shock effects in minerals in rock samples with sizes of >20 mmImpact experiments with decaying compressive pulses revealed the shock effects in marble, which is a macro block of calcite (CaCO3)Calcite that experiences compression of >3 GPa exhibits undulatory extinction [ABSTRACT FROM AUTHOR]

Radiation phenomena are usually observed during fracture of quartz-bearing rocks. Since quartz is a piezoelectric material, the associated electrical processes such as the electrification of fracture surface and the flight of electrons between fracture surfaces should be important for radiation during fractures. In this article, supposing that travelling electrons between crack surfaces cause the radiation, we experimentally investigate X-ray emission in a vacuum and visible-light emission in the atmosphere during rock and mineral fracture and verify the consistency of both emissions. The number of electrons in flight between surfaces during fracture that result in X-ray is estimated and the comparison with the number of photons in visible light suggests that one electron repeatedly collides with N2 molecules. The estimated number of collisions resulting in a visible-light emission is slightly less than the expected upper limit. This is reasonable because the collision would cause the light emission not always in the wavelengths of visible light. Moreover, the number of electrons resulting in X-rays is comparable with the number of electrons resulting in the emission of radio waves during fracture obtained in previous studies. Thus, we conclude that the radiations during fracture can be attributed to the flight of electrons between fracture surfaces. Finally, we evaluate the feasibility of observing the X-ray emission in planetary exploration and the radio waves and the visible light in natural earthquakes and find that these radiations are observable. [ABSTRACT FROM AUTHOR]

The Iron Age was the time when people acquired iron processing technology and is generally thought to have begun after 1200 B.C. Some prehistoric iron artifacts made of iron meteorites are dated from the Bronze Age. A nicely preserved meteoritic iron dagger was found in the tomb of King Tutankhamen (1361–1352 B.C.) of ancient Egypt. Yet, its manufacturing method and origin remain unclear. Here, we report nondestructive two‐dimensional chemical analyses of the Tutankhamen iron dagger, conducted at the Egyptian Museum of Cairo. Elemental mapping of Ni on the dagger blade surface shows discontinuous banded arrangements in places with "cubic" symmetry and a bandwidth of about 1 mm, suggesting a Widmanstätten pattern. The intermediate Ni content (11.8 ± 0.5 wt%) with the presence of the Widmanstätten pattern implies the source meteorite of the dagger blade to be octahedrite. The randomly distributed sulfur‐rich black spots are likely remnants of troilite (FeS) inclusions in iron meteorite. The preserved Widmanstätten pattern and remnant troilite inclusion show that the iron dagger was manufactured by low‐temperature (<950 °C) forging. The gold hilt with a few percent of calcium lacking sulfur suggests the use of lime plaster instead of gypsum plaster as an adhesive material for decorations on the hilt. Since the use of lime plaster in Egypt started during the Ptolemaic period (305–30 B.C.), the Ca‐bearing gold hilt hints at its foreign origin, possibly from Mitanni, Anatolia, as suggested by one of the Amarna letters saying that an iron dagger with gold hilt was gifted from the king of Mitanni to Amenhotep III, the grandfather of Tutankhamen. [ABSTRACT FROM AUTHOR]

Asteroid (99942) Apophis is a potentially hazardous asteroid. The Korea Astronomy and Space Science Institute (KASI) recently proposed a rendezvous mission with Apophis, with a planned asteroid observation campaign to help determine the mission strategy in advance. In this study, we performed multicolor photometric observations of Apophis using the 1.0 m telescope at Kawabe Cosmic Park on 2021 March 10. The visible colors (g ′, r ′, and i ′) of Apophis were obtained. The average colors of Apophis during our observations were as follows: g ′ − r ′ = 0.618 ± 0.021 and r ′ − i ′ = 0.180 ± 0.021. No significant color variation was observed in r ′ − i ′, but a slight variation may have occurred in g ′ − r ′ during the observation period of 4.63 hr. The obtained colors appeared to match those of an Sq-class asteroid, which is the asteroid type previously determined for Apophis by Binzel et al. (2009 , Icarus, 200, 480) using the visible to near-infrared (0.55–2.45 μm) reflectance spectrum. [ABSTRACT FROM AUTHOR]

High‐speed impact ejecta at velocities comparable to the impact velocity are expected to contribute to material transport between planetary bodies and deposition of ejecta far from the impact crater. We investigated the behavior of high‐speed ejecta produced at angles of 45° and 90°, using both experimental and numerical methods. The experimental system developed at the Planetary Exploration Research Center of Chiba Institute of Technology (Japan) allowed us to observe the initial growth of the ejecta. We succeeded in imaging high‐speed ejecta at 0.2 μs intervals for impacts of polycarbonate projectiles of 4.8 mm diameter onto a polycarbonate plate at an impact velocity of ~4 km s−1. Smoothed particle hydrodynamics (SPH) simulations of various numerical resolutions were conducted for the same impact conditions as pertaining to the experiments. We compared the morphology and velocities of the ejecta for the experiments and simulations, and we confirmed a close match for high‐resolution simulations (with ≥106 SPH particles representing the projectile). According to the ejecta velocity distributions obtained from our high‐resolution simulations, the ejection velocities of the high‐speed ejecta for oblique impacts are much greater than those for vertical impacts. The translational motion of penetrating projectiles parallel to the target surface in oblique impacts could cause long‐term, sustained acceleration at the root of the ejecta. Plain Language Summary: Impact ejection is an inevitable outcome following hypervelocity impacts. Ejecta produced by the "spallation" process, which generates lightly shocked, high‐speed materials, are thought to be important in the context of (Litho)Panspermia, crater chronology, and the origin of Martian meteorites and tektites. The nature of impact spallation is not fully understood, especially in oblique impacts. In this study, we investigate the effects of the impact obliquity on spallation using both experimental and numerical approaches. The ejection behavior observed in the laboratory is well reproduced by our numerical code when we employ a sufficiently high spatial resolution. The experimentally validated numerical model allows us to address the nature of the impact‐driven flow field. We found that the acceleration efficiency during oblique impacts is much better than during vertical impacts. Key Points: We performed 200 ns imaging of high‐speed ejecta during oblique impactsComputations under the same conditions as pertaining to the experiments reproduced the observed ejection behavior very wellVelocity boost owing to sustained compression works effectively for oblique impacts [ABSTRACT FROM AUTHOR]