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Submarine mud volcanoes (MVs) have attracted significant interest in the scientific community for obtaining clues on the subsurface biosphere. On-land MVs, which are much less focused in this context, are equally important, and they may even provide insights also for astrobiology of extraterrestrial mud volcanism. Hereby, we characterized microbial communities of two active methane-seeping on-land MVs, Murono and Kamou, in central Japan. 16S rRNA gene profiling of those sites recovered the dominant archaeal sequences affiliated with methanogens. Anaerobic methanotrophs (ANME), with the subgroups ANME-1b and ANME-3, were recovered only from the Murono site albeit a greatly reduced relative abundance in the community compared to those of typical submarine MVs. The bacterial sequences affiliated to Caldatribacteriota JS1 were recovered from both sites; on the other hand, sulfate-reducing bacteria (SRB) of Desulfobulbaceae was recovered only from the Murono site. The major difference of on-land MVs from submarine MVs is that the high concentrations of sulfate are not always introduced to the subsurface from above. In addition, the XRD analysis of Murono shows the absence of sulfate-, sulfur-related mineral. Therefore, we hypothesize one scenario of ANME-1b and ANME-3 thriving at the depth of the Murono site independently from SRB, which is similar to the situations reported in some other methane-seeping sites with a sulfate-depleted condition. We note that previous investigations speculate that the erupted materials from Murono and Kamou originate from the Miocene marine strata. The fact that SRB (Desulfobulbaceae) capable of associating with ANME-3 was recovered from the Murono site presents an alternative scenario: the old sea-related juvenile water somehow worked as the source of additional sulfur-related components for the SRB-ANME syntrophic consortium forming at a deeper zone of the site. However, the reason for the differences between Murono and Kamou is still unknown, and this requires further investigation.

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.

Dry lakebeds might constitute large volatile reservoirs on Mars. Hypervelocity impacts onto ancient dry lakebeds would have affected the volatile distribution on Mars. We developed a new experimental method to investigate the response of evaporitic minerals (halite and gypsum) to impact shocks in an open system. This technique does not result in chemical contamination from the operation of the gas gun. The technique is termed the “two‐valve method,” and the gun system is located in the Planetary Exploration Research Center, Chiba Institute of Technology, Japan. We detected the vaporization of halite at 31 GPa and devolatilization from gypsum at 11 GPa, suggesting that impact‐induced volatile release from dry lakebeds has periodically occurred throughout Martian history. The vaporization of halite deposits might have enhanced the production of perchlorates, which are found globally on Mars. The water loss from gypsum possibly explains the coexisting types of Ca‐sulfates found in Gale Crater. We used a new experimental technique to investigate the result of a meteoroid impact into an evaporitic deposit on Mars. Although two‐stage light gas guns are ideal projectile launchers, the dirty gas from the gun has been a long‐standing limitation of this technique that so far greatly complicated analysis of the vapors that are generated due to such impacts. Our new method overcomes this limitation and allows us to measure impact‐generated vapor from evaporitic minerals. We detected NaCl vapor from halite and water vapor from gypsum at velocities lower than the typical impact velocities onto Mars. This suggests that volatile release from ancient dry lakebeds has periodically occurred throughout Martian history, due to stochastic meteoroid impacts. The nature of perchlorates and Ca‐sulfates found on Mars can be interpreted as the result of hypervelocity impacts onto dry lakebeds rich in evaporitic minerals. Gas release from halite and gypsum was studied using a two‐stage light gas gun setup that avoids contamination of impact vapors from gun‐related gasesVaporization of halite at 31 GPa and devolatilization (water loss) from gypsum at 11 GPa were detectedImpacts might have resulted in efficient production of perchlorates in Martian soil and produced the anhydrite found in Gale Crater

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. 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. 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 We performed shock recovery experiments with granite and spherically decaying compressive waves; numerical models constrain peak pressures Shocked granite samples are found to retain pre‐impact stratigraphy and to document shock‐stage transitions between <0.5 and ∼18 GPa Shear‐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

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. 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 × 105times 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%. 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 We investigated the shock effects in basaltic rocks with impact experiments and shock physics modeling We added a pressure scale to the shock degree classification for basaltic eucrites, allowing us to link our results with the Stöffler table Localized melting occurs from 10 GPa rather than 20 GPa as previously thought

The mass extinction event at the Cretaceous/Palaeogene boundary 65.5 Myr ago has been widely attributed to the Chicxulub impact, but the mechanisms of extinction remain debated. In the oceans, near-surface planktonic foraminifera suffered severe declines, in contrast to the relatively high survival rates of bottom-dwelling benthic foraminifera. The vapour produced by an impact into Chicxulub’s target rocks, which include sulphate-rich anhydrite, could have led to global acid rain, which can explain the pattern of oceanic extinctions. However, it has been suggested that most of the sulphur in the target rocks would have been released as sulphur dioxide and would have stayed in the stratosphere for a long time. Here we show, from impact experiments into anhydrite at velocities exceeding 10 km s-1, that sulphur trioxide dominates over sulphur dioxide in the resulting vapour cloud. Our experiments suggest that the Chicxulub impact released a huge quantity of sulphur trioxide into the atmosphere, where it would have rapidly combined with water vapour to form sulphuric acid aerosol particles. We also find, using a theoretical model of aerosol coagulation following the Chicxulub impact, that larger silicate particles ejected during the impact efficiently scavenge sulphuric acid aerosol particles and deliver the sulphuric acid to the surface within a few days. The rapid surface deposition of sulphuric acid would cause severe ocean acidification and account for preferential extinction of planktonic over benthic foraminifera.

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. 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. 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 We present a method to efficiently investigate the shock effects in minerals in rock samples with sizes of >20 mm Impact 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—We measured 852 sets of planar deformation features (PDFs) in shocked quartz grains in impactite samples of the Yaxcopoil (YAX‐1) core and from 4 Cretaceous/Tertiary (K/T) boundary deposits: the Monaca, the Cacarajícara, and the Peñalver formations in Cuba, and DSDP site 536, within 800 km of the Chicxulub crater, in order to investigate variations of PDF orientations in the proximity of the crater. Orientations of PDFs show a broad distribution with peaks at ω {101¯3}, π {101¯2}, and ω {111¯2}, plus r, z {1011¯} orientations with minor c(0001), s{112¯1}, t{224¯1} plus x{516¯1}, and m{101¯0} plus a{112¯0} orientations. Planar deformation features with c(0001) orientation are relatively more abundant in the proximity of the Chicxulub crater than in distal sites such as North America, the Pacific Ocean, and Europe. This feature indicates that in the proximity of the crater, part of the shocked quartz grains in the K/T boundary deposits were derived from the low shock pressure zones. Moreover, the orientations of PDFs with ω {112¯2} plus r, z {101¯1} are high in our studied sites, and frequencies of these orientations decrease with increasing distance from the crater. On the other hand, absence of c(0001) and the rare occurrence of PDFs with ?ω {112¯2} plus r, z {101¯1} orientations in the sample from the YAX‐1 core that was taken at the top of the impactite layer of the Chicxulub crater suggests that the sampling horizon that reflects a certain cratering stage is also an important factor for variations in shocked quartz.

The thermal dissociation of SiO2in impact-induced vapor is very important because it controls the redox state of the vapor. However, the thermal dissociation of SiO2and its recombination are not well understood. The present study investigates experimentally the kinetics of the Si-O recombination process at high temperatures. Laser-induced quartz vapor is observed by means of time-resolved spectroscopy, and the atomic lines of Si and molecular bands of SiO are measured in order to estimate the temperature and the column densities of Si and SiO. The results of these experiments show that Si and O recombine as the vapor cools from 5000 to 3000 K. A comparison of the observed chemical composition and equilibrium calculations suggests that the recombination reaction between Si and O proceeds rather efficiently under a condition that differs significantly from the thermo-chemical equilibrium. This result is explained well if the rate constant of the Si-O recombination process does not depend strongly on the temperature; the activation energy is very small. These results suggest that the Si-O recombination process may not be approximated by a frequently-used ‘freeze-out’ model.

Abstract—Fischer‐Tropsch catalysis, by which CO and H2are converted to CH4on the surface of transition metals, has been considered to be one of the most important chemical reactions in many planetary processes, such as the formation of the solar and circumplanetary nebulae, the expansion of vapor clouds induced by cometary impacts, and the atmospheric re‐entry of vapor condensate due to asteroidal impacts. However, few quantitative experimental studies have been conducted for the catalytic reaction under conditions relevant to these planetary processes. In this study, we conduct Fischer‐Tropsch catalytic experiments at low pressures (1.3 times 10−4bar ≤ P≤ 5.3 times 10−1bar) over a wide range of H2/CO ratios (0.25–1000) using pure iron, pure nickel, and iron‐nickel alloys. We analyze what gas species are produced and measure the CH4formation rate. Our results indicate that the CH4formation rate for iron catalysts strongly depends on both pressure and the H2/CO ratio, and that nickel is a more efficient catalyst at lower pressures and lower H2/CO ratios. This difference in catalytic properties between iron and nickel may come from the reaction steps concerning disproportionation of CO, hydrogenation of surface carbon, and the poisoning of the catalyst. These results suggest that nickel is important in the atmospheric re‐entry of impact condensate, while iron is efficient in circumplanetary subnebulae. Our results also indicate that previous numerical models of iron catalysis based on experimental data at 1 bar considerably overestimate CH4formation efficiency at lower pressures, such as the solar nebula and the atmospheric re‐entry of impact condensate.

Abstract—The possibility of ocean water invasion into the Chicxulub crater following the impact at the Cretaceous/Tertiary boundary was investigated based on examination of an impactite between approximately 794.63 and 894.94 m in the Yaxcopoil‐1 (Yax‐1) core. The presence of cross lamination in the uppermost part of the impactite suggests the influence of an ocean current at least during the sedimentation of this interval. Abundant occurrence of nannofossils of late Campanian to early Maastrichtian age in the matrices of samples from the upper part of the impactite suggests that the carbonate sediments deposited on the inner rim margin and outside the crater were eroded and transported into the crater most likely by ocean water that invaded the crater after its formation. The maximum grain size of limestone lithics and vesicular melt fragments, and grain and bulk chemical compositions show a cyclic variation in the upper part of the impactite. The upward fining grain size and the absence of erosional contact at the base of each cycle suggest that the sediments were derived from resuspension of units elsewhere in the crater, most likely by high energy currents association with ocean water invasion.

AbstractThe possibility of ocean water invasion into the Chicxulub crater following the impact at the Cretaceous/Tertiary boundary was investigated based on examination of an impactite between approximately 794.63 and 894.94 m in the Yaxcopoil‐1 (Yax‐1) core. The presence of cross lamination in the uppermost part of the impactite suggests the influence of an ocean current at least during the sedimentation of this interval. Abundant occurrence of nannofossils of late Campanian to early Maastrichtian age in the matrices of samples from the upper part of the impactite suggests that the carbonate sediments deposited on the inner rim margin and outside the crater were eroded and transported into the crater most likely by ocean water that invaded the crater after its formation. The maximum grain size of limestone lithics and vesicular melt fragments, and grain and bulk chemical compositions show a cyclic variation in the upper part of the impactite. The upward fining grain size and the absence of erosional contact at the base of each cycle suggest that the sediments were derived from resuspension of units elsewhere in the crater, most likely by high energy currents association with ocean water invasion.

We show that the surface of a planet growing by planetesimal impact is heated over the melting temperature of the surface materials due to the blanketing effect of an impact induced H2O atmosphere with the present H2O abundance of the Earth even when the accretion time is as long as 108years. Hence, a ‘magma ocean’ covering the entire surface was formed on the Earth and Moon and other terrestrial planets during their formations.

On the basis of the model proposed by Matsui and Abe, we will show that two major factors — distance from the Sun and the efficiency of retention of accretional energy — control the early evolution of the terrestrial planets. A diagram of accretional energy versus the optical depth of a proto-atmosphere provides a means to follow the evolutionary track of surface temperature of the terrestrial planets and an explanation for why the third planet in our solar system is an ‘aqua’-planet.

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 ≥106SPH 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. 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. 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

Early rapid formation of the atmosphere and hydrosphere on the terrestrial planets has recently been proposed1,2. Here we present a quantitative study of this process during accretion by planetesimal impacts. These impacts increase the surface temperature and thus affect the formation of either a proto-atmosphere or a proto-hydrosphere by degassing of volatiles. We show that an impact-induced H2O atmosphere increases the surface temperature of the Earth to a stage where a magma ocean is possible, with the total amount of H2O in the proto-atmosphere clustering around 1021kg, this number is rather insensitive to variations in the input data. We suggest that the apparent coincidence of the H2O abundance in the proto-atmosphere with the present mass (˜1.4 × 1021kg) of the ocean is evidence for an impact origin for the atmosphere and hydrosphere.

High-velocity impacts of planetesimals onto a growing planet result in the impact-degassing of volatiles and the formation of an impact-induced atmosphere. Because of the blanketing effect of such an atmosphere, it is likely that the surface of the proto-Venus melted once the radius exceeded ∼40% of the final radius. The final mass of H2O in the impact-generated atmosphere, predicted to be ∼1021kg on the basis of thermal evolution models of the growing proto-Venus, does not depend on the initial water content of the Venus-forming planetesimals and is almost identical to the present mass of the Earth's oceans. We show here that an impact-induced H2O atmosphere of ∼1021kg mass probably formed on both Venus and Earth during accretion, but that whereas H2O in the proto-atmosphere of the Earth could condense to form a hot (∼600 K) ocean, such condensation probably did not occur on Venus.

ALL planets and satellites are generally believed to have formed by accretion of small bodies. The craters on the Moon, Mercury and Mars give clear evidence that the accretion of small bodies was of major importance, at least during the last phase of their formation. It is very likely that collision and fragmentation of planetesimals played a key part in the accretionary stage of planets. As suggested by Hartung1, accumulation and fragmentation of planetesimals may have competed in the planetary accretion process, and a planetesimal which could survive catastrophic destruction may have become a planet. On the basis of the accretion model of planet formation, we propose a new idea in which we explain why minor planets are ‘minor’ and could not grow to a full-size planet. These results also substantiate Orowan's2idea that terrestrial planets accreted inhomogeneously, with iron being the first to accumulate and silicates the second.