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Japan Aerospace Exploration Agency's Martian Moons eXploration (MMX) mission will launch a spacecraft in 2024 to return samples from Phobos in 2029. Curatorial work for the returned Phobos samples is critical for the sample allocation without degrading the sample integrity and subsequent sample analysis that will provide new constraints on the origin of Phobos and the evolution of the circum‐Mars environment. The Sample Analysis Working Team of the MMX is designing the sample curation protocol. The curation protocol consists of three phases: (1) quick analysis (extraction and mass spectrometry for gases), (2) pre‐basic characterization (bulk‐scale observation), and (3) basic characterization (grain‐by‐grain observation and allocation of the sample aliquots). Nondestructive analyses within the clean chamber (e.g., visible and near‐infrared spectral imaging) and outside the chamber (e.g., gas mass spectrometry) are incorporated into the curation flow in coordination with the MMX mission instrument teams for ground‐truthing the remote‐sensing data sets. The MMX curation/sample analysis flow enables the seamless integration between the sample and remote‐sensing data sets to maximize the scientific value of the collected Phobos samples. [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]

Understanding the origins of the diversity in terrestrial planets is a fundamental goal in Earth and planetary sciences. In the Solar System, Venus has a similar size and bulk composition [...]

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

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]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.09.007 Byline: Hidenori Genda (a), Masahiro Ikoma (b) Keywords: Atmospheres; evolution; Earth; Solar nebula Abstract: The origin of the Earth's ocean has been discussed on the basis of deuterium/hydrogen ratios (D/H) of several sources of water in the Solar System. The average D/H of carbonaceous chondrites (CC's) is known to be close to the current D/H of the Earth's ocean, while those of comets and the solar nebula are larger by about a factor of two and smaller by about a factor of seven, respectively, than that of the Earth's ocean. Thus, the main source of the Earth's ocean has been thought to be CC's or adequate mixing of comets and the solar nebula. However, those conclusions are correct only if D/H of water on the Earth has remained unchanged for the past 4.5 Gyr. In this paper, we investigate evolution of D/H in the ocean in the case that the early Earth had a hydrogen-rich atmosphere, the existence of which is predicted by recent theories of planet formation no matter whether the nebula remains or not. Then we show that D/H in the ocean increases by a factor of 2-9, which is caused by the mass fractionation during atmospheric hydrogen loss, followed by deuterium exchange between hydrogen gas and water vapor during ocean formation. This result suggests that the apparent similarity in D/H of water between CC's and the current Earth's ocean does not necessarily support the CC's origin of water and that the apparent discrepancy in D/H is not a good reason for excluding the nebular origin of water. Author Affiliation: (a) Research Center for the Evolving Earth and Planets, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan (b) Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan Article History: Received 3 August 2006; Revised 9 July 2007

When a giant impact occurs, atmosphere loss may occur due to global ground motion excited by a strong shock wave traveling in the planetary interior. Here, the relations between the ground motion and the amount of the lost atmosphere are systematically investigated through calculations of a spherically one-dimensional atmospheric motion for various initial atmospheric conditions. The fraction of the lost atmosphere to the total mass of the atmosphere is found to be controlled only by the ground velocity and, insensitive to the initial atmospheric conditions. Unlike the previous studies (Ahrens, 1990, Origin of the Earth, H.E. Newson, J.H. Jones (Eds.), pp. 211-227; Ahrens, 1993, Annu. Rev. Earth Planet. Sci. 21,525-555; Chen and Ahrens, 1997, Phys. Earth Planet. Inter. 100, 21-26); the estimated loss fraction for the giant impact is only 20%. Significant escape occurs only when the ground velocity is close to the escape velocity. Thus, most of the atmosphere should survive the giant impact. The cause of the difference from previous estimates is discussed from energetic and dynamic points of view. Moreover, if our estimates are applied to the atmosphere of the impactor planet, a significant fraction of it is carried to the target planet. Survival of the proto-atmosphere has very important effects on the origin and evolution of the terrestrial planets' volatile budget. Keywords: Atmospheres, evolution; Atmospheres, dynamics; Accretion; Terrestrial planets; Planetary formation

During planet formation, numerous small impacting bodies result in cratering impacts on large target bodies. A fraction of the target surface is eroded, while a fraction of the impactor material accretes onto the surface. These fractions depend upon the impact velocities, the impact angles, and the escape velocities of the target. This study uses smoothed particle hydrodynamics simulations to model cratering impacts onto a planar icy target for which gravity is the dominant force and material strength is neglected. By evaluating numerical results, scaling laws are derived for the escape mass of the target material and the accretion mass of the impactor material onto the target surface. Together with recently derived results for rocky bodies in a companion study, a conclusion is formulated that typical cratering impacts on terrestrial planets, except for those on Mercury, led to a net accretion, while those on the moons of giant planets, e.g., Rhea and Europa, led to a net erosion. Our newly derived scaling laws would be useful for predicting the erosion of the target body and the accretion of the impactor for a variety of cratering impacts that would occur on large rocky and icy planetary bodies during planet formation and collisional evolution from ancient times to today. [ABSTRACT FROM AUTHOR]

An accurate understanding of the relationship between the impact conditions and the degree of shock‐induced thermal metamorphism in meteorites allows the impact environment in the early Solar System to be understood. A recent hydrocode has revealed that impact heating is much higher than previously thought. This is because plastic deformation of the shocked rocks causes further heating during decompression, which is termed post‐shock heating. Here we compare impact simulations with laboratory experiments on the impact devolatilization of calcite to investigate whether the post‐shock heating is also significant in natural samples. We calculated the mass of CO2 produced from the calcite, based on thermodynamics. We found that iSALE can reproduce the devolatilization behavior for rocks with the strength of calcite. In contrast, the calculated masses of CO2 at lower rock strengths are systematically smaller than the experimental values. Our results require a reassessment of the interpretation of thermal metamorphism in meteorites. Plain Language Summary: Shock‐induced thermal metamorphism found in meteorites could be used as "the Rossetta stone," which records the ancient impact environment in the Solar System. If we could understand impact heating, then it would be possible to decode the impact history of the Solar System. We show that the temperature increase after impact events is much higher than conventionally thought, if we consider a recently realized heat source, that is post‐shock heating due to shear deformation. Impact simulations were compared with a previous experiment on the impact devolatilization of natural calcite marble to explore the influence of shear deformation on heating. The simulation reproduces the devolatilization behavior of calcite with increasing impact velocity, which demonstrates that heating due to plastic deformation is also significant in natural samples as shown in idealized numerical models. This finding suggests that mutual collisions between planetesimals, which are parent bodies of meteorites, could much easily produce shock‐induced thermal metamorphism in rocky materials than previously expected. Consequently, our Solar system might not have a number of dynamically excited bodies. Key Points: A numerical model was developed to describe impact devolatilization of calcite by taking strength effect on impact heating into accountThe mass of CO2 due to impact devolatilization in the numerical model was compared with that in a previous impact experimentThe numerical model with material strength reproduces CO2 devolatilization behavior with increasing impact velocity [ABSTRACT FROM AUTHOR]

An accurate understanding of the relationship between the impact conditions and the degree of shock‐induced thermal metamorphism in meteorites allows the impact environment in the early Solar System to be understood. A recent hydrocode has revealed that impact heating is much higher than previously thought. This is because plastic deformation of the shocked rocks causes further heating during decompression, which is termed post‐shock heating. Here we compare impact simulations with laboratory experiments on the impact devolatilization of calcite to investigate whether the post‐shock heating is also significant in natural samples. We calculated the mass of CO2 produced from the calcite, based on thermodynamics. We found that iSALE can reproduce the devolatilization behavior for rocks with the strength of calcite. In contrast, the calculated masses of CO2 at lower rock strengths are systematically smaller than the experimental values. Our results require a reassessment of the interpretation of thermal metamorphism in meteorites. Plain Language Summary: Shock‐induced thermal metamorphism found in meteorites could be used as "the Rossetta stone," which records the ancient impact environment in the Solar System. If we could understand impact heating, then it would be possible to decode the impact history of the Solar System. We show that the temperature increase after impact events is much higher than conventionally thought, if we consider a recently realized heat source, that is post‐shock heating due to shear deformation. Impact simulations were compared with a previous experiment on the impact devolatilization of natural calcite marble to explore the influence of shear deformation on heating. The simulation reproduces the devolatilization behavior of calcite with increasing impact velocity, which demonstrates that heating due to plastic deformation is also significant in natural samples as shown in idealized numerical models. This finding suggests that mutual collisions between planetesimals, which are parent bodies of meteorites, could much easily produce shock‐induced thermal metamorphism in rocky materials than previously expected. Consequently, our Solar system might not have a number of dynamically excited bodies. Key Points: A numerical model was developed to describe impact devolatilization of calcite by taking strength effect on impact heating into accountThe mass of CO2 due to impact devolatilization in the numerical model was compared with that in a previous impact experimentThe numerical model with material strength reproduces CO2 devolatilization behavior with increasing impact velocity [ABSTRACT FROM AUTHOR]

Numerous small bodies inevitably lead to cratering impacts on large planetary bodies during planet formation and evolution. As a consequence of these small impacts, a fraction of the target material escapes from the gravity of the large body, and a fraction of the impactor material accretes onto the target surface, depending on the impact velocities and angles. Here, we study the mass of the high-speed ejecta that escapes from the target gravity by cratering impacts when material strength is neglected. We perform a large number of cratering impact simulations on a planar rocky target using the smoothed particle hydrodynamics method. We show that the escape mass of the target material obtained from our numerical simulations agrees with the prediction of a scaling law under a point-source assumption when vimp ≳ 12vesc, where vimp is the impact velocity and vesc is the escape velocity of the target. However, we find that the point-source scaling law overestimates the escape mass up to a factor of ∼70, depending on the impact angle, when vimp ≲ 12vesc. Using data obtained from numerical simulations, we derive a new scaling law for the escape mass of the target material for vimp ≲ 12vesc. We also derive a scaling law that predicts the accretion mass of the impactor material onto the target surface upon cratering impacts by numerically evaluating the escape mass of the impactor material. Our newly derived scaling laws are useful for predicting the escape mass of the target material and the accretion mass of the impactor material for a variety of cratering impacts that would occur on large planetary bodies during planet formation. [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]

Throughout the history of the solar system, Mars has experienced continuous asteroidal impacts. These impacts have produced impact-generated Mars ejecta, and a fraction of this debris is delivered to Earth as Martian meteorites. Another fraction of the ejecta is delivered to the moons of Mars, Phobos and Deimos. Here, we studied the amount and condition of recent delivery of impact ejecta from Mars to its moons. Using state-of-the-art numerical approaches, we report, for the first time, that materials delivered from Mars to its moons are physically and chemically different from the Martian meteorites, which are all igneous rocks with a limited range of ages. We show that Mars ejecta mixed in the regolith of its moons potentially covers all its geological eras and consists of all types of rocks, from sedimentary to igneous. A Martian moons sample-return mission will bring such materials back to Earth, and the samples will provide a wealth of "time-resolved" geochemical information about the evolution of Martian surface environments. [ABSTRACT FROM AUTHOR]

Melting experiments were performed on the Fe‐C‐H system to 127 GPa in a laser‐heated diamond anvil cell. On the basis of in situ and ex situ sample characterizations, we found that the solubility of carbon in liquid Fe correlates inversely with hydrogen concentration at ~60 GPa and ~3500 K, indicating that liquid Fe preferentially incorporates hydrogen rather than carbon under conditions with abundant C and H. While large amounts of both C and H may have been delivered to the growing Earth, C‐poor/H‐rich metals were likely added to the protocore in the late stages of core formation. We also obtained a melting curve of FeHx (x > 1) far beyond the pressure range in earlier determinations. Its liquidus temperature was found to be 2380 K at 135 GPa, lower than those of Fe alloyed with the other possible core light elements. Relatively low core temperature is thus supported by the presence of hydrogen. Plain Language Summary: Both carbon and hydrogen are possible major light elements in the core but estimation of their abundance in the core as well as in the bulk Earth is difficult because of their high volatility. In addition, the property of hydrogen‐bearing iron alloys has been the least studied. Here we performed melting experiments on Fe‐C‐H to 127 GPa, close to the pressure at the top of the Earth's core. Our main finding is that hydrogen limits the solubility of carbon in liquid Fe; the carbon content correlates inversely with hydrogen concentration in molten Fe coexisting with diamonds at ~60 GPa and ~3500 K. Recent planet formation theories suggest that large amounts of C and H were delivered to the growing Earth. In the late stages of core formation, liquid metals preferentially incorporating hydrogen rather than carbon may have added to the protocore. We also found that hydrogen decreases the melting temperature of Fe remarkably. The melting temperature of FeHx (x > 1) is only about 2380 K at the core‐mantle boundary; lower than those of Fe‐Fe3S eutectic and Fe alloyed with the other possible core light elements. Key Points: Melting experiments on the Fe‐C‐H system were performed to 127 GPaHydrogen limits the solubility of carbon in liquid ironMelting temperature of FeHx (x > 1) is about 2380 K at 135 GPa, lower than those of Fe alloyed with the other possible core light elements [ABSTRACT FROM AUTHOR]