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Carbon is the fourth-most prevalent element in the Universe and essential for all known life. In the elemental form it is found in multiple allotropes, including graphite, diamond and fullerenes, and it has long been predicted that even more structures can exist at pressures greater than those at Earth’s core 1 – 3 . Several phases have been predicted to exist in the multi-terapascal regime, which is important for accurate modelling of the interiors of carbon-rich exoplanets 4 , 5 . By compressing solid carbon to 2 terapascals (20 million atmospheres; more than five times the pressure at Earth’s core) using ramp-shaped laser pulses and simultaneously measuring nanosecond-duration time-resolved X-ray diffraction, we found that solid carbon retains the diamond structure far beyond its regime of predicted stability. The results confirm predictions that the strength of the tetrahedral molecular orbital bonds in diamond persists under enormous pressure, resulting in large energy barriers that hinder conversion to more-stable high-pressure allotropes 1 , 2 , just as graphite formation from metastable diamond is kinetically hindered at atmospheric pressure. This work nearly doubles the highest pressure at which X-ray diffraction has been recorded on any material. X-ray diffraction measurements of solid carbon compressed to pressures of about two terapascals (approximately twenty million atmospheres) find that carbon retains a diamond structure even under these extreme conditions.

In situ femtosecond X-ray diffraction measurements reveal that the dominant mechanism of shock-wave-driven deformation in tantalum changes from twinning to dislocation slip as pressure increases. Deformation caught in the act The effect of shock waves travelling through materials has relevance for various areas of study in geology and materials science. Experiments that probe how materials deform on exposure to shock waves are usually carried out in retrospect of the shock event. This paper reports in situ X-ray diffraction studies of the plastic deformation of textured polycrystalline tantalum on exposure to shock compression with shock pressures ranging from 10 gigapascals to around 300 gigapascals (at which the metal melts). Twinning and slip deformations produce distinct changes to the texture of the tantalum sample and these changes could be observed in the diffraction data. In this way, the researchers observed that the dominant deformation mechanism transitioned from minimal twinning to twinning-dominated to slip-dominated as the shock pressure increased above 150 gigapascals. This dynamic material behaviour would be challenging to observe in experiments carried out after the shock event. Pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites 1 , 2 , 3 , the formation of interstellar dust clouds 4 , ballistic penetrators 5 , spacecraft shielding 6 and ductility in high-performance ceramics 7 . At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. Experiments that characterized lattice defects 8 , 9 , 10 , 11 have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing 12 and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials 13 , but have only recently been applied to plasticity during shock compression 14 , 15 , 16 , 17 and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ , lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations 18 , 19 , 20 and experiments 8 , 9 , 10 , 11 , 12 have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks 21 , we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. The techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.

Plant-soil relations may explain why low-external input (LEI) diversified cropping systems are more efficient than their conventional counterparts. This work sought to identify links between management practices, soil quality changes, and root responses in a long-term cropping systems experiment in Iowa where grain yields of 3-year and 4-year LEI rotations have matched or exceeded yield achieved by a 2-year maize (Zea mays L.) and soybean (Glycine max L.) rotation. The 2-year system was conventionally managed and chisel-ploughed, whereas the 3-year and 4-year systems received plant residues and animal manures and were periodically moldboard ploughed. We expected changes in soil quality to be driven by organic matter inputs, and root growth to reflect spatial and temporal fluctuations in soil quality resulting from those additions. We constructed a carbon budget and measured soil quality indicators (SQIs) and rooting characteristics using samples taken from two depths of all crop-phases of each rotation system on multiple dates. Stocks of particulate organic matter carbon (POM-C) and potentially mineralizable nitrogen (PMN) were greater and more evenly distributed in the LEI than conventional systems. Organic C inputs, which were 58% and 36% greater in the 3-year rotation than in the 4-year and 2-year rotations, respectively, did not account for differences in SQI abundance or distribution. Surprisingly, SQIs did not vary with crop-phase or date. All biochemical SQIs were more stratified (p<0.001) in the conventionally-managed soils. While POM-C and PMN in the top 10 cm were similar in all three systems, stocks in the 10-20 cm depth of the conventional system were less than half the size of those found in the LEI systems. This distribution was mirrored by maize root length density, which was also concentrated in the top 10 cm of the conventionally managed plots and evenly distributed between depths in the LEI systems. The plow-down of organic amendments and manures established meaningful differences in SQIs and extended the rhizosphere of the LEI systems. Resulting efficiencies observed in the LEI grain crops indicate that resource distribution as well as abundance is an important component of soil function that helps explain how LEI systems can maintain similar or greater yields with fewer inputs than achieved by their conventional counterparts.

New laboratory techniques for applying enormous pressures allow diamond to be compressed to 50 million atmospheres, providing insight into the interiors of planets and theoretical implications. Journey to the centre of Jupiter Knowledge of the behaviour of matter under conditions of extreme pressure is essential for describing the interior state of giant planets such as Jupiter and many extrasolar planets. The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in California is pursuing laboratory astrophysics with shock-free dynamic (ramp) compression up to 50 million atmospheres pressure. Working with the NIF at temperatures below those used in fusion experiments, Raymond Smith and colleagues have achieved a new experimental benchmark in the replication of conditions deep within giant planets. They describe properties of carbon compressed to an unprecedented density of 12 g cm −3 . These results also provide some of the most direct experimental tests of quantum-statistical theories developed in the early days of quantum mechanics. The recent discovery of more than a thousand planets outside our Solar System 1 , 2 , together with the significant push to achieve inertially confined fusion in the laboratory 3 , has prompted a renewed interest in how dense matter behaves at millions to billions of atmospheres of pressure. The theoretical description of such electron-degenerate matter has matured since the early quantum statistical model of Thomas and Fermi 4 , 5 , 6 , 7 , 8 , 9 , 10 , and now suggests that new complexities can emerge at pressures where core electrons (not only valence electrons) influence the structure and bonding of matter 11 . Recent developments in shock-free dynamic (ramp) compression now allow laboratory access to this dense matter regime. Here we describe ramp-compression measurements for diamond, achieving 3.7-fold compression at a peak pressure of 5 terapascals (equivalent to 50 million atmospheres). These equation-of-state data can now be compared to first-principles density functional calculations 12 and theories long used to describe matter present in the interiors of giant planets, in stars, and in inertial-confinement fusion experiments. Our data also provide new constraints on mass–radius relationships for carbon-rich planets.

There has been considerable recent interest in the high-pressure behavior of silicon carbide, a potential major constituent of carbon-rich exoplanets. In this work, the atomic-level structure of SiC was determined through in situ X-ray diffraction under laser-driven ramp compression up to 1.5 TPa; stresses more than seven times greater than previous static and shock data. Here we show that the B1-type structure persists over this stress range and we have constrained its equation of state (EOS). Using this data we have determined the first experimentally based mass-radius curves for a hypothetical pure SiC planet. Interior structure models are constructed for planets consisting of a SiC-rich mantle and iron-rich core. Carbide planets are found to be ~10% less dense than corresponding terrestrial planets. Using ramp compression, silicon carbide was compressed to pressures of 1.5 terapascals, more than seven times higher than previous work. The results show that large carbon-rich exoplanets would be ~10% less dense than corresponding rocky planets.

Investigating how solid matter behaves at enormous pressures, such as those found in the deep interiors of giant planets, is a great experimental challenge. Over the past decade, computational predictions have revealed that compression to terapascal pressures may bring about counter-intuitive changes in the structure and bonding of solids as quantum mechanical forces grow in influence 1 – 6 . Although this behaviour has been observed at modest pressures in the highly compressible light alkali metals 7 , 8 , it has not been established whether it is commonplace among high-pressure solids more broadly. We used shaped laser pulses at the National Ignition Facility to compress elemental Mg up to 1.3 TPa, which is approximately four times the pressure at the Earth’s core. By directly probing the crystal structure using nanosecond-duration X-ray diffraction, we found that Mg changes its crystal structure several times with non-close-packed phases emerging at the highest pressures. Our results demonstrate that phase transformations of extremely condensed matter, previously only accessible through theoretical calculations, can now be experimentally explored. Numerical studies have predicted that solids at extremely high pressures should exhibit changes in structure driven by quantum mechanical effects. These predictions have now been verified in magnesium.

Recent discoveries of water-rich Neptune-like exoplanets require a more detailed understanding of the phase diagram of H 2 O at pressure–temperature conditions relevant to their planetary interiors. The unusual non-dipolar magnetic fields of ice giant planets, produced by convecting liquid ionic water, are influenced by exotic high-pressure states of H 2 O—yet the structure of ice in this state is challenging to determine experimentally. Here we present X-ray diffraction evidence of a body-centered cubic (BCC) structured H 2 O ice at 200 GPa and ~ 5000 K, deemed ice XIX, using the X-ray Free Electron Laser of the Linac Coherent Light Source to probe the structure of the oxygen sub-lattice during dynamic compression. Although several cubic or orthorhombic structures have been predicted to be the stable structure at these conditions, we show this BCC ice phase is stable to multi-Mbar pressures and temperatures near the melt boundary. This suggests variable and increased electrical conductivity to greater depths in ice giant planets that may promote the generation of multipolar magnetic fields.

Little is known about the structure of possible mantle materials of extra-solar super-Earths with interior pressures of up to 1,000 GPa. Dynamic X-ray diffraction measurements of ramp-compressed magnesium oxide, an important component of Earth’s mantle, show a solid–solid state transition at about 600 GPa, with a high-pressure structure that is stable up to 900 GPa. Magnesium oxide is an important component of the Earth’s mantle and has been extensively studied at pressures and temperatures relevant to Earth 1 . However, much less is known about the behaviour of this oxide under conditions likely to occur in extrasolar planets with masses up to 10 times that of Earth, termed super-Earths, where pressures can exceed 1,000 GPa (10 million atmospheres). Magnesium oxide is expected to change from a rocksalt crystal structure (B1) to a caesium chloride (B2) structure at pressures of about 400–600 GPa (refs  2 , 3 ). Whereas no structural transformation was observed in static compression experiments up to 250 GPa (ref.  4 ), evidence for a solid–solid phase transition was obtained in shockwave experiments above 400 GPa and 9,000 K (ref.  5 ), albeit no structural measurements were made. As a result, the properties and the structure of MgO under conditions relevant to super-Earths and large planets are unknown. Here we present dynamic X-ray diffraction measurements of ramp-compressed magnesium oxide. We show that a solid–solid phase transition, consistent with a transformation to the B2 structure, occurs near 600 GPa. On further compression, this structure remains stable to 900 GPa. Our results provide an experimental benchmark to the equations of state and transition pressure of magnesium oxide, and may help constrain mantle viscosity and convection in the deep mantle of extrasolar super-Earths.

We present a method to determine the bulk temperature of a single crystal diamond sample at an X-Ray free electron laser using inelastic X-ray scattering. The experiment was performed at the high energy density instrument at the European XFEL GmbH, Germany. The technique, based on inelastic X-ray scattering and the principle of detailed balance, was demonstrated to give accurate temperature measurements, within 8 % for both room temperature diamond and heated diamond to 500 K. Here, the temperature was increased in a controlled way using a resistive heater to test theoretical predictions of the scaling of the signal with temperature. The method was tested by validating the energy of the phonon modes with previous measurements made at room temperature using inelastic X-ray scattering and neutron scattering techniques. This technique could be used to determine the bulk temperature in transient systems with a temporal resolution of 50 fs and for which accurate measurements of thermodynamic properties are vital to build accurate equation of state and transport models.