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Stability of H 3 O at extreme conditions and implications for the magnetic fields of Uranus and NeptuneThe anomalous nondipolar and nonaxisymmetric magnetic fields of Uranus and Neptune have long challenged conventional views of planetary dynamos. A thin-shell dynamo conjecture captures the observed phenomena but leaves unexplained the fundamental material basis and underlying mechanism. Here we report extensive quantum-mechanical calculations of polymorphism in the hydrogen–oxygen system at the pressures and temperatures of the deep interiors of these ice giant planets (to >600 GPa and 7,000 K). The results reveal the surprising stability of solid and fluid trihydrogen oxide (H 3 O) at these extreme conditions. Fluid H 3 O is metallic and calculated to be stable near the cores of Uranus and Neptune. As a convecting fluid, the material could give rise to the magnetic field consistent with the thin-shell dynamo model proposed for these planets. H 3 O could also be a major component in both solid and superionic forms in other (e.g., nonconvecting) layers. The results thus provide a materials basis for understanding the enigmatic magnetic-field anomalies and other aspects of the interiors of Uranus and Neptune. These findings have direct implications for the internal structure, composition, and dynamos of related exoplanets.
Sub-Neptunes are common among the discovered exoplanets. However, lack of knowledge on the state of matter in
O-rich setting at high pressures and temperatures ( ) places important limitations on our understanding of this planet type. We have conducted experiments for reactions between and O as archetypal materials for rock and ice, respectively, at high . We found anomalously expanded volumes of dense silica (up to 4%) recovered from hydrothermal synthesis above ∼24 GPa where the -type (Ct) structure appears at lower pressures than in the anhydrous system. Infrared spectroscopy identified strong OH modes from the dense silica samples. Both previous experiments and our density functional theory calculations support up to 0.48 hydrogen atoms per formula unit of ( ) . At pressures above 60 GPa, O further changes the structural behavior of silica, stabilizing a niccolite-type structure, which is unquenchable. From unit-cell volume and phase equilibrium considerations, we infer that the niccolite-type phase may contain H with an amount at least comparable with or higher than that of the Ct phase. Our results suggest that the phases containing both hydrogen and lithophile elements could bemore »
Abstract Studies of molecular mixtures containing hydrogen sulfide (H 2 S) could open up new routes towards hydrogen-rich high-temperature superconductors under pressure. H 2 S and ammonia (NH 3 ) form hydrogen-bonded molecular mixtures at ambient conditions, but their phase behavior and propensity towards mixing under pressure is not well understood. Here, we show stable phases in the H 2 S–NH 3 system under extreme pressure conditions to 4 Mbar from first-principles crystal structure prediction methods. We identify four stable compositions, two of which, (H 2 S) (NH 3 ) and (H 2 S) (NH 3 ) 4 , are stable in a sequence of structures to the Mbar regime. A re-entrant stabilization of (H 2 S) (NH 3 ) 4 above 300 GPa is driven by a marked reversal of sulfur-hydrogen chemistry. Several stable phases exhibit metallic character. Electron–phonon coupling calculations predict superconducting temperatures up to 50 K, in the Cmma phase of (H 2 S) (NH 3 ) at 150 GPa. The present findings shed light on how sulfur hydride bonding and superconductivity are affected in molecular mixtures. They also suggest a reservoir for hydrogen sulfide in the upper mantle regions of icy planets in a potentially metallic mixture, which couldmore »
The distribution and transportation of water in Earth’s interior depends on the stability of water-bearing phases. The transition zone in Earth’s mantle is generally accepted as an important potential water reservoir because its main constituents, wadsleyite and ringwoodite, can incorporate weight percent levels of H2O in their structures at mantle temperatures. The extent to which water can be transported beyond the transition zone deeper into the mantle depends on the water carrying capacity of minerals stable in subducted lithosphere. Stishovite is one of the major mineral components in subducting oceanic crust, yet the capacity of stishovite to incorporate water beyond at lower mantle conditions remains speculative. In this study, we combine in situ laser heating with synchrotron X-ray diffraction to show that the unit cell volume of stishovite synthesized under hydrous conditions is ∼2.3 to 5.0% greater than that of anhydrous stishovite at pressures of ∼27 to 58 GPa and temperatures of 1,240 to 1,835 K. Our results indicate that stishovite, even at temperatures along a mantle geotherm, can potentially incorporate weight percent levels of H2O in its crystal structure and has the potential to be a key phase for transporting and storing water in the lower mantle.
Thermonuclear Supernovae (SNe Ia) are one of the building blocks of modern cosmology and laboratories for the explosion physics of White Dwarf star/s (WD) in close binary systems. The second star may be aWD(double degenerate systems, DD), or a non-degenerated star (SD) with a main sequence star, red giant or a helium star as companion (Branch et al. 1995; Nomoto et al. 2003; Wang & Han 2012). Light curves and spectra of the explosion look similar because a ’stellar amnesia’ (H¨oflich et al. 2006). Basic nuclear physics determines the progenitor structure and the explosion physics, breaking the link between progenitor evolution, and the explosion, resulting in three main classes of explosion scenarios: a) dynamical merging of two WD and a heating on time scales of seconds (Webbink 1984; Isern et al. 2011), b) surface helium detonations on top of a WD which ignite the central C/O by a detonation wave traveling inwards (Nomoto 1982; Hoeflich & Khokhlov 1996; Kromer et al. 2010); c) compressional heating in an accreting WD approaching the Chandrasekar mass on time of up to 108 years which may originated from SD and DD systems (Whelan & Iben 1973; Piersanti et al. 2003). Simulations of the explosionsmore »