High pressure-temperature experiments provide information on the phase diagrams and physical characteristics of matter at extreme conditions and offer a synthesis pathway for novel materials with useful properties. Experiments recreating the conditions of planetary interiors provide important constraints on the physical properties of constituent phases and are key to developing models of planetary processes and interpreting geophysical observations. The laser-heated diamond anvil cell (DAC) is currently the only technique capable of routinely accessing the Earth's lower-mantle geotherm for experiments on non-metallic samples, but large temperature uncertainties and poor temperature stability limit the accuracy of measured data and prohibits analyses requiring long acquisition times. We have developed a novel internal resistive heating (IRH) technique for the DAC and demonstrate stable heating of non-metallic samples up to 3000 K and 64 GPa, as confirmed by in situ synchrotron x-ray diffraction and simultaneous spectroradiometric temperature measurement. The temperature generated in our IRH-DAC can be precisely controlled and is extremely stable, with less than 20 K variation over several hours without any user intervention, resulting in temperature uncertainties an order of magnitude smaller than those in typical laser-heating experiments. Our IRH-DAC design, with its simple geometry, provides a new and highly accessible tool for investigating materials at extreme conditions. It is well suited for the rapid collection of high-resolution P-V-T data, precise demarcation of phase boundaries, and experiments requiring long acquisition times at high temperature. Our IRH technique is ideally placed to exploit the move toward coherent nano-focused x-ray beams at next-generation synchrotron sources. (C) 2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution

Volcanoes produce widely varying seismic signals due to the presence of complex and non-linear physical processes. The temporal distribution of seismicity at volcanoes ranges from individual transients to swarms of many small events and protracted volcanic tremor. The spectral range of volcanic signals is unequivocally broadband, with coincident high (>20 Hz) and very low (down to periods of hundreds of seconds) frequency signals frequently observed at many volcanic systems. As such, interpretations of volcano-seismic source and process require suitable characterisation in the time-frequency (T-F) domain. The adoption of automated approaches to routine seismic processing at volcanoes also creates the need to evaluate how we suitably extract discriminatory features of interest from such diverse volcano-seismic signals.

We explore the transit timing variations (TTVs) of the young (22 Myr) nearby AU Mic planetary system. For AU Mic b, we introduce three Spitzer (4.5 mu m) transits, five TESS transits, 11 LCO transits, one PEST transit, one Brierfield transit, and two transit timing measurements from Rossiter-McLaughlin observations; for AU Mic c, we introduce three TESS transits. We present two independent TTV analyses. First, we use EXOFASTv2 to jointly model the Spitzer and ground-based transits and obtain the midpoint transit times. We then construct an O - C diagram and model the TTVs with Exo-Striker. Second, we reproduce our results with an independent photodynamical analysis. We recover a TTV mass for AU Mic c of 10.8(-2.2)(+2.3) M-circle plus. We compare the TTV-derived constraints to a recent radial velocity (RV) mass determination. We also observe excess TTVs that do not appear to be consistent with the dynamical interactions of b and c alone or due to spots or flares. Thus, we present a hypothetical nontransiting "middle-d" candidate exoplanet that is consistent with the observed TTVs and candidate RV signal and would establish the AU Mic system as a compact resonant multiplanet chain in a 4:6:9 period commensurability. These results demonstrate that the AU Mic planetary system is dynamically interacting, producing detectable TTVs, and the implied orbital dynamics may inform the formation mechanisms for this young system. We recommend future RV and TTV observations of AU Mic b and c to further constrain the masses and confirm the existence of possible additional planet(s).

We present a uniform analysis of transit observations from the Hubble Space Telescope and Spitzer Space Telescope of two warm gas giants orbiting K-type stars-WASP-29b and WASP-80b. The transmission spectra, which span 0.4-5.0 mu m, are interpreted using a suite of chemical equilibrium PLATON atmospheric retrievals. Both planets show evidence of significant aerosol opacity along the day-night terminator. The spectrum of WASP-29b is flat throughout the visible and near-infrared, suggesting the presence of condensate clouds extending to low pressures. The lack of spectral features hinders our ability to constrain the atmospheric metallicity and C/O ratio. In contrast, WASP-80b shows a discernible, albeit muted H2O absorption feature at 1.4 mu m, as well as a steep optical spectral slope that is caused by fine-particle aerosols and/or contamination from unocculted spots on the variable host star. WASP-80b joins the small number of gas-giant exoplanets that show evidence for enhanced atmospheric metallicity: the transmission spectrum is consistent with metallicities ranging from similar to 30-100 times solar in the case of cloudy limbs to a few hundred times solar in the cloud-free scenario. In addition to the detection of water, we infer the presence of CO2 in the atmosphere of WASP-80b based on the enhanced transit depth in the Spitzer 4.5 mu m bandpass. From a complementary analysis of Spitzer secondary eclipses, we find that the dayside emission from WASP-29b and WASP-80b is consistent with brightness temperatures of 937 +/- 48 and 851 +/- 14 K, respectively, indicating relatively weak day-night heat transport and low Bond albedo.

Diamond-hosted majoritic garnet inclusions provide unique insights into the Earth's deep, and otherwise inaccessible, mantle. Compared with other types of mineral inclusions found in sub-lithospheric diamonds, majoritic garnets can provide the most accurate estimates of diamond formation pressures because laboratory experiments have shown that garnet chemistry varies strongly as a function of pressure. However, evaluation using a compilation of experimental data demonstrates that none of the available empirical barometers are reliable for predicting the formation pressure of many experimental majoritic garnets and cannot be applied with confidence to diamond-hosted garnet inclusions. On the basis of the full experimental data set, we develop a novel type of majorite barometer using machine learning algorithms. Cross validation demonstrates that Random Forest Regression allows accurate prediction of the formation pressure across the full range of experimental majoritic garnet compositions found in the literature. Applying this new barometer to the global database of diamond-hosted inclusions reveals that their formation occurs in specific pressure modes. However, exsolved clinopyroxene components that are often observed within garnet inclusions are not included in this analysis. Reconstruction of inclusions, in the 8 cases where this is currently possible, reveals that ignoring small exsolved components can lead to underestimating inclusion pressures by up to 7 GPa (similar to 210 km). The predicted formation pressures of majoritic garnet inclusions are consistent with crystallization of carbon-rich slab-derived melts in Earth's deep upper mantle and transition zone.

Magma intrusion rate is a key parameter in eruption triggering but is poorly quantified in existing geodetic studies. Here we examine two episodes of rapid inflation in this context. Two noneruptive microseismic swarms were recorded at Semisopochnoi Volcano, Alaska in 2014-2015. We use differential SAR techniques and TerraSAR-X images to document surface deformation from 2011 to 2015, which comprises island-wide radial inflation totaling similar to 25 cm (+/-1 cm) line of sight displacement in 2014-2015. Multiple source geometries are tested in an inversion of the deformation data, and InSAR data are best fit by a spheroid trending to the northeast and plunging to the southeast, with a major axis of similar to 4 km and minor axes of similar to 1 km, directly under the central caldera of Semisopochnoi. In 2014, a modeled influx of 0.043 km(3) of magma caused line of sight displacement of similar to 17 cm. This magma was stored at a depth of similar to 8 km, until 2015 when 0.029 km(3) was added. Along with the definition of inflation source parameters, the recorded seismic events are relocated using differential travel times. These relocated events outline a linear aseismic area within a larger zone of shallow (<10 km) seismicity. This aseismic region aligns with the centroid of the deformation model. Based on these geodetic and seismic models, the plumbing system at Semisopochnoi is interpreted as a spheroidal magma storage zone at a depth of similar to 8 km below a linear feature of partial melt. The observed deformation and seismicity appear to result from rapid injection into this main storage region.

Pluto, Titan, and Triton make up a unique class of solar system bodies, with icy surfaces and chemically reducing atmospheres rich in organic photochemistry and haze formation. Hazes play important roles in these atmospheres, with physical and chemical processes highly dependent on particle sizes, but the haze size distribution in reducing atmospheres is currently poorly understood. Here we report observational evidence that Pluto's haze particles are bimodally distributed, which successfully reproduces the full phase scattering observations from New Horizons. Combined with previous simulations of Titan's haze, this result suggests that haze particles in reducing atmospheres undergo rapid shape change near pressure levels similar to 0.5 Pa and favors a photochemical rather than a dynamical origin for the formation of Titan's detached haze. It also demonstrates that both oxidizing and reducing atmospheres can produce multi-modal hazes, and encourages reanalysis of observations of hazes on Titan and Triton.

Several hypotheses posit a link between the origin of Homo and climatic and environmental shifts between 3 and 2.5Ma. Here we report on new results that shed light on the interplay between tectonics, basin migration and faunal change on the one hand and the fate of Australopithecus afarensis and the evolution of Homo on the other. Fieldwork at the new Mille-Logya site in the Afar, Ethiopia, dated to between 2.914 and 2.443Ma, provides geological evidence for the northeast migration of the Hadar Basin, extending the record of this lacustrine basin to Mille-Logya. We have identified three new fossiliferous units, suggesting in situ faunal change within this interval. While the fauna in the older unit is comparable to that at Hadar and Dikika, the younger units contain species that indicate more open conditions along with remains of Homo. This suggests that Homo either emerged from Australopithecus during this interval or dispersed into the region as part of a fauna adapted to more open habitats.

Geophysical and geochemical evidence suggests that Earth's core is predominantly made of iron (or iron-nickel alloy) with several percent of light elements. However, Earth's solid inner core transmits shear waves at a much lower velocity than expected from mineralogical models that are consistent with geochemical constraints. Here we investigate the effect of hydrogen on the elastic properties of iron and iron-silicon alloys using ab initio molecular dynamic simulations. We find that these H-bearing alloys maintain a superionic state under inner-core conditions and that their shear moduli exhibit a strong shear softening due to the superionic effect, with a corresponding reduction in V-S. Several hcp-iron-silicon-hydrogen compositions can explain the observed density, V-P, V-S, and Poisson's ratio of the inner core simultaneously. Our results indicate that hydrogen is a significant component of the Earth's core, and that it may contain at least four ocean masses of water. This indicates that the Earth may have accreted wet and obtained its water from chondritic and/or nebular materials before or during core formation. (C) 2021 Elsevier B.V. All rights reserved.