Icy Material Research Articles

Possible Carbon Dioxide above the Thick Aerosols of GJ 1214 b

Sub-Neptune planets with radii smaller than Neptune (3.9 R ⊕) are the most common type of planet known to exist in the Milky Way, even though they are absent in the solar system. These planets can potentially have a large diversity of compositions as a result of different mixtures of rocky material, icy material, and gas accreted from a protoplanetary disk. However, the bulk density of a sub-Neptune, informed by its mass and radius alone, cannot uniquely constrain its composition; atmospheric spectroscopy is necessary. GJ 1214 b, which hosts an atmosphere that is potentially the most favorable for spectroscopic detection of any sub-Neptune, is instead enshrouded in aerosols (thus showing no spectroscopic features), hiding its composition from view at previously observed wavelengths in its terminator. Here, we present a JWST NIRSpec transmission spectrum from 2.8 to 5.1 μm that shows signatures of CO2 and CH4, expected at high metallicity. A model containing both these molecules is preferred by 3.3σ and 3.6σ as compared to a featureless spectrum for two different data analysis pipelines, respectively. Given the low signal-to-noise of the features compared to the continuum, however, more observations are needed to confirm the CO2 and CH4 signatures and better constrain other diagnostic features in the near-infrared. Further modeling of the planet’s atmosphere, interior structure and origins will provide valuable insights about how sub-Neptunes like GJ 1214 b form and evolve.

Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Material during the Nice Model Migration

In the Nice model of Solar System formation, Uranus and Neptune undergo an orbital upheaval, sweeping through a planetesimal disk. The region of the disk from which material is accreted by the ice giants during this phase of their evolution has not previously been identified. We perform direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment event, with collision rates as high as ∼3 per hour assuming km-sized planetesimals, increasing the total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the largest total enhancement. We determine that, for some plausible planetesimal properties, the resulting atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling timescale according to existing models. Our findings suggest that substantial accretion during this phase of planetary evolution may have been sufficient to impact the atmospheric composition and thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.

A review on the preparation techniques and geotechnical behaviour of icy lunar regolith simulants

This review provides an in-depth analysis of the methods used to produce icy regolith simulants with a focus on the Moon. Current knowledge of the form and morphology of ice on the Moon is limited, yet a wide range of studies have used ice and regolith analogues to simulate the icy material in lunar cold traps. The physical properties of ice on the Moon may vary significantly depending on its form as either an amorphous or crystalline solid, as well as its physical texture with lunar regolith. As a result, the choice of a particular preparation technique used to create an icy regolith simulant may directly impact the results of a study. It is found that sample preparation techniques can be broadly classified based on the mechanism of ice formation, proposed as either the freezing of liquid to solid, direct deposition (desublimation) of vapor to solid, or the comminution of large blocks to smaller fragments. Secondary growth structures including re-cementation, vapor re-deposition or ductile deformation of ice can also be achieved by post-processing techniques like thermal or pressure-induced metamorphism of the ice. Differences in the form and morphology of icy regolith is also found to significantly influence geotechnical behaviour to a greater extent than changes in ice content, bulk density or temperature. Specifically, vapor-deposited and amorphous ices which best simulate the formation conditions of ice on the Moon are the weakest, whilst ice-cemented ’mud-pies’ which are commonly produced by gradually freezing simulant mixtures containing liquid water, which is not stable on the Moon, can be orders of magnitude stronger. The limitations of current simulants are highlighted, and several opportunities to combine or improve existing techniques are provided. In conclusion, further study using techniques that involve comminution and deposition of ice in the absence of the liquid phase of water are recommended to better emulate the formation and weathering pathways of icy regolith on the Moon, and ultimately its physical properties.

Pore Accessibility in Amorphous Solid Water

The porous nature of amorphous solid water (ASW) can significantly effect the chemical evolution of any planetary or astrophysical surface it forms on due to its ability to trap and retain volatiles. The amount of volatiles that can enter an ASW grain or mantle is limited by how interconnected the pores are to each other and to the exterior surface. Previous laboratory studies examined the interconnectivity of ASW pores in thin ASW films relevant to ice mantles on interstellar grains. Here, we investigate to what extent the interconnectivity of pores and subsequent gas absorption properties of ASW change as one moves toward thicker samples (up to ∼1019 H2O cm−2 or ∼4 μm) more representative of icy material found in the outer solar system. We find that for all film thicknesses studied, the internal pores are accessible from the sample’s surface, and the amount of gas needed to fill the pores increases linearly with the ASW column density. This linear relation supports that the interconnectivity to the surface will persist in ices that are much thicker than those we were able to study, suggesting that the amount of contaminant gas trapped within ASW can significantly alter the chemical evolution of a variety of ASW-rich surfaces in the outer solar system.

First principles molecular dynamics study of proton disorder in [formula omitted] phase of H2 hydrate

The proton-disordered and -ordered crystal structures proposed based on X-ray diffraction experiments for the C1′ phase of H2 hydrate were investigated using first-principles (FP) path-integral ring-polymer molecular dynamics (RPMD) simulations. Our simulated Raman spectra obtained from the FP-RPMD trajectories provide unambiguous evidence for static orientational disorder of H2O molecules forming stacked H-bonded rings. This feature is essential to reproduce the characteristics of the observed Raman spectra. Furthermore, the present study shows that van der Waals interactions need to be treated carefully to achieve satisfactory computational results. The findings of this study can help for better understanding of icy materials.

Formation of super-Earths in icy dead zones around low-mass stars

ABSTRACT While giant planet occurrence rates increase with stellar mass, occurrence rates of close-in super-Earths decrease. This is in contradiction to the expectation that the total mass of the planets in a system scale with the protoplanetary disc mass and hence the stellar mass. Since the snow line plays an important role in the planet formation process, we examine differences in the temperature structure of protoplanetary gas discs around stars of different mass. Protoplanetary discs likely contain a dead zone at the mid-plane that is sufficiently cold and dense for the magneto-rotational instability to be suppressed. As material builds up, the outer parts of the dead zone may be heated by self-gravity. The temperature in the disc can be below the snow line temperature far from the star and in the inner parts of a dead zone. The inner icy region has a larger radial extent around smaller mass stars. The increased mass of solid icy material may allow for the in situ formation of larger and more numerous planets close to a low-mass star. Super-Earths that form in the inner icy region may have a composition that includes a significant fraction of volatiles.

Infrared spectra of complex organic molecules in astronomically relevant ice mixtures

Context. The increasing sensitivity and resolution of ground-based telescopes have enabled the detection of gas-phase complex organic molecules (COMs) across a variety of environments. Many of the detected species are expected to form on the icy surface of interstellar grains and transfer later into the gas phase. Therefore, icy material is regarded as a primordial source of complex molecules in the interstellar medium. Upcoming James Webb Space Telescope (JWST) observations of interstellar ices in star-forming regions will reveal infrared (IR) features of frozen molecules with unprecedented resolution and sensitivity. To identify COM features in the JWST data, laboratory IR spectra of ices for conditions that simulate interstellar environments are needed. Aims. This work provides laboratory mid-IR spectra of methyl cyanide (CH3CN, also known as acetonitrile) ice in its pure form and mixed with known interstellar molecules at cryogenic temperatures. The spectroscopic data presented in this work will support the interpretation of JWST ice observations and are made available to the community through the Leiden Ice Database for Astrochemistry (LIDA). Methods. Fourier transform IR spectroscopy is used to record the mid-IR spectra (500–4000 cm−1/20–2.5 µm, with a resolution of 1 cm−1 ) of methyl cyanide (acetonitrile, CH3 CN) mixed with H2O, CO, CO2, CH4, NH3, H2O:CO2, and H2O:CH4:NH3, at temperatures ranging from 15 to 150 K. The refractive index (at 632.8 nm) of pure amorphous CH3CN ice at 15 K and the band strength of selected IR transitions are also measured. Results. We present a variety of reference mid-IR spectra of frozen CH3CN that can be compared to astronomical ice observations. The peak position and full width at half maximum (FWHM) of six absorption bands of frozen methyl cyanide in its pure form and mixed ices, at temperatures between 15–150 K, are characterized. These bands are the following: the CH3 symmetric stretching at 2940.9 cm−1 (3.400 µm), the CN stretching at 2252.2 cm−1 (4.440 µm), a peak resulting from a combination of different vibrational modes at 1448.3 cm−1 (6.905 µm), the CH3 antisymmetric deformation at 1410 cm−1 (7.092 µm), the CH3 symmetric deformation at 1374.5 cm−1 (7.275 um), and the CH3 rock vibration at 1041.6 cm−1 (9.600 um). Additionally, the apparent band strength of these vibrational modes in mixed ices is derived. The laboratory spectra of CH3CN are compared to observations of interstellar ices toward W33A and three low-mass Young Stellar Objects (YSO). Since an unambiguous identification of solid methyl cyanide toward these objects is not possible, upper limits for the CH3CN column density are determined as ≤2.4 × 1017 molecules cm−2 for W33A and 5.2 × 1016, 1.9 × 1017, and 3.8 × 1016 molecules cm−2 for EC92, IRAS 03235, and L1455 IRS3, respectively. With respect to solid H2O, these values correspond to relative abundances of 1.9, 3.1, 1.3, and 4.1%, for W33A, EC92, IRAS 03235, and L1455 IRS3, respectively.

Let It Go: Geophysically Driven Ejection of the Haumea Family Members

We present a new model for Haumea’s formation and evolution that relies on geophysical and geochemical data informed from observations of Haumea and meteorites to explain the characteristics of Haumea and its dynamical family. We hypothesize that after the impact of two partially differentiated Kuiper Belt objects, Haumea’s rocky core grew, decreasing its moment of inertia (MOI), spinning it up to the point that icy material was ejected from its surface. This ice, carrying about 3% of Haumea’s mass and 14% of its initial angular momentum, comprises the Haumean dynamical family and the ring system and moons observed today. Later, melted ice hydrated Haumea’s core and it grew, increasing Haumea’s MOI and spinning it down to the modern value. We use the geophysical code kyushu to demonstrate that solutions exist for a Haumea in hydrostatic equilibrium at each of these hypothesized stages. Geochemical modeling using the IcyDwarf code constrains the formation of Haumea’s core and the creation of the collision family to have occurred after roughly 150–160 Myr of solar system evolution (4.41 ± 0.01 Gyr ago). Hydration of the core was complete by about 0.20 Gyr, but a substantial subsurface ocean with half the mass of Earth’s oceans persisted until it froze at about 0.45 Gyr, making Haumea the solar system’s most distant potential relict ocean world.

A Pluto–Charon Sonata IV. Improved Constraints on the Dynamical Behavior and Masses of the Small Satellites

We discuss a new set of ∼500 numerical n-body calculations designed to constrain the masses and bulk densities of Styx, Nix, Kerberos, and Hydra. Comparisons of different techniques for deriving the semimajor axis and eccentricity of the four satellites favor methods relying on the theory of Lee & Peale, where satellite orbits are derived in the context of the restricted three-body problem (Pluto, Charon, and one massless satellite). In each simulation, we adopt the nominal satellite masses derived in Kenyon & Bromley, multiply the mass of at least one satellite by a numerical factor f ≥ 1, and establish whether the system ejects at least one satellite on a timescale ≤4.5 Gyr. When the total system mass is large (f ≫ 1), ejections of Kerberos are more common. Systems with lower satellite masses (f ≈ 1) usually eject Styx. In these calculations, Styx often “signals” an ejection by moving to higher orbital inclination long before ejection; Kerberos rarely signals in a useful way. The n-body results suggest that Styx and Kerberos are more likely to have bulk densities comparable with water ice, ρ SK ≲ 2 g cm−3, than with rock. A strong upper limit on the total system mass, M SNKH ≲ 9.5 × 1019 g, also places robust constraints on the average bulk density of the four satellites, ρ SNKH ≲ 1.4 g cm−3. These limits support models where the satellites grow out of icy material ejected during a major impact on Pluto or Charon.

ENIGMATIC NEBULOUS COMPANIONS TO THE GREAT SEPTEMBER COMET OF 1882 AS SOHO-LIKE KREUTZ SUNGRAZERS CAUGHT IN TERMINAL OUTBURST

I investigate the nature of the transient nebulous companions to the sungrazing comet C/1882 R1, known as the Great September Comet. The features were located several degrees to the southwest of the comet's head and reported independently by four observers, including J.F.J. Schmidt and E.E. Barnard, over a period of ten days nearly one month after perihelion, when the comet was 0.7 AU to 1 AU from the Sun. I conclude that none of the nebulous companions was ever sighted more than once and that, contrary to his belief, Schmidt observed unrelated objects on the four consecutive mornings. Each nebulous companion is proposed to have been triggered by a fragment at most a few tens of meters across, released from the comet's nucleus after perihelion and seen only because it happened to be caught in the brief terminal outburst, when its mass was suddenly shattered into a cloud of mostly microscopic debris due possibly to rotational bursting triggered by sublimation torques. The fragment's motion was affected by a strong outgassing-driven nongravitational acceleration with a significant out-of-plane component. Although fragmentation events were common, only a small fraction of nebulous companions was detected because of their transient nature. The observed brightness of the nebulous companions is proposed to have been due mainly to C2 emissions, with a contribution from scattering of sunlight by the microscopic dust. By their nature, the fragments responsible for the nebulous companions bear a strong resemblance to the dwarf Kreutz sungrazers detected with the coronagraphs aboard the SOHO space probe. Only their fragmentation histories are different and the latter display no terminal outburst, a consequence of extremely short lifetimes of the sublimating icy and refractory material in the Sun's corona.

Elasticity of selected icy satellite candidate materials (CO2, C6H6, MgSO4·7H2O and CaSO4·2H2O) revisited by dispersion corrected density functional theory

Seismic studies are essential for accurate characterisation of planetary interior structures, but are dependent on modelling for interpretation, requiring data on the elastic properties of likely constituent minerals. With the potential deployment of seismic stations on icy worlds such as Europa and Titan envisioned for the near future, a campaign of study into the elasticity of potential icy ocean world minerals is of paramount importance.In the paper we assess the role of first-principles computer simulations to this problem, in particular focussing on the application of recent advances in simulating dispersion forces in loosely-bonded molecular solids, likely to be the main constituents of icy ocean worlds. This is of particular interest for these kinds of materials, since the complex sample handling, phase transitions and the difficulty of obtaining single crystals often greatly complicates the experimental determination of the full elastic tensor.We focus on CO2, C6H6, MgSO4·7H2O and CaSO4·2H2O as they allow us to benchmark the performance over a wide range of chemical space, structural topologies, crystal symmetries and bonding types, and moreover have accurate experimentally determined unit-cell dimensions, bulk moduli and full elastic tensors for benchmarking purposes.We demonstrate that the dispersion corrected approaches indeed perform better in modelling the experimental density profiles (mean unsigned differences of only 0.04 g/cm3 (CO2), 0.02 g/cm3 (C6H6), 0.003 g/cm3 (MgSO4·7H2O) and 0.013 g/cm3 (CaSO4·2H2O)) and may find application in exploring the compressive parameters of candidate materials, which could then be used in rheological models of icy ocean worlds.Moreover, we have assessed if the elastic constants computed by dispersion corrected density functional theory are accurate enough to be used in a reference data base for the seismic exploration of icy ocean worlds. Despite one approach having demonstrated good accuracy compared with the experimental values in modelling the elasticity of CO2, we instead find average differences from expected P and S wave velocities of around 10 to 25% for the elastically more complex title compounds. In part these differences are due to the large temperature difference between the experimental elasticity data (typically near 300 K) and our calculations, which were performed in the athermal limit.

Preparation of Titanium Dioxide Nanotube-Based Dental Implants for Osteogenesis and Osseointegration Acceleration

Dentition defects or missing are common diseases threatening human health. The dental implant technology is an effective way to repair dentition defects. Titanium and titanium alloy implants are widely used in clinical practice because of their good biocompatibility, corrosion resistance, and high mechanical strength. In this study, anodic oxidation was used to prepare titanium dioxide nanotubes with different diameters. Due to the strong adsorption capacity of the nanotube structure, the nanotube was loaded with icariin, and then the titanium dioxide nanotubes loaded with icariin (NTx + ICy) were applied in osteogenesis and osseointegration experiment. It was found that the prepared titanium dioxide nanotube wall was smooth. The diameters of the nanotubes prepared at 10 V, 20 V, and 28 V were 30 nm, 50 nm and 75 nm, respectively. The proportion of icariin was varied, and the most sustained release time of icariin was three days, and the sustained release amount was relatively large on the first day. At each time point, the number of cells adhered to the pure titanium sheets and 10 V-treated nanotubes-Icariin was large and notably higher than 30 V-treated nanotube-Icariin. The patients involved were subjected to puncture to obtain bone marrow stem cells. It was found that the NTx + ICy materials promoted the osteoblast proliferation. Further, clinical observation found that the composite titanium dioxide nanotube materials can stimulate macrophages to create a powerful bone immune microenvironment and accelerate the process of osseointegration.

Structure and nature of ice XIX

Ice is a material of fundamental importance for a wide range of scientific disciplines including physics, chemistry, and biology, as well as space and materials science. A well-known feature of its phase diagram is that high-temperature phases of ice with orientational disorder of the hydrogen-bonded water molecules undergo phase transitions to their ordered counterparts upon cooling. Here, we present an example where this trend is broken. Instead, hydrochloric-acid-doped ice VI undergoes an alternative type of phase transition upon cooling at high pressure as the orientationally disordered ice remains disordered but undergoes structural distortions. As seen with in-situ neutron diffraction, the resulting phase of ice, ice XIX, forms through a Pbcn-type distortion which includes the tilting and squishing of hexameric clusters. This type of phase transition may provide an explanation for previously observed ferroelectric signatures in dielectric spectroscopy of ice VI and could be relevant for other icy materials.

Experimental investigations of thermal properties of icy lunar regolith and their influence on phase change interface movement

Heat and mass transfers occurring on surface and within subsurface of extraterrestrial bodies during natural and future industrial heating processes require knowledge of thermal properties of porous dry and icy materials. This paper investigates thermal properties of icy lunar regolith with various water ice contents and their influence on phase change interface movement. A series of experiments has been employed to simulate borehole heating of icy regolith samples under low vacuum (0.1–1.5 ​Torr) and very low temperatures (>93 ​K) using JSC-1A regolith analogs prepared as “mud-pies” with water contents from 0 to 15 ​wt%. Cylindrical samples were heated via cartridge heater located in the center of the samples. Real-time measurements of temperatures in an array of points and vacuum chamber pressures were recorded. To decipher thermal properties data in this inverse heat equation problem, a 3D finite element method modelling has been used to simulate the behaviour of both the samples and the vacuum chamber. The results provided rough matches with expected thermal properties and the model was used in determination of phase change interface movement in the samples. These results could be applicable to research on properties and composition of other rocky and icy extraterrestrial objects or design of water ice prospecting instruments. Most importantly they should improve our understanding of processes applied in extraterrestrial water mining and visualize engineering challenges of these processes.

Gas accretion damped by dust back-reaction at the snow line

Context. The water snow line divides dry and icy solid material in protoplanetary disks. It has been thought to significantly affect planet formation at all stages. If dry particles break up more easily than icy ones, then the snow line causes a traffic jam because small grains drift inward at lower speeds than larger pebbles. Aims. We aim to evaluate the effect of high dust concentrations around the snow line onto the gas dynamics. Methods. Using numerical simulations, we modeled the global radial evolution of an axisymmetric protoplanetary disk. Our model includes particle growth, the evaporation and recondensation of water, and the back-reaction of dust onto the gas. The model takes into account the vertical distribution of dust particles. Results. We find that the dust back-reaction can stop and even reverse the net flux of gas outside the snow line, decreasing the gas accretion rate onto the star to under 50% of its initial value. At the same time, the dust accumulates at the snow line, reaching dust-to-gas ratios of ɛ ≳ 0.8, and it delivers large amounts of water vapor towards the inner disk as the icy particles cross the snowline. However, the accumulation of dust at the snow line and the decrease in the gas accretion rate only take place if the global dust-to-gas ratio is high (ε0 ≳ 0.03), the viscous turbulence is low (αν ≲ 10−3), the disk is large enough (rc ≳ 100 au), and only during the early phases of the disk evolution (t ≲ 1 Myr). Otherwise the dust back-reaction fails to perturb the gas motion.

Modeling Radar Albedos of Laboratory‐Characterized Particles: Application to the Lunar Surface

AbstractWe analyze lunar images obtained by the Mini Radio Frequency instrument onboard the Lunar Reconnaissance Orbiter to interpret the anomalous radar scattering observed in some lunar craters. We compare the radar signatures of the crater floors to those of the regions external to the crater rim and show that there is a systematic difference between the radar albedo trends of the two regions. Using numerical simulations to compute radar scattering properties of rock and ice particles, we demonstrate that the difference is caused partly by the near‐surface bulk volume density or the underlying fine‐grained regolith and partly by the shape and size distributions of centimeter‐to‐decimeter‐scale rubble. We show that while the size distribution of wavelength‐scale particles plays the major role in the observed radar albedos, if the size distribution is fixed, the particle shapes can play a greater role than the composition; therefore, the icy material is indistinguishable from silicate‐rich material unless the abundance of ice in the particles plays a major role in the shape of the particles.

Investigation of H atom and free radical behaviour in clathrate hydrates of organic molecules

Clathrate hydrates are icy materials composed of a lattice of water molecules containing well-defined cavities which can accommodate small guest molecules. Their large storage capacity makes clathrates attractive media for a variety of gas storage and separation applications, but there is relatively little information on the chemical stability and diffusion of guest molecules. At the fundamental level inter-cage transition energies have been calculated, but the results need to be tested with experimental data. Ideally this should involve single-atom transport, using an isotopic tracer or spin label. Muonium (Mu = μ+e–) qualifies on both counts. As a single-electron atom with the muon as nucleus it may be considered a light isotope of hydrogen. Furthermore muonium and its reaction products may be monitored by muon spin spectroscopy. In recent years we have used this method to probe H-atom and free radical behaviour in clathrate hydrates. The current work extends studies to benzene and acetone clathrate hydrates. Of note is the simultaneous detection of muonium and muoniated radicals in the same sample. This can happen when Mu is trapped in an empty cavity, remote from its reaction partner. Increase in temperature leads to transport of Mu between cages and results in encounters with reactive guest molecules. By studying the temperature dependence of Mu and radical signals, we have been able to determine the activation energy for transport of Mu between cavities.

Water delivery by pebble accretion to rocky planets in habitable zones in evolving disks

Context.The ocean mass of the Earth is only 2.3 × 10−4of the whole planet mass. Even including water in the interior, the water fraction would be at most 10−3−10−2. Ancient Mars may have had a similar or slightly smaller water fraction. What controlled the amount of water in these planets has not been clear, although several models have been proposed. It is important to clarify the control mechanism to discuss water delivery to rocky planets in habitable zones in exoplanetary systems, as well as that to Earth and Mars in our solar system.Aims.We consider water delivery to planets by icy pebbles after the snowline inwardly passes planetary orbits. We derive the water mass fraction (fwater) of the final planet as a function of disk parameters and discuss the parameters that reproduce a small value offwatercomparable to that inferred for the Earth and ancient Mars.Methods.We calculated the growth of icy dust grains to pebbles and the pebble radial drift with a 1D model, by simultaneously solving the snowline migration and dissipation of a gas disk. With the obtained pebble mass flux, we calculated accretion of icy pebbles onto planets after the snowline passage to evaluatefwaterof the planets.Results.We find thatfwateris regulated by the total mass (Mres) of icy dust materials preserved in the outer disk regions at the timing (t=tsnow) of the snowline passage of the planetary orbit. BecauseMresdecays rapidly after the pebble formation front reaches the disk outer edge (att=tpff),fwateris sensitive to the ratiotsnow∕tpff, which is determined by the disk parameters. We findtsnow∕tpff< 10 or > 10 is important. By evaluatingMresanalytically, we derive an analytical formula offwaterthat reproduces the numerical results.Conclusions.Using the analytical formula, we find thatfwaterof a rocky planet near 1 au is similar to the Earth, i.e., ~10−4−10−2, in disks with an initial disk size of 30–50 au and an initial disk mass accretion rate of ~(10−8−10−7)M⊙yr−1for disk depletion timescale of approximately a few M yr. Because these disks may be median or slightly compact/massive disks, our results suggest that the water fraction of rocky planets in habitable zones may often be similar to that of the Earth if icy pebble accretion is responsible for water delivery.

Intriguing electric field effect on magnetic spin couplings in dielectron clathrate hydrates

AbstractClathrate hydrates have appeared as promising icy materials as the radical, high‐spin molecule, and even electron clathrate hydrates are found. In particular, dielectron clathrate hydrates are expected to develop as structural units for a novel class of icy magnetic materials because of not only possible spin coupling interaction, but also very sensitive response to electric field of the loosely bound electrons. However, electric field responses concerning the magnetic properties of such hydrates have not been reported so far. In this work, three representative dielectron clathrate hydrate model clusters (e2@4668BB, e2@51262BB, and e2@4668AB) were considered for the exploration of their magnetic spin coupling properties, electron distributions, and energy responses to applied electric field. The results calculated at the density functional theory level show that the energies and electron spin coupling properties of these dielectron clathrate hydrate clusters are quite sensitive to applied electric field, presenting intriguing variations. Most importantly, applied electric field can regulate the strength of spin coupling between two trapped electrons, and even could realize the magnetic interconversion of such dielectron cluster structures between antiferromagnetic and paramagnetic or diamagnetic characteristics. Clearly, the intriguing variations should be attributed to the diffuse character, special mobility and polarizable properties of such trapped electrons, and especially the susceptible redistributions of two electrons (including the electron cloud shape and distance between two electron centers) to the electric field. This work opens up the possibility of designing novel icy magnetic materials with sensitive electric field responses of the magnetic properties.

Cryovolcanic rates on Ceres revealed by topography

Cryovolcanism, defined here as the extrusion of icy material from depth, may be an important planetary phenomenon in shaping the surfaces of many worlds in the outer Solar System and revealing their thermal histories. However, the physics, chemistry and ubiquity of this geologic process remain poorly understood, especially in comparison to the better-studied silicate volcanism on the terrestrial planets. Ceres is the only plausibly cryovolcanic world to be orbited by a spacecraft up to now, making it the best opportunity to test the importance of cryovolcanism on bodies in the outer Solar System and compare its effects to silicate volcanism on terrestrial planets. Here, we analyse images from NASA’s Dawn mission and use the finite element method to show that Ceres has experienced cryovolcanism throughout its geologic history, with an average cryomagma extrusion rate of ~10^4 m^3 yr^(−1). This result shows that volcanic phenomena are important on Ceres, but orders of magnitude less so than on the terrestrial planets.