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Efficiently and accurately calculating the plasma transport process is one of the difficulties in aerospace plasma application simulation, especially in the magnetic sail spacecraft applications that have a huge size. This paper develops a three-dimensional trilinear anisotropic immersed-finite-element direct-implicit particle-in-cell (IFE-DIPIC) model to solve the problem of large-scale, long-term evolution plasma with complex interfaces. The model uses the DIPIC method to track the motion of particles in the plasma while simulating the anisotropic electric field containing an interface by using a modified trilinear anisotropic IFE method. Compared to the previous models, the developed model in this paper allows for the use of larger spatial and time steps in the Cartesian meshes without inducing numerical divergence. Using an interface-independent mesh avoids redundant interpolation in the PIC method, further improving efficiency. These advantages significantly improve the efficiency in solving actual complex three-dimensional plasma physics problems. The accuracy, efficiency, stability, and applicability of the proposed model are proved through numerical examples and the application in magnetic sail. The simulation results indicate that the developed model can efficiently simulate the actual working conditions of magnetic sails. The performance is significantly influenced by both the direction and magnitude of the magnetic moment. [ABSTRACT FROM AUTHOR]

Observations of Uranus in the near‐infrared by ground‐based telescopes from 1992 to 2018 have shown that the planet's upper atmosphere (thermosphere) steadily cooled from ∼700 to ∼450 K. We explain this cooling as due to the concurrent decline in the power of the solar wind incident on Uranus' magnetic field, which has dropped by ∼50% over the same period due to solar activity trends longer than the 11‐year solar cycle. Uranus' thermosphere appears to be more strongly governed by the solar wind than any other planet where we have assessed this coupling so far. Uranus' total auroral power may also have declined, in contrast with the power of the radio aurora that we expect has been predominantly modulated by the solar cycle. In the absence of strong local driving, planets with sufficiently large magnetospheres may also have thermospheres predominantly governed by the stellar wind, rather than stellar radiation. Plain Language Summary: So far, we have only explored the Uranus planetary system with the Voyager 2 spacecraft, which flew past in 1986. This encounter led to many discoveries, and as many mysteries. One of these mysteries has only become clear since the flyby, as ground‐based telescopes have been monitoring the temperature of Uranus' tenuous upper atmosphere and have found that this layer has been getting colder and colder since the Voyager era, unlike the deeper atmosphere that has stayed about the same temperature. By 2018 the temperature of this upper layer had almost halved, and neither the 11‐year cycle of solar activity nor Uranus' changing seasons appear to have been in control. We finally provide a solution to this long‐standing problem by identifying that the energy input to Uranus' magnetic field by the tenuous, high‐speed flow of charged particles from the Sun has been similarly declining over decades. This interaction is what drives energy flow through space around the planet, and this energy ultimately does most of the heating of the upper atmosphere, where auroras are generated. We highlight that the situation may be similar at exoplanets with similarly large magnetospheres. Key Points: Ground‐based telescopes have shown that Uranus' thermosphere steadily and dramatically cooled from ∼1992 to ∼2018We explain this cooling as due to declining solar wind kinetic power incident on Uranus' magnetosphere controlling thermosphere temperatureUranus' thermosphere appears to be governed by the solar wind, total auroral power may have also declined over the same period [ABSTRACT FROM AUTHOR]

The solar wind interaction with planetary magnetospheres dictates the mechanism through which energy is transported across planetary systems. The magnetohydrodynamic plasma description suggests that solar wind conditions in the outer solar system encourage the magnetopause boundaries at Uranus and Neptune to be more Kelvin‐Helmholtz unstable, however, no quantitative assessment has been performed. To characterize the viscous solar wind interaction at Uranus and Neptune, we create an analytical model to determine where Kelvin‐Helmholtz Instabilities (KHIs) may form along their magnetopauses by searching for regions where the minimum condition for KHI formation is satisfied. We run the model at solstice and equinox for a range of Interplanetary Magnetic Field (IMF) strengths, and rotation phases. We find minimal seasonal variation for low IMF strengths (B = 0.01 nT), with ∼70% of the magnetopause surface at Uranus and ∼80% at Neptune, enabling KHI formation. For periods of stronger IMF strength (B > 0.3 nT), KHIs were significantly suppressed. While KHIs depend on both the conditions inside the magnetopause boundary and the shocked solar wind IMF strength, we find that the IMF strength is the most significant criterion in determining whether or not KHIs are allowed to form at the magnetopause boundaries. Plain Language Summary: As the solar wind travels through the solar system, it interacts with planetary magnetic fields. Understanding how the solar wind interacts with the magnetic fields is important because it dictates how mass, momentum and energy are transported through the planetary system. In the outer solar system, it is thought that vortex‐like structures called Kelvin‐Helmholtz Instabilities (KHIs) will form at the boundary where the solar wind reaches the planetary magnetic field. We present the results of an analytical model that determines where KHIs may form along this boundary. We find that, for both Uranus and Neptune, the KHIs are most likely to develop if the interplanetary magnetic field is small, at all rotation orientations, and at both their solstice and equinox magnetospheric configurations. Key Points: Kelvin‐Helmholtz Instabilities can form at the magnetopause at Uranus and Neptune at both solstice and equinoxKelvin‐Helmholtz Instabilities are more likely to develop in environments where the interplanetary magnetic field strength is smallBoth Uranus and Neptune see minimal variation in the regions where Kelvin‐Helmholtz Instabilities can form over a planetary rotation [ABSTRACT FROM AUTHOR]

Magnetic flux ropes are ubiquitous in various space environments, including the solar corona, interplanetary solar wind, and planetary magnetospheres. When these flux ropes intertwine, magnetic reconnection may occur at the interface, forming disentangled new ropes. Some of these newly formed ropes contain reversed helicity along their axes, diverging from the traditional flux rope model. We introduce new observations and interpretations of these newly formed flux ropes from existing Hall Magnetohydrodynamics model results. We first examine the time‐varying local magnetic field direction at the impact interface to assess the likelihood of reconnection. Then we investigate the electric current system to describe the evolution of these structures, which potentially accelerate particles and heat the plasma. This study offers novel insights into the dynamics of space plasmas and suggests a potential solar wind heating source, calling for further synthetic observations. Plain Language Summary: This research examines a special type of systematically twisted magnetic fields, known as flux ropes, in the sun's atmosphere, the solar wind, and near planets. Built on earlier model results, this examination brings a new understanding of how these special flux ropes emerge from collisions between flux ropes. These results use a commonly used simulation tool for large‐scale plasmas to study the new ropes formed after two flux ropes are pushed toward each other long enough. In some cases, each of the new ropes may have opposite twists between their two ends. We then examine how the magnetic field changes across the interface during the evolution. Changes in electric currents found in these situations further explain the formation and evolution of the new rope pairs. This examination helps to better understand the behavior of space plasma's heating of the solar wind and its control of space weather. Key Points: We examine the interaction of magnetic flux ropes that consist of opposite helicity along their axes using numerical simulationsWe present the evolution of their current system, from which we anticipate a significant amount of energy releaseThese structures could be present on the solar surface, in the solar wind, and in magnetospheres [ABSTRACT FROM AUTHOR]

The magnetotail lobe region at Mercury is characterized by low plasma density and low magnetic field variability compared to the nightside magnetosheath and central plasma sheet. At Mercury, as well as other planets, lobe magnetic fields play a crucial role in storing and releasing magnetic flux in response to changing upstream solar wind conditions such as interplanetary magnetic field (IMF) orientation and solar wind dynamic pressure (Pdyn). This makes the region significant for studying the magnetospheric interaction with the intense solar wind conditions at Mercury's orbit. Here, we identify and analyze magnetotail lobe observations made by the Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft during its 4 years orbital phase. We empirically determined a set of criteria using magnetometer (MAG) and the Fast Imaging Plasma Spectrometer instruments onboard MESSENGER to identify lobe magnetic field intervals. From 3,332 MESSENGER orbits, we identify 1,242 lobe field intervals. We derive an expression for the average lobe magnetic field strength in nanotesla with respect to radial distance downtail: Blobe(r) = (135 ± 8) * r(−2.1±0.3) + (31 ± 8). The lobe magnetic field exhibits both small‐scale (∼3 min) and orbit‐to‐orbit (∼8–12 hr) variability in magnetic field strength compared to this averaged field strength expression. The orbit‐to‐orbit variability in lobe field strength is not significantly correlated with estimated IMF orientation, but is directly correlated with Pdyn. Thus, our findings provide evidence for the pressure balance between the inward facing Pdyn on the nightside magnetopause and the outward facing magnetic pressure supplied by the lobes. Plain Language Summary: Of all the planets in the Solar System, Mercury orbits closest to the Sun. As a result, it is subjected to an extreme interplanetary environment driven by solar dynamics. One consequence of the electro‐magnetic interaction of the Sun and Mercury is the formation of the magnetotail, which is the result of magnetic field lines connected to the planet being dragged toward the nightside. A portion of the magnetotail, known as the lobe, is characterized by a relative lack of plasma density compared to the surrounding environment. The strength of the magnetic field in the lobe is directly correlated with the conditions in the interplanetary space surrounding Mercury, making it an important region to study the response of a planetary environment to the extreme conditions at Mercury's orbit. We identify and analyze times in which the Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft observed this important region of Mercury's plasma environment. We find direct evidence for the magnetic field lobe's response to the plasma properties emanating from the Sun. Key Points: 1,242 intervals in which Mercury Surface, Space Environment, Geochemistry and Ranging observed the southern lobe of Mercury were identified in 4 years of orbital dataThe lobe field strength (in nT) falls off with distance downtail according to Blobe(r) = (135 ± 8) * r(−2.1±0.3) + (31 ± 8)Orbit‐to‐orbit variability in lobe field strength is directly attributable to changing upstream solar wind dynamic pressure [ABSTRACT FROM AUTHOR]

Discrete aurora at Mars are characterized as localized, short‐lasting ultraviolet emissions on the nightside. They are caused by the precipitation of accelerated electron along open magnetic field lines and their collision with the Martian atmosphere. Discrete auroral emissions detected by the Imaging Ultraviolet Spectrograph (IUVS) instrument onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft occur most frequently over the strongest crustal magnetic anomalies at Mars and under particular local time and upstream interplanetary magnetic field (IMF) conditions. These trends suggest that the onset of discrete aurora is controlled by the processes that govern the interaction between the draped IMF and the crustal magnetic anomalies. Here, we analyze MAVEN magnetometer measurements over regions of strong crustal fields during 49 discrete auroral events observed by IUVS. Our results indicate that the draped IMF orientations during each discrete auroral event show a clear tendency to be anti‐parallel to the underlying crustal anomaly magnetic fields near the location of the emission onset. This suggests that magnetic reconnection, a process that favors anti‐parallel magnetic field regimes, between the crustal fields and the draped IMF plays a role in discrete aurora formation. Of the 49 discrete auroral events analyzed, 42 (86%) occurred under draped IMF conditions that are susceptible to reconnection with the underlying crustal anomalies. This investigation produces strong evidence linking discrete aurora to magnetic reconnection at Mars and provides insights into other trends in discrete auroral activation such as local time and upstream IMF conditions. Plain Language Summary: There are regions on the surface of Mars that possess strong magnetic fields. Ultraviolet aurora known as "discrete aurora" at Mars are observed most frequently over a region of these strong crustal fields and are caused by the energetic collision between charged particles and the Martian atmosphere. These particles are thought to be the result of the interaction between Martian magnetic fields and the flow of charged particles and interplanetary magnetic field (IMF) known as the solar wind. Our work analyzes magnetic field observations from the magnetometer onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft along orbits in which discrete aurora were detected over a region of strong crustal magnetism. We find that discrete auroral emissions over these strong crustal magnetic fields occur most frequently when the surrounding draped IMF conditions are susceptible to undergoing a process called "magnetic reconnection," in which magnetic field lines are reassigned into a different magnetic connectivity. This is the first study to definitively link the process of discrete aurora to magnetic reconnection and provides a framework for understanding previously unexplained trends in discrete aurora activation at Mars. Key Points: Discrete aurora over two regions of crustal fields at Mars occur under specific draped magnetic field conditionsOf the 49 discrete aurora analyzed, 42 (86%) occur under conditions that favor anti‐parallel magnetic reconnectionReconnection plays a role in discrete aurora onset, explaining trends in auroral detections including local time and upstream conditions [ABSTRACT FROM AUTHOR]

We discuss possible existence of a magnetodisk around the exoplanet HAT–P–11b. We used available observations to determine properties of the exoplanet and the stellar wind passing by it and obtained a rough estimate of the size of the planet's magnetosphere. Comparing our estimate to published results of computations in a 3D electromagnetic relativistic and collisionless particle-in-cell model of the magnetosphere, we found a discrepancy in the magnetosphere size estimated using these two techniques. A possible interpretation of the discrepancy is suggested. [ABSTRACT FROM AUTHOR]

In Trung et al. (2019b, https://doi.org/10.1029/2019ja026636), we compared the geopause, a surface where the ionospheric plasma and solar wind plasma has equal parameters (by mass density, number density, or pressure), to the magnetopause to show that there was a transition in physics governing the motion of the plasmas between the different boundaries. In this study, we use multifluid magnetohydrodynamics simulation data to examine the relation of the source terms in the momentum equation and to the geopauses. We find that the geopauses do represent a transition in the physics governing the motion of the plasmas. While friction does not play a dominant role in the motion of the heliospheric and ionospheric plasmas, we find that friction shows indirectly that the ionospheric plasma can travel faster than the heliospheric plasma. Further satellite data is needed to verify the possibility of ionospheric plasma reaching speeds exceeding the solar wind. Key Points: We used numerical simulations to compare the structure of source terms in the multifluid momentum equation to the geopauseGeopauses represent a transition in how source terms govern the motion of individual plasma componentsFriction shows that ionospheric plasma can travel faster than the solar wind [ABSTRACT FROM AUTHOR]

In April 2023, the Jupiter Icy Moons Explorer (Juice) began its journey to orbit Jupiter's largest and only magnetic moon, Ganymede. Part of the mission's objectives aim to verify existence of the moon's subsurface ocean and determine its structure through its induced response to external excitation by periodically varying magnetic field. Known contributions to the excitation are those from Jupiter's dipole (at synodic period) and quadrupole (at half-synodic period) variations, and Ganymede's inclined eccentric orbit around Jupiter (at orbital period). We propose that Ganymede's magnetopause, where the Chapman–Ferraro (C–F) magnetic field arises from local currents, also contributes to subsurface ocean induction. This article introduces the first three-dimensional model of the C–F field and its outputs at Ganymede's subsurface ocean and larger magnetosphere. The field is shown to be non-uniform — strongest near upstream Ganymede's subflow region and gradually weakening away from it. Magnetopause asymmetry due to the Jovian guide field results in largely synodic variation of the C–F field, with exceptions near Ganymede's equator and subflow meridian where asymmetry effects are minimal and the variations are half-synodic. The C–F field amplitude is of general order ∼ 50 nT, which is significant relative to excitation from the Jovian field. Comparisons to Galileo data and magnetohydrodynamic simulation results suggest the model is useful, therefore the magnetopause effects must be considered in future induction modeling of Ganymede's subsurface ocean ahead of the Juice mission. • We present a new 3D analytical model of Chapman–Ferraro magnetic field for Ganymede. • The C–F field of ∼ 50 nT varies synodically (10.5 h) at Ganymede's subsurface ocean. • The C–F field therefore must be included in ocean studies through magnetic induction. [ABSTRACT FROM AUTHOR]

While there have been far fewer missions to the outer Solar System than to the inner Solar System, spacecraft destined for the giant planets have conducted a wide range of fundamental investigations, returning data that continues to reshape our understanding of these complex systems, sometimes decades after the data were acquired. These data are preserved and accessible from national and international planetary science archives. For all NASA planetary missions and instruments the data are available from the science discipline nodes of the NASA Planetary Data System (PDS). Looking ahead, the PDS will be the primary repository for giant planets data from several upcoming missions and derived datasets, as well as supporting research conducted to aid in the interpretation of the remotely sensed giant planets data already archived in the PDS. [ABSTRACT FROM AUTHOR]

Life on earth is protected from astrophysical cosmic rays by the heliospheric magnetic and slowly varying geomagnetic fields, and by collisions with oxygen and nitrogen molecules in the atmosphere. The collisions generate showers of particles of lesser energy; only muons, a charged particle with a mass between that of an electron and a proton, can reach earth’s surface in substantial quantities. Muons are easily detected, used to image interior spaces of pyramids, and known to limit the stability of qubits in quantum computing; yet, despite their charge, average energy of 4 GeV and ionizing properties, muons are not considered to affect chemical reactions or biology. In this Perspective the potential damaging effects of muons on DNA, and hence the repercussions for evolution and disease, are examined. It is argued here that the effect of muons on life through DNA mutations should be considered when investigating the protection provided by the magnetic environment and atmosphere from cosmic rays on earth and exoplanets.

The Jovian system is very intriguing with extremely different particle sources. As the dominant source of particles to Jupiter's magnetosphere, Io is of particular importance. The JAXA Hisaki (SPRINT‐A) mission is providing insightful observations with regard to Io. In particular, its UV neutral oxygen line of sight observations provide the best glimpse so far of Jovian neutral particle populations. This is exciting in that for the first time, the neutral tori can be directly observed on time scales that constrain satellite sources. This data also sheds unprecedented insight into neutral torus distributions, which could subsequently provide essential information about the sources and mechanisms from Io. However, 3‐D modeling is also required to interpret the complex and dynamic observational geometries. Here, we present the first 3‐D distribution of the Io‐generated neutral oxygen torus using JAXA Hisaki neutral oxygen observations as modeling constraints to provide characterization of the Io magnetospheric source and the resulting neutral tori. Major findings of our research include: (a) the effective total original SO2 source rate from Io during a low activity period is ∼800 kg/s; (b) Io has two separate exospheric sources: O at ∼200 kg/s and SO2 at ∼400 kg/s; (c) particles escape from Io preferentially on the Jupiter upstream facing hemisphere; (d) the oxygen neutral torus populates the entire orbit and significantly dominates over the SO2, SO, and S neutral toroidal clouds; and (e) large ionization and dissociation rates limit the significant expansion of Io‐genic neutral particles in Jupiter's magnetosphere beyond ∼2 Rj from Io's orbit. Plain Language Summary: The Jovian system is very intriguing with extremely different particle sources. As the dominant source of particles to Jupiter's magnetosphere, Io is of particular importance. The JAXA Hisaki (SPRINT‐A) mission is providing insightful observations with regard to Io. This is exciting in that for the first time, the extended neutral particle distribution can be directly observed on time scales that constrain satellite sources. This data also sheds unprecedented insight into neutral particle distributions in Jupiter's magnetosphere, which could subsequently provide essential information about the sources and mechanisms from Io. However, 3‐D modeling is also required to interpret the complex and dynamic observational geometries. Here, we present the first 3‐D distribution of the Io‐generated neutral oxygen torus using JAXA Hisaki neutral oxygen observations as modeling constraints to provide characterization of the Io magnetospheric source and the resulting neutral tori. Major findings of our research include: Io has two separate exospheric sources: O at ∼200 kg/s and SO2 at ∼400 kg/s; particles escape from Io preferentially on the Jupiter upstream facing hemisphere; the oxygen neutral torus populates the entire orbit and significantly dominates over the SO2, SO, and S; and neutral particles from Io remain close to its orbit. Key Points: The first 3‐D distribution of the Io‐generated neutral oxygen torus using JAXA Hisaki neutral oxygen observations as modeling constraintsIo has two separate exospheric sources (preferentially escaping on the Jupiter facing hemisphere): O at ∼200 kg/s and SO2 at ∼400 kg/sThe oxygen neutral torus populates the entire orbit and significantly dominates over the SO2, SO, and S neutral toroidal clouds [ABSTRACT FROM AUTHOR]

Because of finite-gyroradii effects, the atmospheric loss cone for energetic particles in the magnetosphere is shifted away from the magnetic-field direction. Using the Tsyganenko T96 magnetic-field model, maps of the magnitude of the angular shift of the loss cone are created for electrons, protons, and singly-ionized oxygen in the nightside magnetosphere. When the shift exceeds about 5°–10°, stochastic scattering of particles occurs. For protons and oxygen, this loss-cone shift is quite large, even in the dipolar portions of the magnetosphere, and stochastic scattering of protons and oxygen can occur in those regions. Hence, the ring-current ion population probably exhibits a robustly shifted loss cone and stochastic scattering in the dipole magnetosphere. For electrons, large loss-cone shifts and stochastic scattering are restricted to the magnetotail near and beyond the transition region.

Ultra-Low-Frequency (ULF) waves provide a means for the rapid propagation of energy and field-aligned current in planetary magnetospheres. At Earth, the ULF frequency range is usually defined as including waves with periods of 0.2–600 s; however, at Jupiter these waves can extend to periods of tens of minutes. In both magnetospheres, shear mode Alfvén waves can form field line resonances that exist between the ionospheres, with periods of a few minutes at Earth and a few tens of minutes at Jupiter. A major distinction between these two magnetospheres is in the density distribution. Earth has a dense ionosphere full of heavy ions, an extended, cold plasmasphere and a relatively low-density plasma sheet. In contrast, at Jupiter, the ionosphere is largely hydrogen (both in atomic form and in the H3+ molecular ion), there is no appreciable plasmasphere and the plasma disk is dense and populated with heavy ions (largely sulfur and oxygen) originating at the moon Io and to some extent from other moons. As at Earth, the sharp Alfvén speed gradient above the ionosphere forms an ionospheric Alfvén resonator at Jupiter with periods of seconds. Furthermore, the high-latitude lobes at Jupiter have very low density and a resonant structure can be formed by waves bouncing between the ionosphere and the dense plasma disk. This structure leads to periods of tens of seconds. Finally, the dense Io plasma torus and plasma sheet provide conditions for compressional cavity modes to form in this region. Thus, the structure of the field line resonance modes is quite different at the two planets. Implications of these resonances on auroral particle acceleration will be discussed.

Sodium and potassium signatures in transiting exoplanets can be challenging to isolate from the stellar absorption lines. Here, these challenges are discussed in the framework of Solar System observations, and transits of Mercury in particular. Radiation pressure is important for alkali gas dynamics in close-orbiting exoplanets since the D lines are efficient at resonant scattering. When the star-planet velocity is ≳10 km/s, eccentric exoplanets experience more than an order of magnitude higher radiation pressures, aiding atmospheric escape and producing a larger effective cross-section for absorbing starlight at the phase of transit. The Doppler shift also aids in isolating the planetary signature from the stellar photosphere’s absorption. Only one transiting exoplanet, HD 80606b, is presently thought to have both this requisite Doppler shift and alkali absorption. Radiation pressure on a planetary exosphere naturally produces blue-shifted absorption, but at levels insufficient to account for the extreme Doppler shifts that have been inferred from potassium transit measurements of this system. In the absence of clear mechanisms to generate such a strong wind, it is described how this characteristic could arise from an exomoon-magnetosphere interaction, analogous to Io-Jupiter. At low contrasts presented here, follow-up transit spectra of HD 80606b cannot rule out a potassium jet or atmospheric species with a broad absorption structure. However, it is evident that line absorption within the imaging passbands fails to explain the narrow-band photometry that has been reported in-transit. New observations of energetic alkalis produced by the Io-Jupiter interaction are also presented, which illustrate that energetic sodium Doppler structure offers a more valuable marker for the presence of an exomoon than potassium.

In the Earth’s dipole magnetosphere finite-gyroradius effects produce a shift of the atmospheric loss cone away from the direction of the magnetic field. This loss-cone shift is theoretically described by the “Mozer transform” [Mozer, F. S. (1966). Proton trajectories in the radiation belt. J. Geophys. Res. 71:2701], which is based upon the curvature drift of particles crossing the equatorial plane. For positive ions the northern and southern loss cones both shift westward and for electrons the northern and southern loss cones both shift eastward. This loss-cone shift is part of a coordinate-system transform, with the transformed coordinates better organizing the behavior of particle orbits in the dipole magnetic field (e.g. first adiabatic invariants, mirror heights, and bounce times). In this report it is demonstrated that the transformed coordinate system also properly organizes pitch-angle diffusion. This improved organization of the diffusion is true whether the angular scattering is produced by plasma-wave scattering or by field-line-curvature (FLC) scattering. It is shown that FLC scattering and the loss cone shift are linked, so that if FLC scattering is occurring, there is a loss cone shifted away from the magnetic-field direction and the Mozer-transformed coordinates are needed.

The temperatures of ions in the magnetospheres of Jupiter and Saturn were observed to increase substantially from about 10 to 30 planet radii. Different heating mechanisms have been proposed to explain such observations, including a heating model for Jupiter based on magnetohydrodynamic (MHD) turbulence with flux‐tube diffusion. More recently, an MHD turbulent heating model based on advection was shown to also explain the temperature increase at Jupiter and Saturn. We further develop this turbulent heating model by combining effects from both diffusion and advection. The combined model resolves the physical consistency requirement that diffusion should dominate over advection when the radial flow velocity is small and vice versa when it is large. Comparisons with observations show that previous agreements, using the advection only model, are still valid for larger radial distance. Moreover, the additional heating by diffusion results in a better agreement with the temperature observations for smaller radial distance. Plain Language Summary: The temperatures of ions in the magnetospheres of Jupiter and Saturn were observed to increase substantially near the planet. This suggests that there should be some heating sources to counter the cooling effect due to expansion. There have been several models trying to explain such observation using different heating mechanisms, including a heating model for Jupiter based on turbulence and diffusion effects, as well as a model based on advection effects for Jupiter and Saturn. We further develop a heating model by combining effects from both diffusion and advection. The combined model resolves the physical consistency requirement that diffusion should be stronger than advection nearer to the planet, but shifting to the opposite farther away. Comparisons with observations show that previous agreements using the advection only model are still valid, and are improved by including diffusion nearer to the planet. Key Points: A new model for the heating of the magnetospheres of Jupiter and Saturn by magnetohydrodynamic turbulence is developedThe model combines effects from diffusion and advection such that each is dominant when the radial velocity is small or large, respectivelyPredictions of the temperature and radial velocity profiles agree better with Jupiter and Saturn observations than previous models [ABSTRACT FROM AUTHOR]

The parameters of pulsars with detected giant pulses (GPs) and the known models proposed to describe the GP phenomenon have been analyzed. The angles between the magnetic moment and the rotation axis of the neutron star have been estimated for such pulsars. This parameter is important in a number of analyzed models. It is noted that there is likely no unified model to explain all the features of GPs. Kontorovich's model and the model by Machabeli et al. appear to be the most promising for describing GPs. In the first model, GPs are formed in a vacuum gap near the surface of a neutron star. The existence of such a gap and the presence of electric fields in it is considered generally accepted today. The second model explains GPs through nonlinear processes in plasma during the generation of drift waves at the periphery of the pulsar's magnetosphere. The appearance of such waves, apparently, can also be considered inevitable, and their role in the observed phenomena can be significant. A more detailed development of each of the models is necessary to draw more definite conclusions about their role in the formation of GPs. This problem seems all the more relevant in light of the possibility of using the GP phenomenon to explain fast radio bursts. [ABSTRACT FROM AUTHOR]

This paper investigates jovian current disk properties utilizing two complementary Juno JADE-I data sets. We set out to extract plasma parameters for multiple ion species: H + , S + , S + + + , O + + and O + or S + +. The JADE-I Time-of-Flight (TOF) sensor has little directional information yet can separate out ion species by mass per charge, however O + and S + + have the same mass to charge so are represented by a single average ion of equivalent mass per charge. The JADE-I SPECIES data set has coarse mass per charge information yet is directional. By utilizing both data sets we can extract densities, velocities and temperatures using forward model techniques and assuming a Maxwellian distribution. However, it became apparent that the proton distributions were inadequately represented by a single Maxwellian distribution, being far too broad in energy and/or having multiple distributions, such that numerical moments were used to derive proton properties. The forward model technique was used on the remaining heavy ions, with a singular distribution for each ion species but a shared velocity. Both Maxwellian and Kappa distributions were investigated to see how well they represented the data. While a high energy tail can be readily observed in the TOF data set, the signal was low, and it was difficult to identify the same tail in the SPECIES data set. After investigation, it was found that assuming Kappa distributions had little benefit over assuming Maxwellian distributions, therefore the main forward model analysis was carried out assuming 4 co-moving Maxwellian distributed heavy ion species. The main study was for Juno orbits 5 to 34, where the trajectories had full current disk crossings outside of 20 jovian radii. Comparing the velocities of the heavy ion fits to the protons numerical moments gave good agreement, endorsing both analysis techniques. Radial profiles of plasma parameters of the current disk are provided, that highlight how the O + and S + + ions are the dominant ion species with relative ion composition fixed over these radial distances. If the heavy ions were to be treated as an average single ion species, they would have a mass to charge of 15.1 amu/q for the radial range 23–63 jovian radii. • Protons are poorly represented by a single Maxwellian or Kappa distribution. • JADE Time-of-Flight & SPECIES are simultaneously fit to extract heavy ion properties. • Moments of an average ion underestimated parameters compared to fits of 4 ion species. • An average m / q of 25.3/1.7 = 15.1 amu/q for the heavy ions was found for 23-63 R J. [ABSTRACT FROM AUTHOR]

Uranus and Neptune possess highly tilted/offset magnetic fields whose interaction with the solar wind shapes unique twin asymmetric, highly dynamical, magnetospheres. These radiate complex auroral emissions, both reminiscent of those observed at the other planets and unique to the ice giants, which have been detected at radio and ultraviolet (UV) wavelengths to date. Our current knowledge of these radiations, which probe fundamental planetary properties (magnetic field, rotation period, magnetospheric processes, etc.), still mostly relies on Voyager 2 radio, UV and in situ measurements, when the spacecraft flew by each planet in the 1980s. These pioneering observations were, however, limited in time and sampled specific solar wind/magnetosphere configurations, which significantly vary at various timescales down to a fraction of a planetary rotation. Since then, despite repeated Earth-based observations at similar and other wavelengths, only the Uranian UV aurorae have been re-observed at scarce occasions by the Hubble Space Telescope. These observations revealed auroral features radically different from those seen by Voyager 2, diagnosing yet another solar wind/magnetosphere configuration. Perspectives for the in-depth study of the Uranian and Neptunian auroral processes, with implications for exoplanets, include follow-up remote Earth-based observations and future orbital exploration of one or both ice giant planetary systems. [ABSTRACT FROM AUTHOR]

We use a global magnetohydrodynamic (MHD) model to simulate Mercury's space environment for several solar wind and interplanetary magnetic field (IMF) conditions in anticipation of the magnetic field measurements by the MESSENGER spacecraft. The main goal of our study is to assess what characteristics of the internally generated field of Mercury can be inferred from the MESSENGER observations, and to what extent they will be able to constrain various models of Mercury's magnetic field generation. Based on the results of our simulations, we argue that it should be possible to infer not only the dipole component, but also the quadrupole and possibly even higher harmonics of the Mercury's planetary magnetic field. We furthermore expect that some of the crucial measurements for specifying the Hermean internal field will be acquired during the initial fly-bys of the planet, before MESSENGER goes into orbit around Mercury. © 2008 Elsevier Inc. All rights reserved.

Planned active space experiments and ideas for future active space experiments are reviewed. Three active experiments being readied are DSX (Demonstration and Space eXperiments), SMART (Space Measurement of Rocket-released Turbulence), and BeamPIE (Beam Plasma Interaction Experiment). Ideas for future experiments include relativistic-electron-beam experiments for magnetic-field-line tracing, relativistic-electron-beam experiments to probe the middle atmosphere, plasma-wave launching using superparamagnetic-nanoparticle amplification of magnetic fields, the heavy-ion mass loading of collisionless magnetic-field-line reconnection, the use of electrostatically charged tethers to pitch-angle scatter radiation-belt particles, cold plasma releases to modify magnetospheric plasma physics, and neutral-gas releases to enhance neutral-particle imaging of the magnetosphere. Technologies that are being developed to enable future space active experiments are reviewed: this includes the development of compact relativistic accelerators, superparamagnetic particle amplified antennae, CubeSats, and a new understanding of how to control dynamic spacecraft charging. New capabilities to use laboratory facilities to design space active experiments as well as new computer-simulation capabilities to design and understand space active experiments are reviewed.

Langmuir probes have been widely used for in situ measurements of ambient plasma in space. However, in situations where the Debye sheath is relatively large (e.g., planetary magnetospheres and solar wind plasma), probes with a limited boom length have a risk of being engulfed by the sheath of the spacecraft (SC) as indicated in previous missions, causing errors in derived plasma parameters. Here we present a double hemispherical probe (DHP) technique which is able to identify whether the probe is in the SC sheath and retrieve true plasma parameters. The DHP consists of two hemispheres that are installed back‐to‐back and electrically isolated from each other. The two hemispheres are swept with the same bias voltage simultaneously. It is shown that the currents of the two hemispheres diverge when the probe is in the sheath. Through laboratory experiments, empirical relationships are established between the current ratio of the two hemispheres, measured parameters in the sheath, and true ambient plasma parameters. Using these relationships, the plasma parameters retrieved from the DHP measurements in the sheath show good agreement with the true ambient plasma parameters. The DHP technique significantly improves the measurement accuracy across a wide range of plasma environments. Key Points: Spacecraft sheath affects the measurements of Langmuir probesThe double hemispherical Langmuir probe can retrieve accurate measurements of the plasma parameters even in the sheath [ABSTRACT FROM AUTHOR]

The boundary separating solar wind plasma from ionospheric plasma is typically thought to be the magnetopause. A generalization of the magnetopause concept called the geopause was developed by Moore and Delcourt (1995, https://doi.org/10.1029/95RG00872). The geopause is a surface defined where solar wind quantities equal the ionospheric quantities. Geopause studies have helped characterize magnetospheric systems. However, comparative studies between the geopauses to the magnetopause have not been conducted. In this paper, we analyze the influence of inner boundary composition and interplanetary magnetic field (IMF) orientation on the steady state terrestrial geopauses and the magnetopause. This study simulates the Earth's magnetosphere by using the multifluid capabilities of the Block Adaptive Tree Solar wind Roe‐type Upwind Scheme magnetohydrodynamics model within the Space Weather Modeling Framework. The simulations show that the dayside magnetopause was not influenced by the presence of oxygen in the outflow for both IMF orientations and was larger than the other geopauses. In contrast, the nightside magnetopause was sensitive to the conditions in the outflow. The nightside magnetopause was smaller than the other geopauses with southward IMF. With northward IMF, the nightside magnetopause was the largest structure in comparison with the plasma‐based geopauses. Our results indicate that no single boundary surface dictates the transition from a solar wind dominated plasma to ionosphere dominated plasma. Key Points: Four definitions of the geopause are compared: number density, mass density, plasma pressure, and last closed field line (magnetopause)Multifluid magnetohydrodynamic modeling is used to calculate these geopauses for idealized north and south interplanetary magnetic fieldThe magnetopause is farthest out during north interplanetary field, but the plasma geopauses are farthest during south field [ABSTRACT FROM AUTHOR]

Theoretical models play an important role in the Planetary Space Weather Services (PSWS) of the European Planetary Network (“Europlanet”), due to their ability to predict the physical response of magnetospheric environments to compressions or rarefactions in the upstream solar wind flow. We illustrate this aspect by presenting examples of some calculations done with the UCL Magnetodisc Model in both “Jupiter” and “Saturn” mode. Similar model outputs can now be provided via the PSWS MAGNETODISC service. For each planet’s space environment, we present example model outputs showing the effect of compressions and rarefactions on the global magnetic field, plasma pressure and azimuthal current density. As a simple illustration of the physics underlying these reference models, we quantify solar wind effects by comparing the “compressed” and “expanded” outputs to a nominal “average-state” model, reflecting more typical solar wind dynamic pressures. We also describe the implementation of the corresponding PSWS MAGNETODISC Service, through which similar outputs may be obtained by potential users.

Highlights • MAVEN has observed the Martian upper atmosphere for a full Martian year, and has determined the rate of loss of gas to space and the driving processes; 1–2 kg/s of gas are being lost. • The loss rate extrapolated back in time gives an estimate of the total loss of gas to space and its impact on Martian climate history; an estimated 0.8 bars or more of CO2 likely has been lost. • Loss to space has been the major process driving climate change on Mars. Abstract Observations of the Mars upper atmosphere made from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft have been used to determine the loss rates of gas from the upper atmosphere to space for a complete Mars year (16 Nov 2014 – 3 Oct 2016). Loss rates for H and O are sufficient to remove ∼2–3 kg/s to space. By itself, this loss would be significant over the history of the planet. In addition, loss rates would have been greater early in history due to the enhanced solar EUV and more-active Sun. Integrated loss, based on current processes whose escape rates in the past are adjusted according to expected solar evolution, would have been as much as 0.8 bar CO 2 or 23 m global equivalent layer of H 2 O; these losses are likely to be lower limits due to the nature of the extrapolation of loss rates to the earliest times. Combined with the lack of surface or subsurface reservoirs for CO 2 that could hold remnants of an early, thick atmosphere, these results suggest that loss of gas to space has been the dominant process responsible for changing the climate of Mars from an early, warmer environment to the cold, dry one that we see today. [ABSTRACT FROM AUTHOR]

Abstract: Between April and the end of its mission on 15 September, Cassini executed a series of 22 very similar 6.5‐day‐period proximal orbits, covering the mid‐latitude region of the nightside magnetosphere. These passes provided us with the opportunity to examine the variability of the nightside plasma sheet within this time scale for the first time. We use Cassini particle and magnetic field data to quantify the magnetospheric dynamics along these orbits, as reflected in the variability of certain relevant plasma parameters, including the energetic ion pressure and partial (hot) plasma beta. We use the University College London/Achilleos‐Guio‐Arridge magnetodisk model to map these quantities to the conjugate magnetospheric equator, thus providing an equivalent equatorial radial profile for these parameters. By quantifying the variation in the plasma parameters, we further identify the different states of the nightside ring current (quiescent and disturbed) in order to confirm and add to the context previously established by analogous studies based on long‐term, near‐equatorial measurements. [ABSTRACT FROM AUTHOR]

The near‐Mars space environment has a number of regions and boundaries that have numerous and confusing labels. The whole region is sometimes referred to as the induced Martian magnetosphere and sometimes as the solar wind interaction with Mars. The middle boundary where the shocked solar wind plasma gives way to predominately planetary‐derived plasma has a variety of names. The region below that middle boundary and the top of the ionosphere also does not have a uniformly used name. There are several other regions and boundaries that also have naming confusion. The various terms that are currently used in the literature for these subjects are identified and discussed; regions and boundaries that have well‐settled names are not discussed nor are the details of the physics involved. Key Points: The near‐Mars plasma environment is often either called (1) the induced Martian magnetosphere or (2) the solar wind interaction with MarsThis interaction has a variety of confusingly overlapping terms for some of its boundaries and regionsTerms that are currently unsettled in the literature for such areas are identified and discussed [ABSTRACT FROM AUTHOR]

Experimental studies on Hg 0 removal by CuCl 2 modified magnetospheres (Cu 6 –MF) injection were performed in an entrained flow reactor system. The factors affecting the Hg 0 removal efficiency were investigated, including the initial Hg 0 concentration, sorbent concentration in flue gas, sorbent particle size, sorbent residence time in flue gas, and flue gas temperature. The results indicated that, as the raise of initial Hg 0 concentration, the Hg 0 removal efficiency increased. The Hg 0 removal efficiency also increased with the increase of sorbent residence time and sorbent concentration in flue gas. When the residence time was 1.61 s and the sorbent concentration was 1.09 g/m 3 , the Hg 0 removal efficiency could reach to 80.6%. However, with the further increase of residence time and sorbent concentration, the Hg 0 removal efficiency did not increase continuously. The smaller particle size was favorable for the Hg 0 removal. In the industrial application, the particle size could be selected as 45–74 μm when comprehensively considering the Hg 0 removal efficiency, the cost of sorbent preparation, and other factors. The acid flue gases have negligible impacts on Hg 0 removal, while moisture plays a slightly negative role in Hg 0 removal under SFG atmosphere. With the superior Hg 0 removal performance, the Cu 6 –MF sorbent may presents great potentials for Hg 0 removal in coal-fired power plants. [ABSTRACT FROM AUTHOR]

The short, 7.2-day orbital period of Cassini’s Ring Grazing Orbits (RGO) provided an opportunity to monitor how fast the effects of an intense magnetospheric storm-time period (days 336–343/2016) propagated into Saturn’s electron radiation belts. Following the storms, Cassini’s MIMI/LEMMS instrument detected a transient extension of the electron radiation belts that in subsequent orbits moved towards the inner belts, intensifying them in the process. This intensification was followed by an equally fast decay, possibly due to the rapid absorption of MeV electrons by the planet’s main rings. Surprisingly, all this cycle was completed within four RGOs, effectively in less than a month. That is considerably faster than the year-long time scales of Saturn’s proton radiation belt evolution. In order to explain this difference, we propose that electron radial transport is partly controlled by the variability of global scale electric fields which have a fixed local time pointing. Such electric fields may distort significantly the orbits of a particular class of energetic electrons that cancel out magnetospheric corotation due to their westward gradient and curvature drifts (termed “corotation-resonant” or “local-time stationary” electrons) and transport them radially between the ring current and the radiation belts within several days and few weeks. The significance of the proposed process is highlighted by the fact that corotation resonance at Saturn occurs for electrons of few hundred keV to several MeV. These are the characteristic energies of seed electrons from the ring current that sustain the radiation belts of the planet. Our model’s feasibility is demonstrated through the use of a simple test-particle simulation, where we estimate that uniform but variable electric fields with magnitudes lower that 1.0 mV/m can lead to a very efficient transport of corotation resonant electrons. Such electric fields have been consistently measured in the magnetosphere, and here we provide additional evidence showing that they may be constantly present all the way down to the outer edge of Saturn’s main rings, further supporting our model. The implications of our findings are not limited to Saturn. Corotation resonance at Jupiter occurs for electrons with energies above about 10 MeV throughout the quasi-dipolar, energetic particle-trapping region of the magnetosphere. The proposed process could in principle then lead to rapid transport and adiabatic acceleration electrons into ultra-relativistic energies. The observation by Galileo’s EPD/LEMMS instrument of an intense Jovian acceleration event at the orbital distance of Ganymede during the mission’s C22 orbit, when  > 11 MeV electron fluxes were preferentially enhanced, provides additional support to our transport model and insights on the origin of that orbit’s extreme energetic electron environment. Finally, if the mode of radial transport that we describe here is a dominant one, radial diffusion coefficients ( D LL ) would be subject to strong energy, pitch angle and species dependencies. [ABSTRACT FROM AUTHOR]

Quite recently, it has been suggested that the interaction of the solar wind with Mercury results in the variation in the solar wind velocity in the Earth’s neighborhood during inferior conjunctions with Mercury. This suggestion has important implications both on the plasma physics of the interplanetary space and on the space weather forecast. In this study we have attempted to answer a question of whether the claim is properly tested. We confirm that there are indeed ups and downs in the profile of the solar wind velocity measured at the distance of 1 AU from the Sun. However, the characteristic attribute of the variation in the solar wind velocity during the inferior conjunctions with Mercury is found to be insensitive to the phase of the solar cycles, contrary to an earlier suggestion. We have found that the cases of the superior conjunctions with Mercury and of even randomly chosen data sets rather result in similar features. Cases of Venus are also examined, where it is found that the ups and downs with a period of ~ 10 to 15 days can be also seen. We conclude, therefore, that those variations in the solar wind velocity turn out to be a part of random fluctuations and have nothing to do with the relative position of inner planets. At least, one should conclude that the solar wind velocity is not a proper observable modulated by inner planets at the distance of 1 AU from the Sun in the Earth’s neighborhood during inferior conjunctions.

The Hg 0 removal capacities of magnetospheres from fly ash collected from different power plants were investigated at a wide temperature range of 100–400 °C. The relationship between Hg 0 removal efficiency ( η T ) and iron content/species of magnetospheres was investigated. The magnetospheres attained the optimal Hg 0 removal capacity at 250 °C. The reaction temperature played an important role in Hg 0 adsorption and oxidation behaviors. At low reaction temperature (100 °C and 150 °C), the adsorption of Hg 0 played a predominant role in Hg 0 removal, while the Hg 0 removal mainly depended on the Hg 0 oxidation capacity at high temperature (200–400 °C). The Hg 0 removal capacity increased with the increase of iron content. The percentage of ferrospinel and hematite in magnetospheres is a key factor for determining the Hg 0 removal capacity as well. Hydrogen fluoride (HF) could remove the glass-phase materials on the magnetospheres and the active iron species embedded in the glass phase could be exposed and accessible. After fluorinated by HF, the Hg 0 removal capacity increased in different degree for different magnetospheres, which depended on the content of active iron species in raw magnetospheres. [ABSTRACT FROM AUTHOR]

The magnetospheres around neutron stars should be very particular because of their strong magnetic field and rapid rotation. A study of the pulsar magnetospheres is of crucial importance since it is the key issue to understand how energy outflow to the exterior is produced. In this paper, we discuss magnetohydrodynamic processes in the pulsar magnetosphere. We consider in detail the properties of magnetohydrodynamic waves that can exist in the magnetosphere and their instabilities. These instabilities lead to formation of magnetic structures and can be responsible for short-term variability of the pulsar emission. [ABSTRACT FROM AUTHOR]

Quasi-thermal noise spectroscopy is an efficient tool for measuring in situ macroscopic plasma properties in space, using a passive wave receiver at the ports of an electric antenna. This technique was pioneered on spinning spacecraft carrying very long dipole antennas in the interplanetary medium-like ISEE-3 and Ulysses-whose geometry approached a 'theoretician's dream.' The technique has been extended to other instruments in various types of plasmas on board different spacecraft and will be implemented on several missions in the near future. Such extensions require different theoretical modelizations, involving magnetized, drifting, or dusty plasmas with various particle velocity distributions and antennas being shorter, biased, or made of unequal wires. We give new analytical approximations of the plasma quasi-thermal noise (QTN) and study how the constraints of the real world in space can (or cannot) be compatible with plasma detection by QTN spectroscopy. We consider applications to the missions Wind, Cassini, BepiColombo, Solar Orbiter, and Parker Solar Probe. [ABSTRACT FROM AUTHOR]

We live on a very special planet in a very special solar system. Our planet has a benign climate. Our star has several habitable planets and is not so active as to inhibit the exploration and future colonization of these planets. In this short paper we review how the solar wind interacts with the planets, what factors matter in this interaction, and how active is our star. [ABSTRACT FROM AUTHOR]

XFTRISTAN is a graphical user interface (GUI) for the tridimensional particle in cell (PIC) code called TRISTAN. The TRISTAN code has been widely used to investigate the kinetic nature of space plasma processes applied to problems ranging from solar wind-earth interaction to magnetic reconnection topology. This first XFTRISTAN version provides an easy way to enter input parameters, visualization of fields and particles, several diagnostic tools and apaper, we present the advantages and capabilities of our GUI and first simulation results.

We analyze the planetary ion, solar wind, interplanetary magnetic field (IMF), and solar extreme ultraviolet (EUV) irradiance data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to quantify the variation in ion escape with solar EUV irradiance. With relatively strict constraints on the upstream solar wind and IMF conditions, we divide the planetary ion data into 4 subsets with different solar EUV conditions to estimate ion escape rates. The results show that the total ion escape rate may increase nonlinearly with solar EUV irradiance and eventually approach an asymptotic limit as EUV increases. Further analysis on different ion species, escape channels, and energy ranges show that the dependence on solar EUV varies between these different ion populations. We also find that the spatial distributions of ion density and velocity vary between high and low solar EUV conditions, which is likely caused by the variations of electromagnetic field distributions. These results suggest that as solar EUV controls the ion production and affects the ion distributions near Mars, it will in turn influence the electromagnetic field distributions and thus affect the acceleration of escaping ions. This feedback mechanism may limit the total ion escape rate as solar EUV increases under constrained solar wind and IMF conditions. • The total Martian ion escape rate may show a nonlinear increase with solar EUV irradiance. • The fractions of higher energy escaping ions decrease while those of lower energy ions increase with solar EUV. • Solar EUV affects ion acceleration by changing the electromagnetic field distributions near Mars. [ABSTRACT FROM AUTHOR]

The mineralogy, morphology, and chemical composition of magnetic fractions separated from fly ashes (FAs) originating from Greek lignite-burning power plants was investigated. The oral bioaccessibility of potentially harmful elements (PHEs) from the fly ash magnetic fractions (FAMFs) was also assessed using in vitro gastrointestinal extraction (BARGE Unified Bioaccessibility Method, UBM). The FAMFs isolated were in the range 4.6-18.4%, and their mass specific magnetic susceptibility ranged from 1138 × 10 to 1682 × 10 m/kg. XRD analysis and Mossbauer spectroscopy indicated that the dominant iron species were Fe-rich aluminosilicate glass along with magnetite, hematite, and maghemite (in decreasing order). The raw FAs exhibited differences in their chemical composition, indicating the particularity of every lignite basin. The elemental contents of FAMFs presented trends with fly ash type; thus, the FAMFs of high-Ca FAs were enriched in siderophile (Cr, Co, Ni) and lithophile (Cs, Li, Rb) elements and those separated from low-Ca FAs were presented depleted in chalcophile elements. Based on UBM extraction tests, the PHEs were more bioaccessible from the non-magnetic components of the FAs compared to the magnetic ones; however, the bioaccessible fractions estimated for the FAMFs were exceeding 40 % in many cases. Arsenic was found to be significantly bioaccessible (median ~ 80 %) from FAMFs despite the lower As contents in the magnetic fraction. [ABSTRACT FROM AUTHOR]

Venus is gradually losing some of its atmosphere in the form of ions through its induced magnetotail. Some of these ions have been reported previously to flow back to the planet. Proposed drivers are magnetic reconnection and deflection of pickup ions in the magnetic field. We analyze protons and oxygen ions with eV to keV energies acquired by the ASPERA-4/IMA instrument throughout the entire Venus Express mission. We find that venusward flowing ions are important in the sense that their density and deposition rate into the atmosphere is of the same order of magnitude as the density and escape rate of downtail flowing ions. Our analysis shows that during strong EUV irradiance, which occurs during solar maximum, the flux of venusward flowing protons is weaker and of oxygen ions is stronger than during weak irradiance. Since such a behavior was observed when tracing oxygen ions through a MHD model, the ultimate driver of the venusward flowing ions may simply be the magnetic field configuration around Venus. Although the pure downtail oxygen flux stays mostly unchanged for all observed EUV conditions, the increase in venusward oxygen flux for high irradiance results in a lower net atmospheric escape rate. Venusward bulk flows are mostly found in locations where the magnetic field is weak relative to the interplanetary conditions. Although a weak field is generally an indicator of proximity to the magnetotail current sheet, these flows do not cluster around current sheet crossings, as one may expect if they would be driven by magnetic reconnection. [ABSTRACT FROM AUTHOR]

A survey of Cassini MIMI/LEMMS data acquired between 2004 and 2015 has led to the identification of 13 energetic electron microsignatures that can be attributed to particle losses on one of the several faint rings of the planet. Most of the signatures were detected near L-shells that map between the orbits of Mimas and Enceladus or near the G-ring. Our analysis indicates that it is very unlikely for these signatures to have originated from absorption on Mimas, Enceladus or unidentified Moons and rings, even though most were not found exactly at the L-shells of the known rings of the saturnian system (G-ring, Methone, Anthe, Pallene). The lack of additional absorbers is apparent in the L-shell distribution of MeV ions which are very sensitive for tracing the location of weakly absorbing material permanently present in Saturn’s radiation belts. This sensitivity is demonstrated by the identification, for the first time, of the proton absorption signatures from the asteroid-sized Moons Pallene, Anthe and/or their rings. For this reason, we investigate the possibility that the 13 energetic electron events formed at known saturnian rings and the resulting depletions were later displaced radially by one or more magnetospheric processes. Our calculations indicate that the displacement magnitude for several of those signatures is much larger than the one that can be attributed to radial flows imposed by the recently discovered noon-to-midnight electric field in Saturn’s inner magnetosphere. This observation is consistent with a mechanism where radial plasma velocities are enhanced near dusty obstacles. Several possibilities are discussed that may explain this observation, including a dust-driven magnetospheric interchange instability, mass loading by the pick-up of nanometer charged dust grains and global magnetospheric electric fields induced by perturbed orbits of charged dust due to the act of solar radiation pressure. Indirect evidence for a global scale interaction between the magnetosphere and Saturn’s faint rings that may drive such radial transport processes may also exist in previously reported measurements of plasma density by Cassini. Alternative explanations that do not involve enhanced plasma transport near the rings require the presence of a transient absorbing medium, such as E-ring clumps. Such clumps may form at the L-shell range where microsignatures have been observed due to resonances between charged dust and corotating magnetospheric structures, but remote imaging observations of the E-ring are not consistent with such a scenario. [ABSTRACT FROM AUTHOR]

The regeneration performance of spent catalyst after mercury removal as well as the involved reaction mechanism was investigated. The effects of restoration with or without O 2 and/or HCl, O 2 and HCl concentration, regeneration temperature, and heating rate on regeneration performance were studied, respectively. The results suggested that two steps were essential in the regeneration process: (1) releasing the sulfur and mercury species adsorbed on the catalyst; (2) restoring the surface chemistry of catalyst by O 2 and HCl. Optimal regeneration performance of spent catalyst was attained after thermal desorption at 400 °C and following by the restoration of O 2 and HCl. The changes in surface chemistry of catalyst revealed that the sulfur and mercury species could be fully released by heating at 400 °C, and the deactivated adsorption sites was exposed. With the assistance of O 2 and HCl, the surface chemistry of Cu and Cl was restored close to original CuCl 2 . Four cycles of mercury adsorption−catalyst regeneration showed that the mercury removal capacity did not vary appreciably with respect to fresh catalyst after multiple regeneration. [ABSTRACT FROM AUTHOR]