Magnetosphere Research Articles

The Internal Structure and Dynamics of Jupiter Unveiled by a High‐Resolution Magnetic Field and Secular Variation Model

AbstractUnique information about the dynamo process acting at Jupiter can be inferred by modeling and interpreting its magnetic field. Using the fluxgate magnetometer measurements acquired during the 4 years of the Juno mission, we derive a magnetic field model which describes simultaneously the main field and the secular variation (SV) up to spherical harmonic degrees 16 and 8, respectively. Apart from the Earth's, this is the first time another planetary magnetic field along with its time variation is described to such a high degree. We use properties of the power spectrum of the static field to infer the upper boundary of the dynamo convective region at 0.830 ± 0.022 Jupiter radius. The SV and correlation times are relatively comparable to the Earth's and indicate that the field is dominated by advection. The field and SV morphologies suggest zonal as well as non‐zonal deep fluid motions.

Effects of the Planetary Field on the Accretion Process of a Planet in the Final Stage of Giant Planet Formation

Recent studies suggest that the magnetic field may play an important role in the formation of giant planets during the final stage of the formation process. In this paper, we construct a circumplanetary system around a planet that is in the final formation stage to investigate the effects of the planetary magnetic field on the accretion process of the planet at this stage. We find that at the early times of our magneto-hydrodynamic (MHD) simulation, the magnetic loops connecting the planet and the circumplanetary material inflate upward due to the build-up of the toroidal field pressure with magnetic islands forming inside the loops, which changes the flow pattern above the planet in comparison with the hydrodynamic case. We find that a low-density gap, which is produced by the strong magnetic pressure, appears along the disk’s surface and expands as the system evolves. Accompanied by the accretion flow above the disk surface, the disk surface field lines can reconnect with the magnetic loops anchored on the planet. Thus, the material above the disk’s surface can permeate into the loops anchored on the planet via reconnection and can be accreted to the planet through the loops. Comparing the results in the hydrodynamic and MHD simulations, we find that the mass accretion rate and the angular momentum transport rate from the infalling gas to the planet do not change apparently when the effects of the magnetic field are included, but these rates from the circumplanetary disk to the planet increase significantly by an order of magnitude.

Analytic Approach to the Late Stages of Giant Planet Formation

This paper constructs an analytic description for the late stages of giant planet formation. During this phase of evolution, the planet gains the majority of its final mass through gas accretion at a rapid rate. This work determines the density and velocity fields for material falling onto the central planet and its circumplanetary disk, and finds the corresponding column density of this infalling envelope. We derive a steady-state solution for the surface density of the disk as a function of its viscosity (including the limiting case where no disk accretion occurs). Planetary magnetic fields truncate the inner edge of the disk and determine the boundary conditions for mass accretion onto the planet from both direct infall and from the disk. The properties of the forming planet and its circumplanetary disk are determined, including the luminosity contributions from infall onto the planet and disk surfaces, and from disk viscosity. The radiative signature of the planet formation process is explored using a quasi-spherical treatment of the emergent spectral energy distributions. The analytic solutions developed herein show how the protoplanet properties (envelope density distribution, velocity field, column density, disk surface density, luminosity, and radiative signatures) vary with input parameters (instantaneous mass, orbital location, accretion rate, and planetary magnetic field strength).

Core@Shell structured coal fly ash Magnetospheres@C/g-C3N4 for degradation of Rh B via photo-Fenton catalysis

The photo-Fenton technology has shown widespread application potential in the degradation of wastewater. Herein, solid waste coal fly ash magnetospheres (MS) composed of a large amount of Fe 3 O 4 and Fe 2 O 3 were used as raw materials to prepare a novel photo-Fenton catalyst MS@C/g-C 3 N 4 . The SEM characterization results showed MS@C had a special core@shell structure with many micro-cracks, and for MS@C/g-C 3 N 4 , the g-C 3 N 4 nanosheets not only intersperse in the cracks of MS@C, but also adhere to the surface of MS@C. The FTIR characterization results showed the little changes of the peaks corresponding to -CN heterocycles in MS@C/g-C 3 N 4 may be caused by the interaction between g-C 3 N 4 and MS@C. The photo-Fenton performance of MS@C/g-C 3 N 4 composites was evaluated by degrading of Rh B. MS@C/g-C 3 N 4 composites displayed the highest rate constant (0.1532 min −1 ) than MS@C (0.0671 min −1 ) and pure g-C 3 N 4 (0.0018 min −1 )as well as samples of mixture of MS@C and g-C 3 N 4 (0.0745 min −1 ) due to the presence of the synergistic effect between photocatalysis and Fenton reaction. The effects of carbon shells thickness, H 2 O 2 concentration, Rh B concentration and pH value on the photo-Fenton degradation of Rh B by MS@C/g-C 3 N 4 were studied. The ICP results showed that the carbon shells had an inhibitory effect on the leaching of iron ions, and the optimal photo-Fenton degradation conditions were H 2 O 2 concentration of 50 mmol/L, Rh B concentration of 100 mg/L and pH = 3. The recycle experiment showed that the degradation rate of MS@C/g-C 3 N 4 composites was only slightly decreased about 5% after four cycles, and the XRD results for the fresh MS@C/g-C 3 N 4 and used MS@C/g-C 3 N 4 showed that there were no obvious changes occurred in the crystal structure after fourth cycle, which indicated that MS@C/g-C 3 N 4 possessed excellent stability. The main active species were •OH and h + in this system, and a possible photo-Fenton mechanism was proposed. The carbon shells (coated on MS) could enhance the separation efficiency of photogenerated electron-hole pairs of g-C 3 N 4 . In addition, the leached iron ions in MS@C/g-C 3 N 4 could be anchored to the surface by the pyridine nitrogen in g-C 3 N 4 to form Fe-N bonds, which could accelerate the transfer of electrons and be regarded as the active site in the Fenton reaction. • A novel photo-Fenton catalyst MS@C/g-C 3 N 4 was synthesized. • The thickness of carbon shells is controllable. • The high load of MS@C to g-C 3 N 4 is due to the special core@shell structure. • The catalyst showed excellent degradation ability for Rh B. • The enhanced catalytic performance is due to synergistic effect.

Multispecies MHD Study of Ion Escape at Ancient Mars: Effects of an Intrinsic Magnetic Field and Solar XUV Radiation

AbstractIon escape is one of the key processes responsible for drastic climate change on ancient Mars. Ion escape is affected by the solar X‐ray and EUV (X‐ray and extreme ultraviolet (XUV)) flux, the solar wind, and the presence of a planetary intrinsic magnetic field, all of which was much different at ancient Mars. We investigated how the presence and strength of a dipole field affects the ion escape under 50 or 10 times higher solar XUV flux and strong solar wind with multispecies magnetohydrodynamics model. The results showed two opposite effects on the escape rates, which is associated with the pressure ratio of the dipolar magnetic pressure at the equatorial surface to the solar wind dynamic pressure. The escape rates increase by up to a factor of 6 for O2+ and CO2+ but change little for O+ if the pressure ratio is below 0.1. On the other hand, the escape rates decrease by more than one order of magnitude for the three ions if the pressure ratio is above 0.1. The threshold can be described by the pressure balance between the solar wind flow and the dipole field at high latitudes, where the ionospheric outflow emerges in the unmagnetized cases. The effects on the escape rates are stronger under lower solar XUV cases. The total escape rate reaches 1027 s−1 in the unmagnetized case, which may lead to a large contribution to atmospheric loss at ancient Mars, but it can be reduced by an order of magnitude in the presence of a dipole field.

Plasma Imaging, LOcal Measurement, and Tomographic Experiment (PILOT): A Mission Concept for Transformational Multi-Scale Observations of Mass and Energy Flow Dynamics in Earth’s Magnetosphere

We currently do not understand the fundamental physical processes that govern mass and energy flow through the Earth’s magnetosphere. Knowledge of these processes is critical to understanding the mass loss rate of Earth’s atmosphere, as well as for determining the role that a planetary magnetic field plays in atmospheric retention, and therefore habitability, for Earth-like planets beyond the solar system. Mass and energy flow processes are challenging to determine at Earth in part because Earth’s planetary magnetic field creates a complex “system of systems” composed of interdependent plasma populations and overlapping spatial regions that perpetually exchange mass and energy across a broad range of temporal and spatial scales. Further, the primary mass carrier in the magnetosphere is cold plasma (as cold as ∼0.1 eV), which is invisible to many space-borne instruments that operate in the inner magnetosphere. The Plasma Imaging LOcal and Tomographic experiment (PILOT) mission concept, described here, provides the transformational multi-scale observations required to answer fundamental open questions about mass and energy flow dynamics in the Earth’s magnetosphere. PILOT uses a constellation of spacecraft to make radio tomographic, remote sensing, and in-situ measurements simultaneously, fully capturing cold plasma mass dynamics and its impact on magnetospheric systems over an unprecedented range of spatial and temporal scales. This article details the scientific motivation for the PILOT mission concept as well as a potential mission implementation.

A 3D Physics‐Based Particle Model of the Venus Oxygen Corona: Variations With Solar Activity

AbstractDue to Venus not having a substantial planetary magnetic field the fast‐flowing solar wind plasma can propagate to regions close to the planet. Therefore, thermal atomic oxygen in the thermosphere, hot oxygen in the corona, and the resulting pickup oxygen ions are essential for determining the overall interaction of the planet with plasma of the ambient solar wind. To investigate this complex system, we have initiated a project where a combination of Venus Thermosphere General Circulation Model (VTGCM) and Adaptive Mesh Particle Simulator (AMPS) codes are used to determine the variability of the ”hot” O corona depending on the solar conditions. Here we present the results of modeling Venus' oxygen corona using the VTGCM ionosphere/thermosphere and AMPS kinetic particle models. VTGCM produces a self‐consistent calculation of the thermosphere/ionosphere, providing the spatial distributions of the dominant species. That is further used in AMPS’ modeling of Venus' exosphere (a) to specify the source of the newly created hot O atoms produced by dissociative recombination of ions and (b) to account for thermalization of these energetic oxygen atoms as they propagate in the upper thermosphere. The altitude distribution of hot O calculated for the solar maximum conditions agree well with Pioneer Venus Orbiter observations of the oxygen corona. The modeling that we have performed for the solar minimum conditions indicates a decrease of the oxygen density in the corona by almost a factor of six compared to that at solar maximum. That is consistent with the non‐detection of the oxygen corona from Venus Express. As expected, the solar moderate case is between the solar maximum and minimum cases.

Quasistatic magnetoconvection with a tilted magnetic field

Convection is the primary driver of magnetic fields in planets and stars. This self-generated magnetic field can then react back on the underlying convection by influencing its structure and dynamics. Numerical simulations are used to explore the convective dynamics in the presence of an externally imposed magnetic field that has a component perpendicular to gravity. New flow regimes are identified and their quantitative behavior is analyzed.

Impact of electro-magneto-hydrodynamics in radiative flow of nanofluids between two rotating plates

Heat transfer improvement using electro-magneto hydrodynamics is a technique that can result in significant heat exchanger reduction as well as “on-demand” heat transfer. Electrohydrodynamic (EHD) is a multidisciplinary science that studies how fluids interact with electric fields or charges. It has been found applications in many areas such as EHD pump, EHD enhanced heat transfer, microelectromechanical systems (MEMS) and other industrial processes. MHD offers a broad array of applications for researchers in astrophysics, planetary magnetic fields, generators, flow meters, metallurgy, metal dispersion (granulation), ship propulsion, crystal development, magnetic filtration, and fusion reactors. Investigation of the mass and heat transfer properties of hybrid nanofluid Transformeroil+TiO2+Fe3O4 in three dimensions is considered. In this research, cumulative effects of magnetic and electric hydrodynamic are examined between two rotating plates in viscous hybrid nanofluid. To generate the hybrid nanofluid, transformer oil is utilized as a base fluid in the nanoparticles TiO2 andFe3O4. Using a similarity approach, the flow model in the form of PDEs is reduced to a system of dimensionless ODEs. The obtained equations are solved by using a shooting (bvp4c) method to attain a numeric solution. Reynolds number, rotational factors and effects of magnetic and electric properties in hydrodynamics have all been researched and argued about thermal efficiency, drag force, and mass flux. Numerical data of Nusselt number, Sherwood number, and drag forces are calculated. By minimizing the influence of physical constraints, the hybrid nanofluid enhances heat transfer rate and mass transport.

Разработка технологии комплексной переработки шлаков Златоустовского металлургического завода

Introduction. Currently, many metallurgical companies in Russia are experiencing difficulties with the supply of raw materials. One of the solutions to this problem is the involvement in the reuse of secondary resources that are formed in metallurgical processing. So there are more than 15 million tons of them on the territory of Zlatoust steel Mill. The development of metallurgical slag processing technology will partially solve the problem of the company’s own raw material base. Methodology. To develop an effective technology for complex processing of metallurgical slags of Zlatoust steel Mill four samples were taken from various sections of slag dumps. Research results and discussion. The work studied the chemical and mineralogical composition of samples, conducted studies on the enrichment of slags. To study the enrichment of metallurgical slags by the magnetic enrichment method, studies have been carried out, including separation of material with a size of -100 +40 mm on a drum separator and material with a size of -40+0 mm on a separator in a suspended state. The results show that products made of a material with a size of -100+40 mm meet the requirements for direct use in blast furnace production. and products obtained from a size class of -40+0 mm meet the requirements of agglomeration production. The chemical analysis of the obtained products after magnetic separation in a suspended state indicates significant nickel content in the magnetic separation tails of the sample with a size of -40+0 mm. The study of the microstructure of the sample showed that the size of nickel inclusions is on average 1 mm. In this work studies have been carried out on the grinding of tails to a size of less than 1 mm and enrichment on gravity apparatuses. Studies comparing the results of metallurgical slag enrichment on a concentration table and a centrifugal concentrator have shown significantly higher efficiency of slag separation on a centrifugal concentrator. Conclusions. The obtained results on the enrichment of metallurgical slags ofZlatoust steel Mill allows us to recommend a comprehensive processing technology. As a result of enrichment the following products are obtained: magnetic product 1 with a mass fraction of iron 88.4% when extracting 35.2%. magnetic product 2 with a mass fraction of iron 42.7% when extracting 12.4% and nickel-containing concentrate with a mass fraction of nickel 4.85% when extracting 67.9%.

Artificial Triangular Points by Lorentz Force in the Restricted Three-Body Problem

The restricted three body problem was outlined. The acceleration due to planetary magnetic field, in terms of space craft’s orbital elements, was analysed. The conditions for calculating the liberation points including the mutual gravitational attraction and the effect of Lorentz acceleration were derived for the case of circular planer restricted three bodies. The stability of the solution for the artificial Lorentz triangular liberation points was studied. Finally, numerical investigation for the case of Sun-Jupiter system was calculated as case study. The results show the ability of changing the position of the triangular liberation points by an order from 10−7 to 10−6 for the dimensionless x, y coordinates and distance r from Jupiter. This is equivalent to about hundreds of Kilometers which is considerable.

Distribution of water phase near the poles of the Moon from gravity aspects

Our Moon periodically moves through the magnetic tail of the Earth that contains terrestrial ions of hydrogen and oxygen. A possible density contrast might have been discovered that could be consistent with the presence of water phase of potential terrestrial origin. Using novel gravity aspects (descriptors) derived from harmonic potential coefficients of gravity field of the Moon, we discovered gravity strike angle anomalies that point to water phase locations in the polar regions of the Moon. Our analysis suggests that impact cratering processes were responsible for specific pore space network that were subsequently filled with the water phase filling volumes of permafrost in the lunar subsurface. In this work, we suggest the accumulation of up to ~ 3000 km3 of terrestrial water phase (Earth’s atmospheric escape) now filling the pore spaced regolith, portion of which is distributed along impact zones of the polar regions of the Moon. These unique locations serve as potential resource utilization sites for future landing exploration and habitats (e.g., NASA Artemis Plan objectives).

Dispersion and Focusing of Cosmic Rays in Magnetospheres

Abstract Simulating the irradiation of planetary atmospheres by cosmic ray particles requires, among others, the ability to understand and to quantify the interactions of charged particles with planetary magnetic fields. Here we present a process that is very often ignored in such studies: the dispersion and focusing of cosmic ray trajectories in magnetospheres. The calculations were performed using our new code CosmicTransmutation, which has been developed to study cosmogenic nuclide production in meteoroids and planetary atmospheres and which includes the computation of the irradiation spectrum on top of the atmosphere. Here we discuss effects caused by dispersion and focusing of cosmic ray particle trajectories.

Magnetospheric response to solar wind forcing: ultra-low-frequency wave–particle interaction perspective

Abstract. Solar wind forcing, e.g., interplanetary shock and/or solar wind dynamic pressure pulses impacting Earth's magnetosphere, manifests many fundamental important space physics phenomena, including producing electromagnetic waves, plasma heating, and energetic particle acceleration. This paper summarizes our present understanding of the magnetospheric response to solar wind forcing in the aspects of radiation belt electrons, ring current ions and plasmaspheric plasma physics based on in situ spacecraft measurements, ground-based magnetometer data, magnetohydrodynamics (MHD) and kinetic simulations. Magnetosphere response to solar wind forcing is not just a “one-kick” scenario. It is found that after the impact of solar wind forcing on Earth's magnetosphere, plasma heating and energetic particle acceleration started nearly immediately and could last for a few hours. Even a small dynamic pressure change in interplanetary shock or solar wind pressure pulse can play a non-negligible role in magnetospheric physics. The impact leads to generation of a series of waves, including poloidal-mode ultra-low-frequency (ULF) waves. The fast acceleration of energetic electrons in the radiation belt and energetic ions in the ring current region response to the impact usually contains two contributing steps: (1) the initial adiabatic acceleration due to the magnetospheric compression, (2) followed by the wave–particle resonant acceleration dominated by global or localized poloidal ULF waves excited at various L-shells. Generalized theory of drift and drift–bounce resonance with growth- or decay-localized ULF waves has been developed to explain in situ spacecraft observations. The wave-related observational features like distorted energy spectrum, “boomerang” and “fishbone” pitch angle distributions of radiation belt electrons, ring current ions and plasmaspheric plasma can be explained in the framework of this generalized theory. It is worth pointing out here that poloidal ULF waves are much more efficient at accelerating and modulating electrons (fundamental mode) in the radiation belt and charged ions (second harmonic) in the ring current region. The results presented in this paper can be widely used in solar wind interacting with other planets such as Mercury, Jupiter, Saturn, Uranus and Neptune and other astrophysical objects with magnetic fields.

The toroidal field surfaces in the standard poloidal-toroidal representation of magnetic field

The representation of magnetic field as a sum of a toroidal field and a poloidal field has not rarely been used in astrophysics, particularly in relation to stellar and planetary magnetism. In this representation, each toroidal field line lies entirely in a surface, which is named a toroidal field surface. The poloidal field is represented by the curl of another toroidal field and it threads a stack of toroidal field surfaces. If the toroidal field surfaces are either spheres or planes, the poloidal-toroidal (PT) representation is known to have a special property that the curl of a poloidal field is again a toroidal field . We name a PT representation with this property a standard PT representation while one without the property is called a generalized PT representation. In this paper, we have addressed the question whether there are other toroidal field surfaces allowing a standard PT representation than spheres and planes. We have proved that in a three dimensional Euclidean space, there can be no standard toroidal field surfaces other than spheres and planes, which render the curl of a poloidal field to be a toroidal field.

Saturn's Weather‐Driven Aurorae Modulate Oscillations in the Magnetic Field and Radio Emissions

AbstractThe Cassini spacecraft revealed that Saturn's magnetic field displayed oscillations at a period originally thought to match the planetary rotation rate but later found not to. One of many proposed theories predicts that a polar twin‐cell neutral weather system drives this variation, producing observable differences in flows within Saturn's ionosphere. Here, using spectral observations of auroral emission lines taken by the Keck Observatory's Near Infrared Echelle Spectrograph (Keck‐NIRSPEC) in 2017, we derive ion line‐of‐sight velocity maps after grouping spectra into rotational quadrants matching phases of the planetary magnetic field. We measure 0.5 km s−1 wind systems in the ionosphere consistent with predicted neutral twin‐vortex flow patterns. These findings demonstrate that neutral winds in Saturn's polar regions cause the rotational period, as determined via the magnetic field, to exhibit differences and time variabilities relative to the planet's true period of rotation in a process never before seen within planetary atmospheres.

Stratification in planetary cores by liquid immiscibility in Fe-S-H

Liquid-liquid immiscibility has been widely observed in iron alloy systems at ambient pressure and is important for the structure and dynamics in iron cores of rocky planets. While such previously known liquid immiscibility has been demonstrated to disappear at relatively low pressures, here we report immiscible S(±Si,O)-rich liquid and H(±C)-rich liquid above ~20 GPa, corresponding to conditions of the Martian core. Mars’ cosmochemically estimated core composition is likely in the miscibility gap, and the separation of two immiscible liquids could have driven core convection and stable stratification, which explains the formation and termination of the Martian planetary magnetic field. In addition, we observed liquid immiscibility in Fe-S-H(±Si,O,C) at least to 118 GPa, suggesting that it can occur in the Earth’s topmost outer core and form a low-velocity layer below the core-mantle boundary.

Searching for Stellar and Planetary Emission in Large Field-of-view Radio Sky Surveys

Abstract Detection of low-frequency (≤1.4 GHz) radio emission from stellar and planetary systems can lead to new insights into stellar activity, extrasolar space weather, and planetary magnetic fields. In this work, we investigate three large field-of-view surveys at 74 MHz, 150 MHz, and 1.4 GHz, as well as a myriad of multiwavelength ancillary data, to search for radio emission from about 2600 stellar objects, including about 800 exoplanetary systems, 600 nearby low-mass stars, and 1200 young stellar objects located in the Taurus and Upper Scorpius star-forming regions. The selected sample encompasses stellar spectral types from B to L and distances between 5 and 300 pc. We report the redetection of five stars at 1.4 GHz, one of which also shows emission at 150 MHz. Four of these are low- and intermediate-mass young stars, and one is the evolved star α Sco. We also observe radio emission at the position of a young brown dwarf at 1.4 GHz and 150 MHz. However, due to the large astrometric uncertainty of radio observations, a follow-up study at higher angular resolution would be required to confirm whether the observed emission originates from the brown dwarf itself or a background object. Notably, all of the selected radio sources are located in nearby star-forming regions. Furthermore, we use image stacking and statistical methods to derive upper limits on the average quiescent radio luminosity of the families of objects under investigation. These analyses provide observational constraints for large-scale searches for current and ongoing low-frequency radio emissions from stars and planets.

A New Model of Jupiter's Magnetic Field at the Completion of Juno's Prime Mission

AbstractA spherical harmonic model of the magnetic field of Jupiter is obtained from vector magnetic field observations acquired by the Juno spacecraft during 32 of its first 33 polar orbits. These Prime Mission orbits sample Jupiter's magnetic field nearly uniformly in longitude (∼11° separation) as measured at equator crossing. The planetary magnetic field is represented with a degree 30 spherical harmonic and the external field is approximated near the origin with a simple external spherical harmonic of degree 1. Partial solution of the underdetermined inverse problem using generalized inverse techniques yields a model (“JRM33”) of the planetary magnetic field with spherical harmonic coefficients reasonably well determined through degree and order 13. Useful information regarding the field extends through degree 18, well fit by a Lowes' spectrum with a dynamo core radius of 0.81 Rj, presumably the outer radius of the convective metallic hydrogen region. This new model provides a most detailed view of a planetary dynamo and evidence of advection of the magnetic field by deep zonal winds in the vicinity of the Great Blue Spot (GBS), an isolated and intense patch of flux near Jupiter's equator. Comparison of the JRM33 and JRM09 models suggests secular variation of the field in the vicinity of the GBS during Juno's nearly 5 years of operation in orbit about Jupiter. The observed secular variation is consistent with the penetration of zonal winds to a depth of ∼3,500 km where a flow velocity of ∼0.04 ms−1 is required to match the observations.

Xenon isotope constraints on ancient Martian atmospheric escape

Trapped, paleoatmospheric xenon (Xe) in the Martian regolith breccia NWA 11220 is mass-dependently fractionated relative to solar Xe by 16.2 ± 2.7‰/amu. These data indicate that fractionation of atmospheric Xe persisted for hundreds of millions of years after planetary formation. Such a protracted duration of atmospheric Xe mass fractionation, which is particularly striking when compared to the non-fractionated state of Martian atmospheric krypton (Kr), cannot be easily reconciled with Xe escape as a neutral atom in a neutral hydrodynamic hydrogen wind. However, Xe escape as an ion coupled to a partially ionized hydrogen or oxygen wind provides a simple solution to problems associated with the neutral escape hypothesis. Ionic Xe escape requires a sufficiently high escape flux of a carrier ion (H+ or O+) and probably requires a structured planetary magnetic field to channel the flow. The end of Xe escape from Mars could be attributed to waning hydrogen sources from volcanic outgassing or from interactions of reduced impactors with surface water and ice. Alternatively, if Xe ions were driven off by O+, the end of Xe escape could be attributed to the decay of solar extreme ultra-violet radiation.