Ion Escape Research Articles

Venusian ion escape under extreme conditions: A dynamic pressure and temperature simulation study

We investigated the response of the Venusian atmospheric ion escape under the effect of interplanetary coronal mass ejections (ICMEs) using the Latmos Hybrid Simulation (LatHyS). In particular, we focused on the influence of extreme ICME dynamic pressures and temperatures, with the temperature being a parameter that has not been extensively studied in the past. Simulations were performed for two different dynamic pressures and three different temperatures. For the case of the dynamic pressure simulations, a density and a velocity enhancement event were studied separately. The H$^ $ and O$^ $ ion escape was then examined and compared for different escape channels. In both dynamic pressure enhancement cases, we find that there is no clear dependence of the O$^ $ ion escape on the dynamic pressure, which is consistent with observations. On the other hand, the temperature of the incoming solar wind positively influences the H$^ $ and O$^ $ ion escape. This is attributed in part to the enhanced gyroradius of the particles, which allows them to penetrate deeper into the planet's atmosphere.

Mars’s induced magnetosphere can degenerate

AbstractThe interaction between planets and stellar winds can lead to atmospheric loss and is, thus, important for the evolution of planetary atmospheres1. The planets in our Solar System typically interact with the solar wind, whose velocity is at a large angle to the embedded stellar magnetic field. For planets without an intrinsic magnetic field, this interaction creates an induced magnetosphere and a bow shock in front of the planet2. However, when the angle between the solar wind velocity and the solar wind magnetic field (cone angle) is small, the interaction is very different3. Here we show that when the cone angle is small at Mars, the induced magnetosphere degenerates. There is no shock on the dayside, only weak flank shocks. A cross-flow plume appears and the ambipolar field drives planetary ions upstream. Hybrid simulations with a 4° cone angle show agreement with observations by the Mars Atmosphere and Volatile Evolution mission4 and Mars Express5. Degenerate, induced magnetospheres are complex and not yet explored objects. It remains to be studied what the secondary effects are on processes like atmospheric loss through ion escape.

Atmospheric ion escape and solar wind deposition as a function of planetary radius

ABSTRACT We explore the ability of an unmagnetized planet to retain an atmosphere as a function of its radius. We use a particle-in-cell hybrid code to simulate the global plasma interaction of unmagnetized terrestrial planets at 1 au under average solar wind conditions. We vary the radius of the planet $(R_\mathrm{ p})$ from Mars-sized ($3390 \ \mathrm{km}$) to super-Earth-sized ($9390 \ \mathrm{km}$). We inject hydrogen and oxygen ion outflows from the ionosphere and quantify how the ion escape, recirculation, solar wind deposition, and net atmospheric mass flux vary as a function of planetary radius. We find that as the radius and the corresponding ionospheric outflow rate are varied, the fraction of outflowing $\mathrm{ H^+}$ that escapes remains at $15.5\pm 1.0{{\ \rm per\, cent}}$, while the rest recirculates back towards the planet. The fraction of produced $\mathrm{ O^+}$ that escapes from a Mars-sized planet is $27\pm 1{{\ \rm per\, cent}}$, and decreases to $7\pm 1{{\ \rm per\, cent}}$ for super-Earth, suggesting that smaller planets are less able to retain heavy ions. We find, however, that larger planets have lower solar wind deposition fractions because their bow shocks are at greater distances from the surface of the planet. The ionospheric outflow rate at which mass deposition is equal to mass escape is found to be proportional to $R_\mathrm{ p}^2$. Lastly, we propose that the bulk gyration of the solar wind at the induced magnetosphere can lead to differential escape trajectories of light and heavy ions.

Earth's ambipolar electrostatic field and its role in ion escape to space.

Cold plasma of ionospheric origin has recently been found to be a much larger contributor to the magnetosphere of Earth than expected1-3. Numerous competing mechanisms have been postulated to drive ion escape to space, including heating and acceleration by wave-particle interactions4 and a global electrostatic field between the ionosphere and space (called the ambipolar or polarization field)5,6. Observations of heated O+ ions in the magnetosphere are consistent with resonant wave-particle interactions7. By contrast, observations of cold supersonic H+ flowing out of the polar ionosphere8,9 (called the polar wind) suggest the presence of an electrostatic field. Here we report the existence of a +0.55 ± 0.09 V electric potential drop between 250 km and 768 km from a planetary electrostatic field (E∥⊕ = 1.09 ± 0.17 μV m-1) generated exclusively by the outward pressure of ionospheric electrons. We experimentally demonstrate that the ambipolar field of Earth controls the structure of the polar ionosphere, boosting the scale height by 271%. We infer thatthis increases the supply of cold O+ ions to the magnetosphere by more than 3,800%, in which other mechanisms such as wave-particle interactions can heat and further accelerate them to escape velocity. The electrostatic field of Earth is strong enough by itself to drive the polar wind9,10 and is probably the origin of the cold H+ ion population1 that dominates much of the magnetosphere2,3.

The Effect of the Interplanetary Magnetic Field Clock Angle and the Latitude Location of the Intense Crustal Magnetic Field on the Ion Escape at Mars: An MHD Simulation Study

AbstractIn this paper, using a three‐dimensional multifluid MHD model, we studied the effects of the interplanetary magnetic field (IMF) clock angle and the latitude position of the intense crustal magnetic field (ICMF) on the escape of ions O+, , and at Mars. The main results are as follows: (a) The IMF clock angle affects the ion escape at Mars. When the ICMF is on the dayside, the ion escape rate reaches a maximum at the IMF clock angles close to 60°–90° and a minimum at the IMF clock angles close to 120°–150°, because the ICMF can change the topology of the magnetic field and affect the interaction between the solar wind and Mars. The difference between the maximum and minimum ion escape rates due to the IMF clock angle can reach over 50%. (b) Compared with the −ESW hemisphere, the escape flux of and in the +ESW hemisphere is more significant. However, O+ generally has a larger escape flux in the −ESW hemisphere. The different results in the ±ESW hemispheres might be due to the larger distribution of the hot oxygen corona, which changes the flow pattern of O+. (c) The latitude location of the ICMF can also affect the ion escape. When the ICMF is on the dayside, as the subsolar point varies from 25°S to 25°N, that is, the intense crustal magnetic field position keeps shifting southward, the ion escape rate shows a gradual increase.

Closed magnetic topology in the Venusian magnetotail and ion escape at Venus

Venus, lacking an intrinsic global dipole magnetic field, serves as a textbook example of an induced magnetosphere, formed by interplanetary magnetic fields (IMF) enveloping the planet. Yet, various aspects of its magnetospheric dynamics and planetary ion outflows are complex and not well understood. Here we analyze plasma and magnetic field data acquired during the fourth Venus flyby of the Parker Solar Probe (PSP) mission and show evidence for closed topology in the nightside and downstream portion of the Venus magnetosphere (i.e., the magnetotail). The formation of the closed topology involves magnetic reconnection—a process rarely observed at non-magnetized planets. In addition, our study provides an evidence linking the cold Venusian ion flow in the magnetotail directly to magnetic connectivity to the ionosphere, akin to observations at Mars. These findings not only help the understanding of the complex ion flow patterns at Venus but also suggest that magnetic topology is one piece of key information for resolving ion escape mechanisms and thus the atmospheric evolution across various planetary environments and exoplanets.

Direct Observations of Magnetic Reconnections at the Magnetopause of the Martian Mini‐Magnetosphere

AbstractWhile Mars lacks a global intrinsic magnetic field, it does exhibit crustal magnetic anomalies (mostly in its Southern Hemisphere). These crustal magnetic anomalies directly interact with solar wind, which forms a mini‐magnetosphere and a region denoted the mini‐magnetopause. Using magnetic field and plasma measurements from the Mars Atmosphere and Volatile Evolution, we report a novel case of magnetic reconnection at the Martian mini‐magnetopause. In this process, protons and oxygen ions from the Martian atmosphere were accelerated during reconnection and likely escaped along the outflow direction. Magnetic reconnection may occur between the interplanetary magnetic field and crustal magnetic fields at the Martian mini‐magnetopause, which contributes to planetary ion escape, solar wind entering the mini‐magnetosphere and the evolution of magnetic topology in the dayside Martian mini‐magnetosphere.

MESSENGER Observations of Mercury's Planetary Ion Escape Rates and Their Dependence on True Anomaly Angle

AbstractThis study investigates the escape of Mercury's sodium‐group ions (Na+‐group, including ions with m/q from 21 to 30 amu/e) and their dependence on true anomaly angle (TAA), that is, Mercury's orbital phase around the Sun, using measurements from MESSENGER. The measurements are categorized into solar wind, magnetosheath, and magnetosphere, and further divided into four TAA intervals. Na+‐group ions form escape plumes in the solar wind and magnetosheath, with higher fluxes along the solar wind's motional electric field. The total escape rates vary from 0.2 to 1 × 1025 atoms/s with the magnetosheath being the main escaping region. These rates exhibit a TAA dependence, peaking near the perihelion and similar during Mercury's remaining orbit. Despite Mercury's tenuous exosphere, Na+‐group ions escape rate is comparable to other inner planets. This can be attributed to several processes, including that Na+‐group ions may include several ion species, efficient photoionization frequency for elements within Na‐group, etc.

Simulations of the hydrogen and deuterium thermal and non-thermal escape at Mars at Spring Equinox

We present simulations of the thermal and nonthermal escape processes for H and D, under atomic, molecular and ion forms at Mars during spring equinox. These processes include Jeans escape, several photochemical reactions and the escape associated to the solar wind interaction with Mars. While the hydrogen escape is dominated by the atomic Jeans escape, we find that the deuterium escape is dominated by the photochemical atomic escape. Ions escape represent only 10% of the total escape for both species and is mostly due to charge exchange between neutral and solar wind protons. Including all the processes, we find a D/H fractionation factor (D/H escape ratio divided by the D/H atmospheric ratio) f = 0.04, with a main uncertainty associated to the elastic collisional cross sections needed to accurately derive the photochemical escape rate. Using this fractionation factor and considering a 30 m exchangeable reservoir of water, the average hydrogen escape rate needed to fractionate the Martian water from its primordial value to its current D/H value during the last 4.5 Gyr is ∼1.0 × 1028 s−1 which is larger than the current average escape rate (∼ 2 × 1026 s−1).

Enhanced Acceleration and Escape of Hydrogen Pickup Ions Upstream from Mars by Interplanetary Shocks

The pickup process of newly ionized hydrogen (H) from the Martian extended exosphere represents an important H+ escape channel on Mars. It is generally believed that interplanetary (IP) shocks can accelerate the pickup ions and, in turn, affect the pickup process. However, the underlying processes inherent to the acceleration are not yet fully understood. Here, we concentrate on the dynamic processes involved in acceleration arising from IP shock compression. We examine two typical IP shock events characterized by a sudden increase in the average energy of upstream H+ pickup ions across the shock. The H+ pickup ions continuously enter the field of view of Supra-Thermal And Thermal Ion Composition or Solar Wind Ion Analyzer on board the Mars Atmosphere and Volatile EvolutioN spacecraft in a narrow angular range. Moreover, they correspond to a similar part of their respective ring distributions in velocity space. By comparing measured and theoretical H+ pickup ion energies, we attribute the more energetic H+ pickup ions to the enhanced convection electric field acceleration caused by the shock compression. An increase in the guiding center drift speed across the shock implies a higher escape rate of the H+ pickup ions. Furthermore, the pitch-angle scattering could facilitate the escape of the higher energy H+ pickup ions from Mars. The results may shed light on the understanding of the energization and escape of planetary pickup ions in the solar system.

Effects of an Intrinsic Magnetic Field on Ion Escape From Ancient Mars Based on MAESTRO Multifluid MHD Simulations

AbstractIon escape has played a key role in atmospheric loss on ancient Mars due to intense solar activity. Under the existence of a strong global intrinsic magnetic field, as expected on ancient Mars, differential flows between different ion species can be important for ion escape. To assess effects of differential flows, we here developed a new global multifluid magnetohydrodynamics model with a cubed sphere grid named Multifluid Atmospheric Escape Simulations Toward Real elucidatiOn (MAESTRO). A test simulation under present‐day Mars conditions showed solar wind‐Mars interactions, for example, plasma boundaries, ionospheric profiles, and tailward outflows, consistent with observations and simulation studies. We then conducted multifluid and multispecies simulations with six different dipole field strengths under ancient Mars conditions. The multifluid cases show asymmetric outflow distributions with respect to the solar wind convection electric field, as pointed out by previous studies on present‐day Mars. Compared with multispecies cases, the multifluid representation increases the escape rates of O2+ and CO2+ by more than two orders of magnitude in the strong dipole field cases where the cusp outflow is dominant. The O+ escape rate is slightly lower in the multifluid cases with no or weak dipole field due to suppression of ion pickup in the −E hemisphere, while it is reduced by one order of magnitude in the strongest dipole field case. The existence of a dipole field can reduce the total escape rate by a factor of six. The impact on atmospheric evolution is diminished but still significant.

Enhanced Oxygen Ion Outflow at Earth and Mars due to the Concurrent Impact of a Stream Interaction Region

One of the major processes that solar wind drives is the outflow and escape of ions from the planetary atmospheres. The major ion species in the upper ionospheres of both Earth and Mars is O+, and hence it is more likely to dominate the escape process. On Earth, due to a strong intrinsic magnetic field, the major ion outflow pathways are through the cusp, polar cap, and the auroral oval. In contrast, Mars has an induced magnetosphere, where the ionosphere is in direct contact with the shocked solar wind plasma. Therefore, physical processes underlying the ion energization and escape rates are expected to be different on Mars as compared to Earth. In the current work, we study the near-simultaneous ion outflow event from both Earth and Mars during the passage of a stream interaction region/high-speed stream (SIR/HSS) during 2016 May, when both the planets were approximately aligned on the same side of the Sun. The SIR/HSS propagation was recorded by spacecraft at the Sun–Earth L1 point and Mars Express at 1.5 au. During the passage of the SIR, the dayside and nightside ion outflows at Earth were observed by Van Allen Probes and Magnetospheric Multiscale Mission orbiters, respectively. At Mars, the ion energization at different altitudes was observed by the STATIC instrument on board the MAVEN orbiter. We observe evidence for the enhanced ion outflow from both Earth and Mars during the passage of the SIR, and identify the dominant drivers of the ion outflow.

Dynamics of Sputtered Neutral Sodium Atoms in the Near‐Mercury Space

AbstractThe solar wind sputtering in the magnetospheric polar cusp is an important source of heavy atoms in Mercury’s exosphere and magnetosphere. However, the majority of ejected atoms are neutral, undergoing an extended period before photoionization occurs. In this study, we employ an ab initio simulation to investigate the behavior of sodium (Na) atoms prior to their photoionization. Our results reveal that overall only approximately 2.7% of the sputtered atoms contribute to magnetospheric ions, while the vast majority of these ions (∼82.9%) escape into interplanetary space. The remaining fraction (14.4%) eventually returns to the planetary surface. For Na atoms ionized inside the magnetosphere, a larger proportion of Na+ (53.5%) is supplied to the magnetotail compared to the polar cusp (39.4%), which is due to the tailward acceleration caused by solar radiation. Additionally, the remaining Na+ (7.1%) contributes to the dayside ring current region, as demonstrated by the observation of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. Our research introduces a perspective on Na+ transport in the magnetosphere that complements and coexists with traditional mechanisms.

Ionospheric Plasma Transported Into the Martian Magnetosheath

AbstractHeavy cold ions at Mars are gravitationally bound to the planet unless some process provides energy to them. Observations show that cold (<20 eV) and dense (∼>1 cm−3) O+/O2+ ions with bulk velocities equal to energies ∼1 keV can reach deep into the nightside Martian magnetosheath. These ions are co‐located with a change of the sign of the sunward component of the magnetic field. This magnetic field topology implies the persistence of a localized planetary ions escape channel associated with draped magnetic field lines that are convecting tailward. The observed ion populations propagate approximately in the same direction as surrounding magnetosheath flow and are likely to be almost unheated ionospheric ions from low altitudes. The paper discusses planetary ion energization via Hall electric field originated from ions and electron separation associated with magnetic field curvature.

Rapid removal of ofloxacin with peroxymonosulfate activation process mediated by Co3O4/Sludge-derived biochar composite: Unveiling the enhancement of biochar

In this study, sludge-derived biochar loaded Co3O4 composite (Co3O4@SDBC) were successfully synthesized through cobalt impregnation and secondary calcination of sludge-derived biochar precursors. The experimental results demonstrated that the Co3O4@SDBC catalyst performed exceptionally well for peroxymonosulfate (PMS) activation, with a high degradation efficiency (>99 %) of ofloxacin (OFL) within 10 min under the optimal conditions (a catalyst dose of 0.10 g•L−1, a PMS dose of 0.975 mM and an initial pH = 6.4), and showed good adaptability across a broad pH spectrum, under the interference of the anions and humic acid (HA), as well as in various water matrices. The results of quenching experiments revealed that the non-radical pathway (especially 1O2 and electron transfer) was the dominated reactive ingredients in the PMS activation process induced by Co3O4@SDBC. Notably, the online electrochemical tests and density functional theory (DFT) results indicated the presence of biochar carrier not only effectively lowered the escape of Co ions, while enhanced the steadiness of Co3O4@SDBC, but also accelerated the electron transfer, promoted the adsorption and cleavage of PMS, facilitated the redox cycle between Co(II) and Co(III), reduced the reaction energy barriers simultaneously, thereby making it more favourable for the generation of 1O2. Furthermore, the toxicity assessment suggested that the cumulative toxicity of OFL decreased throughout degradation. Overall, this work mechanistically revealed the enhancement of biochar on the Co3O4@SDBC catalyst, offering a viable method to activate PMS for antibiotic removal and achieving a mutually beneficial strategy for sludge waste resource utilization and environmental remediation.

The Energetic Oxygen Ion Beams in the Martian Magnetotail Current Sheets: Hints From the Comparisons Between Two Types of Current Sheets

AbstractUsing data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we explore the plasma properties of Martian magnetotail current sheets (CS), to further understand the solar wind interaction with Mars and ion escape. There are some CS exhibit energetic oxygen ions that show narrow beam structures in the energy spectrum, which primarily occurs in the hemisphere where the solar wind electric field (Esw) is directed away from the planet. On average, these CS have a higher escaping flux than that of the CS without energetic oxygen ion beams, suggesting different roles in ion escape. The CS with energetic oxygen ion beams exhibits different proton and electron properties to the CS without energetic oxygen ion beams, indicating their different origins. Our analysis suggests that the CS with energetic oxygen ion beams may result from the interaction between the penetrated solar wind and localized oxygen ion plumes.

Ionospheric density depletions around crustal fields at Mars and their connection to ion frictional heating

Abstract. Mars' ionosphere is formed through ionization of the neutral atmosphere by solar irradiance, charge exchange, and electron impact. Observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft have shown a highly dynamic ionospheric layer at Mars impacted by loss processes including ion escape, transport, and electron recombination. The crustal fields at Mars can also significantly modulate the ionosphere. We use MAVEN data to perform a statistical analysis of density depletions of ionospheric species (O+, O2+, and electrons) around crustal fields. Events mostly occur when the crustal magnetic fields are radial, outward, and with a mild preference towards east in the planetocentric coordinates. We show that events near crustal fields are typically accompanied by an increase in suprathermal electrons within the depletion, either throughout the event or as a short-lived electron beam. However, no correlation between the changes in the bulk electron densities and suprathermal electron density variations is observed. Our analysis indicates that the temperature of the major ionospheric species, O2+, increases during most of the density depletion events, which could indicate that some ionospheric density depletions around crustal fields are a result of ion frictional heating.

Viroporins Manipulate Cellular Powerhouses and Modulate Innate Immunity.

Viruses have a wide repertoire of molecular strategies that focus on their replication or the facilitation of different stages of the viral cycle. One of these strategies is mediated by the activity of viroporins, which are multifunctional viral proteins that, upon oligomerization, exhibit ion channel properties with mild ion selectivity. Viroporins facilitate multiple processes, such as the regulation of immune response and inflammasome activation through the induction of pore formation in various cell organelle membranes to facilitate the escape of ions and the alteration of intracellular homeostasis. Viroporins target diverse membranes (such as the cellular membrane), endoplasmic reticulum, and mitochondria. Cumulative data regarding the importance of mitochondria function in multiple processes, such as cellular metabolism, energy production, calcium homeostasis, apoptosis, and mitophagy, have been reported. The direct or indirect interaction of viroporins with mitochondria and how this interaction affects the functioning of mitochondrial cells in the innate immunity of host cells against viruses remains unclear. A better understanding of the viroporin-mitochondria interactions will provide insights into their role in affecting host immune signaling through the mitochondria. Thus, in this review, we mainly focus on descriptions of viroporins and studies that have provided insights into the role of viroporins in hijacked mitochondria.

Role of Planetary Radius on Atmospheric Escape of Rocky Exoplanets

Large-scale characterization of exoplanetary atmospheres is on the horizon, thereby making it possible in the future to extract their statistical properties. In this context, by using a well-validated model in the solar system, we carry out 3D magnetohydrodynamic simulations to compute nonthermal atmospheric ion escape rates of unmagnetized rocky exoplanets as a function of their radius based on fixed stellar radiation and wind conditions. We find that the atmospheric escape rate is, unexpectedly and strikingly, a nonmonotonic function of the planetary radius R and that it evinces a maximum at R ∼ 0.7 R ⊕. This novel nonmonotonic behavior may arise from an intricate trade-off between the cross-sectional area of a planet (which increases with size, boosting escape rates) and its associated escape velocity (which also increases with size but diminishes escape rates). Our results could guide forthcoming observations because worlds with certain values of R (such as R ∼ 0.7 R ⊕) might exhibit comparatively higher escape rates when all other factors are constant.

Enhancing the hydrogen ion adsorption capacity to improve the performance of an aqueous zinc ion battery of V2O5

In acidic aqueous zinc-ion batteries (AZIBs), the insertion and escape of zinc ions are always accompanied by hydrogen ions, but the effect of hydrogen ion adsorption capacity on the performance of zinc-ion batteries has hardly been discussed. Herein, a sea urchin-like Ni-V2O5 is obtained to estimate the effect of hydrogen ion adsorption capacity. Due to the interaction of nickel with oxygen, Ni-V2O5 exhibits an excellent hydrogen ion adsorption capacity compared to pristine V2O5. The improvement in hydrogen ion adsorption capacity directly optimizes the charge and discharge performance of AZIB. The Zn//Ni-V2O5 battery exhibits a specific capacity of 313 mA h g−1 and a high energy density of 240 Wh kg−1 at 0.5 A g−1. This provides a new viewpoint for the charging and discharging mechanism of AZIBs.