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On June 23rd 2022, BepiColombo performed its second gravity assist maneuver (MFB2) at Mercury. Just like the first encounter with Mercury that took place on October 1st 2021, the spacecraft approached the planet from dusk-nightside to dawn-dayside down to an extremely close distance (within about 200 km altitude from the planet surface). Even though BepiColombo is in a so-called “stacked configuration” during cruise, meaning that the instruments cannot be fully operated yet, these instruments can still make interesting observations. Particularly, despite their limited field-of-view, the particle sensors allow us to get a hint on the ion composition and dynamics very close to the planet well before the forthcoming orbit insertion around Mercury in December 2025. In this study, we present observations of the Mass Spectrum Analyzer (MSA) at Mercury during MFB2. MSA is part of the low energy sensors of the Mercury Plasma Particle Experiment (MPPE) consortium (PI: Y. Saito), which is a comprehensive instrumental suite for plasma, high-energy particle and energetic neutral atom measurements (Saito et al., 2021) onboard the Mercury Magnetospheric Orbiter (Mio). MSA is a “reflectron” time-of-flight spectrometer that provides information on the plasma composition and the three-dimensional distribution functions of ions with energies up to ~ 38 keV/q and masses up to ~ 60 amu (Delcourt et al., 2016). In this study, we show that both H+ and He2+ ions in the 1-10 keV range are present throughout the innermost magnetosphere near closest approach. In addition, during this MFB2 sequence, MSA observations provide evidences of He+ ions with energies of several hundreds of eVs. These ions likely originate from the planet exosphere and are rapidly circulated within the magnetosphere. During the outbound sequence of MFB2, MSA measurements also reveal copious amounts of keV protons of solar wind origin that propagate upstream after being reflected from the bow shock.

令和4年度宇宙科学に関する室内実験シンポジウム（2023年3月6日-7日. オンライン開催), 2023 Symposium on Laboratory Experiment for Space Science (March 6-7, 2023. Online Meeting), 資料番号:SA6000187035, レポート番号: 35

During the flybys of Mercury and Venus the ion spectrometers onboard the BepiColombo spacecraft observed enhanced fluxes of ions with energies of less than 50eV. Often these fluxes showed a characteristic double-band spectral shape in energy. We interpret these ion fluxes as being caused by ionized water molecules outgassing from the spacecraft. The double-band structure may be caused by a specific feature of the spacecraft potential: for a negatively charged spacecraft electrons will be rejected from the spacecraft and may form a negative space charge at distance given by the Debye length. This space charge may contribute to a separation of the observed ion fluxes into an inner and an outer source resulting in a double-band energy distribution. We show results of a particle-in-cell simulation supporting this interpretation.

The ESA-JAXA BepiColombo mission will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with the solar wind, radiation, and interplanetary dust. Many scientific instruments onboard the two spacecraft will be completely, or partially devoted to study the near-space environment of Mercury as well as the complex processes that govern it. Many issues remain unsolved even after the MESSENGER mission that ended in 2015. The specific orbits of the two spacecraft, MPO and Mio, and the comprehensive scientific payload allow a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone, or by previous missions. These joint observations are of key importance because many phenomena in Mercury's environment are highly temporally and spatially variable. Examples of possible coordinated observations are described in this article, analysing the required geometrical conditions, pointing, resolutions and operation timing of different BepiColombo instruments sensors., Comment: 78 pages, 14 figures, published

The Mass Spectrum Analyzer (MSA) will perform in-situ observations of ions and magnetic fields around Phobos as part of the Martian Moons eXploration (MMX) mission to investigate the origin of the Martian moons and physical processes in the Martian environment. MSA consists of an ion energy mass spectrometer and two magnetometers which will measure velocity distribution functions and mass/charge distributions of low-energy ions and magnetic field vectors, respectively. For the MMX scientific objectives, MSA will observe solar wind ions, those scattered at the Phobos surface, water-related ions generated in the predicted Martian gas torus, secondary ions sputtered from Phobos, and escaping ions from the Martian atmosphere, while monitoring the surrounding magnetic field. MSA will be developed from previous instruments for space plasma missions such as Kaguya, Arase, and BepiColombo/Mio to contribute to the MMX scientific objectives.

International audience; BepiColombo Mio (previously called MMO: Mercury Magnetospheric Orbiter) was successfully launched by Ariane 5 from Kourou, French Guiana on October 20, 2018. The Mercury Plasma/Particle Experiment (MPPE) is a comprehensive instrument package onboard Mio spacecraft used for plasma, high-energy particle and energetic neutral atom measurements. It consists of seven sensors including two Mercury Electron Analyzers (MEA1 and MEA2), Mercury Ion Analyzer (MIA), Mass Spectrum Analyzer (MSA), High Energy Particle instrument for electron (HEP-ele), High Energy Particle instrument for ion (HEP-ion), and Energetic Neutrals Analyzer (ENA). Significant efforts were made pre-flight to calibrate all of the MPPE sensors at the appropriate facilities on the ground. High voltage commissioning of MPPE analyzers was successfully performed between June and August 2019 and in February 2020 following the completion of the low voltage commissioning in November 2018. Although all of the MPPE analyzers are now ready to begin observation, the full service performance has been delayed until Mio’s arrival at Mercury. Most of the fields of view (FOVs) of the MPPE analyzers are blocked by the thermal shield surrounding the Mio spacecraft during the cruising phase. Together with other instruments on Mio including Magnetic Field Investigation (MGF) and Plasma Wave Investigation (PWI) that measure plasma field parameters, MPPE will contribute to the comprehensive understanding of the plasma environment around Mercury when BepiColombo/Mio begins observation after arriving at the planet Mercury in December 2025.

International audience

The ESA-JAXA BepiColombo mission to Mercury will provide simultaneous measurements from two spacecraft, offering an unprecedented opportunity to investigate magnetospheric and exospheric particle dynamics at Mercury as well as their interactions with solar wind, solar radiation, and interplanetary dust. The particle instrument suite SERENA (Search for Exospheric Refilling and Emitted Natural Abundances) is flying in space on-board the BepiColombo Mercury Planetary Orbiter (MPO) and is the only instrument for ion and neutral particle detection aboard the MPO. It comprises four independent sensors: ELENA for neutral particle flow detection, Strofio for neutral gas detection, PICAM for planetary ions observations, and MIPA, mostly for solar wind ion measurements. SERENA is managed by a System Control Unit located inside the ELENA box. In the present paper the scientific goals of this suite are described, and then the four units are detailed, as well as their major features and calibration results. Finally, the SERENA operational activities are shown during the orbital path around Mercury, with also some reference to the activities planned during the long cruise phase.

International audience; Processes driven by unsteady reconnection can efficiently accelerate particles in many astrophysical plasmas. An example is the reconnection jet fronts in an outflow region. We present evidence of suprathermal ion acceleration between two consecutive reconnection jet fronts observed by the Magnetospheric Multiscale mission in the terrestrial magnetotail. An earthward propagating jet is approached by a second faster jet. Between the jets, the thermal ions are mostly perpendicular to magnetic field, are trapped, and are gradually accelerated in the parallel direction up to 150 keV. Observations suggest that ions are predominantly accelerated by a Fermi-like mechanism in the contracting magnetic bottle formed between the two jet fronts. The ion acceleration mechanism is presumably efficient in other environments where jet fronts produced by variable rates of reconnection are common and where the interaction of multiple jet fronts can also develop a turbulent environment, e.g., in stellar and solar eruptions.

International audience; Mercury has a unique and complex space environment with its weak global magnetic field, intense solar wind, tenuous exosphere, and magnetospheric plasma particles. This complex system makes Mercury an excellent science target to understand effects of the solar wind to planetary environments. In addition, investigating Mercury’s dynamic magnetosphere also plays a key role to understand extreme exoplanetary environment and its habitability conditions against strong stellar winds. BepiColombo, a joint mission to Mercury by the European Space Agency and Japan Aerospace Exploration Agency, will address remaining open questions using two spacecraft, Mio and the Mercury Planetary Orbiter. Mio is a spin-stabilized spacecraft designed to investigate Mercury’s space environment, with a powerful suite of plasma instruments, a spectral imager for the exosphere, and a dust monitor. Because of strong constraints on operations during its orbiting phase around Mercury, sophisticated observation and downlink plans are required in order to maximize science outputs. This paper gives an overview of the Mio spacecraft and its mission, operations plan, and data handling and archiving.

International audience; BepiColombo Mio, also known as the Mercury Magnetospheric Orbiter (MMO), is intended to conduct the first detailed study of the magnetic field and environment of the innermost planet, Mercury, alongside the Mercury Planetary Orbiter (MPO). This orbiter has five payload groups; the MaGnetic Field Investigation (MGF), the Mercury Plasma Particle Experiment (MPPE), the Plasma Wave Investigation (PWI), the Mercury Sodium Atmosphere Spectral Imager (MSASI), and the Mercury Dust Monitor (MDM). These payloads operate through the Mission Data Processor (MDP) that acts as an integrated system for Hermean environmental studies by the in situ observation of charged and energetic neutral particles, magnetic and electric fields, plasma waves, dust, and the remote sensing of radio waves and exospheric emissions. The MDP produces three kinds of coordinated data sets: Survey (L) mode for continuous monitoring, Nominal (M) mode for standard analyses of several hours in length (or more), and Burst (H) mode for analysis based on 4-20-min-interval datasets with the highest cadence. To utilize the limited telemetry bandwidth, nominal- and burst-mode data sets are partially downlinked after selections of data based on L- or L/M-mode data, respectively. Burst-mode data can be taken at preset timings, or by onboard automatic triggering. The MDP functions are implemented and tested on the ground as well as cruising spacecraft; they are responsible for conducting full scientific operations aboard spacecraft.

International audience; We investigate the transport of planetary ions in the magnetospheric flanks of Mercury. In situ measurements from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft show evidences of Kelvin-Helmholtz instability development in this region of space, due to the velocity shear between the downtail streaming flow of solar wind originating protons in the magnetosheath and the magnetospheric populations. Ions that originate from the planet exosphere and that gain access to this region of space may be transported across the magnetopause along meandering orbits. We examine this transport using single-particle trajectory calculations in model Magnetohydrodynamics simulations of the Kelvin-Helmholtz instability. We show that heavy ions of planetary origin such as Na may experience prominent nonadiabatic energization as they E × B drift across large-scale rolled up vortices. This energization is controlled by the characteristics of the electric field burst encountered along the particle path, the net energy change realized corresponding to the maximum E × B drift energy. This nonadiabatic energization also is responsible for prominent scattering of the particles toward the direction perpendicular to the magnetic field.

Energetic particles with energies from tens of keV to a few hundreds keV are frequently observed in the Earth's magnetotail. Here we study, by means of a test particle numerical simulation, the acceleration of different ion species (H$^{+}$, He$^{+}$, He$^{++}$, and O$^{n+}$ with $n=1$--$6$) in the presence of transient electromagnetic perturbations. All the considered ions develop power-law tails at high energies, except for O$^+$ ions. This is strongly correlated to the time that the particle spend in the current sheet. Ion acceleration is found to be proportional to the charge state, while it grows in a weaker way with the ion mass. We find that O$^{5+/6+}$ can reach energies higher than $500$ kev. These results may explain the strong oxygen acceleration observed in the magnetotail.

International audience; In this article we aim to highlight the problems related to the structure and stability of the comparatively thin current sheets that were relatively recently discovered by space missions in the magnetospheres of the Earth and planets, as well as in the solar wind. These magnetoplasma structures are universal in collisionless cosmic plasmas and can play a key role in the processes of storage and release of energy in the space environment. The development of a self-consistent theory for these sheets in the Earth's magnetosphere, where they were first discovered, has a long and dramatic history. Solution of the problem of the thin current sheet structure and stability become possible in the framework of a kinetic quasi-adiabatic approach required to explain their embedding and metastability properties. It was found that the structure and stability of current structures are completely determined by the nonlinear dynamics of plasma particles. Theoretical models have been developed to predict many properties of these structures and interpret many experimental observations in planetary magnetospheres and the heliosphere.

Observations from the MESSENGER spacecraft have considerably enhanced our understanding of the plasma environment at Mercury. In particular, measurements from the Fast Imaging Plasma Spectrometer (FIPS) provide evidences of a variety of ion species of planetary origin (He+, O+, Na+) in the northern dayside cusp and in the nightside plasma sheet. A more comprehensive view of Mercury's plasma environment will be provided by the Bepi Colombo mission that will be launched in 2018. Onboard the Bepi Colombo MMO spacecraft, the MPPE (Mercury Plasma/Particle Experiment) consortium gathers different sensors dedicated to particle measurements. Among these sensors, the Mass Spectrum Analyzer (MSA) is the instrument dedicated to plasma composition analysis. It consists of a top-hat for energy analysis followed by a Time-Of-Flight (TOF) chamber to derive the ion mass. Taking advantage of the spacecraft rotation, MSA will measure three-dimensional distribution functions in one spin (4 s), from energies characteristic of exospheric populations (in the eV range) up to plasma sheet energies (up to ~38 keV/q). A notable feature of the MSA instrument is that the TOF chamber is polarized with a linear electric field that leads to isochronous TOFs and enhanced mass resolution (typically, m/∆m ≈ 40 for ions with energies up to 13 keV/q). At Mercury, this capability is of paramount importance to thoroughly characterize the wide variety of ion species originating from the planet surface. It is thus anticipated that MSA will provide unprecedented information on ion populations in the Hermean environment and hence improve our understanding of the coupling processes at work.

Non-adiabatic energization and transport of planetary ions in the vicinity of Kelvin-Helmholtz (KH) vortices at Mercury are statistically investigated using a magnetohydrodynamic model combined with a test particle tracing technique. The measurements from the MErcury Surface, Space ENvironment, Geochemistry, and Ranging spacecraft show signatures of KH waves in the magnetospheric flanks, especially on the duskside. We examine here the energization and transport of heavy ions of planetary origin such as Na + associated with the growth of the KH instability on both the dawn and dusk sides of the magnetosphere, and for both northward and southward interplanetary magnetic field configurations. We find that in all cases those planetary ions in the magnetosphere can be accelerated non-adiabatically with a level of acceleration larger on the dawnside. The transport of those ions is controlled by the convection electric field in the magnetosheath. Those planetary ions when picked up in the duskside magnetosphere where the KH waves have been mainly observed at Mercury stagnate inside the magnetosphere and, hence, are not expected to escape. The present study indicates that these ions may likely stay inside the magnetosphere and sputter the planetary surface on the duskside preferentially, being the source of secondary neutrals from the planetary surface.

Erreur sur l'affiliation : Dominique Delcourt : 1, 21 : Laboratoire de Physique des Plasmas, Ecole Polytechnique, CNRS, france2, LPC2E, UMR7328, CNRS, Université d'Orléans, 45071 Orléans Cedex 2; International audience; Magnetic field dipolarizations are often observed in the magnetotail during substorms. These generally include three temporal scales: (1) actual dipolarization when the normal magnetic field changes during several minutes from minimum to maximum level; (2) sharp Bz bursts (pulses) interpreted as the passage of multiple dipolarization fronts with characteristic time scales < 1 min, and (3) bursts of electric and magnetic fluctuations with frequencies up to electron gyrofrequency occurring at the smallest time scales (≤ 1 s). We present a numerical model where the contributions of the above processes (1)-(3) in particle acceleration are analyzed. It is shown that these processes have a resonant character at different temporal scales. While O+ ions are more likely accelerated due to the mechanism (1), H+ ions (and to some extent electrons) are effectively accelerated due to the second mechanism. High-frequency electric and magnetic fluctuations accompanying magnetic dipolarization as in (3) are also found to efficiently accelerate electrons.

International audience; The spatial distributions of different ion species are useful indicators for plasma sheet dynamics. In this statistical study based on 7 years of Cluster observations, we establish the spatial distributions of oxygen ions and protons at energies from 274 to 955 keV, depending on geomagnetic and solar wind (SW) conditions. Compared with protons, the distribution of energetic oxygen has stronger dawn-dusk asymmetry in response to changes in the geomagnetic activity. When the interplanetary magnetic field (IMF) is directed southward, the oxygen ions show significant acceleration in the tail plasma sheet. Changes in the SW dynamic pressure (Pdyn) affect the oxygen and proton intensities in the same way. The energetic protons show significant intensity increases at the near-Earth duskside during disturbed geomagnetic conditions, enhanced SW Pdyn, and southward IMF, implying there location of effective inductive acceleration mechanisms and a strong duskward drift due to the increase of the magnetic field gradient in the near-Earth tail. Higher losses of energetic ions are observed in the dayside plasma sheet under disturbed geomagnetic conditions and enhanced SW Pdyn. These observations are in agreement with theoretical models.

We investigate the response of quasi-adiabatic particles to dynamical reconfigurations of the magnetotail field lines. Although they travel through a sharp field reversal with a characteristic length scale smaller than their Larmor radii, these quasi-adiabatic particles experience a negligible net change in magnetic moment. We examine the robustness of such a quasi-adiabatic behavior in the presence of a large surging electric field induced by magnetic field line reconfiguration as observed during the expansion phase of substorms. We demonstrate that, although such a short-lived electric field can lead to substantial nonadiabatic heating, quasi-adiabaticity is conserved for particles with velocities larger than the peak ExB drift speed. Because of the time-varying character of the magnetic field, it is not possible to use the adiabaticity parameter κ in a straightforward manner to characterize the particle behavior. We rather consider a κ parameter that is averaged over equatorial crossings. We demonstrate that particles intercepting the field reversal in the early stage of the magnetic transition may experience significant energization and enhanced oscillating motion in the direction normal to the midplane. In contrast, particles interacting with the field reversal in the late stage of the magnetic transition experience weaker energization and slower oscillations about the midplane. We show that quasi-adiabatic particles accelerated during such events can lead to energy–time dispersion signatures at low altitudes as is observed in the plasma sheet boundary layer.

Dominique Delcourt : Present address : Director LPC2E UMR 7328 CNRS Orléans France; International audience; We conducted global magnetohydrodynamics (MHD) simulation of Mercury's magnetosphere with the dipole offset, which was revealed by MESSENGER observations, in order to investigate its global structure under northward interplanetary magnetic field (IMF) conditions. Sodium ion dynamics originating from the Mercury's exosphere is also investigated based on statistical trajectory tracing in the electric and magnetic fields obtained from the MHD simulations. The results reveal a north-south asymmetry characterized by open field lines around southern polar region, and northward deflection of the plasma sheet in the far tail. The asymmetry of magnetic field structure near the planet drastically affects trajectories of sodium ion, and thus, their pressure distributions and precipitation pattern onto the planet. Weaker magnetic field strength in the southern hemisphere than in the north increases ion loss by precipitation onto the planetary surface in the southern hemisphere. The ‘sodium ring', which is formed by high-energy sodium ions drifting around the planet, is also found in the vicinity of the planet. The 'sodium ring' is almost circular under nominal solar wind conditions. The ring becomes partial under high solar wind density, because dayside magnetosphere is so compressed that there is no space for the sodium ions to drift around. In both cases, the 'sodium ring' is formed by sodium ions that are picked up and accelerated in the magnetosheath just outside the magnetopause and reentered into the magnetosphere due to combined effects of finite Larmor radius and convection electric field in the dawn-side magnetosphere.

Multiple energy dispersion structures of H+ ions that were observed at the passage of the INTERBALL-Auroral satellite through the plasma sheet at a geocentric distance of about 3R E, where R E is the radius of the Earth, on November 3, 1996, have been analyzed. The structure in the plasma sheet boundary layer, which has direct dispersion in energy and invariant latitude, in the range of 0.5–10.0 keV (velocity-dispersed ion structure) is an “autograph” of accelerated ion beams (primary beamlets) generated in the current sheet along the geomagnetic tail. The central plasma sheet contains five dispersion structures c1–c5 with the average energy ranging from 2.80 to 7.36 keV. The average energy of the structures increases with a decrease in the latitude. The event under consideration is a case of the regime of formation of the central plasma sheet by echo beamlets of the accelerated ion beam in the absence of a diffusion thermalized population of ions. This phenomenon is possibly explained by the fact that a magnetically quite period was observed three days before the passage of the satellite, when the regime of long-term diffusion of particles from the central plasma sheet occurred.

This work is devoted to the investigation of particle acceleration during magnetospheric dipolarizations. A numerical model is presented taking into account the four scenarios of plasma acceleration that can be realized: (A) total dipolarization with characteristic time scales of ≈3 min; (B) single peak value of the normal magnetic component B z occurring on the time scale of less than 1 min; (C) a sequence of rapid jumps of B z interpreted as the passage of a chain of multiple dipolarization fronts (DFs); and (D) the simultaneous action of mechanism (C) followed by the consequent enhancement of electric and magnetic fluctuations with the small characteristic time scale ≤1 s. In a frame of the model, we have obtained and analyzed the energy spectra of four plasma populations: electrons e−, protons H+, helium He+, and oxygen O+ ions, accelerated by the above-mentioned processes (A)–(D). It is shown that O+ ions can be accelerated mainly due to the mechanism (A); H+ and He+ ions (and to some extent electrons) can be more effectively accelerated due to the mechanism (C) than the single dipolarization (B). It is found that high-frequency electric and magnetic fluctuations accompanying multiple DFs (D) can strongly accelerate electrons e− and really weakly influence other populations of plasma. The results of modeling demonstrated clearly the distinguishable spatial and temporal resonance character of particle acceleration processes. The maximum particle energies depending on the scale of the magnetic acceleration region and the value of the magnetic field are estimated. The shapes of energy spectra are discussed.This work is devoted to the investigation of particle acceleration during magnetospheric dipolarizations. A numerical model is presented taking into account the four scenarios of plasma acceleration that can be realized: (A) total dipolarization with characteristic time scales of ≈3 min; (B) single peak value of the normal magnetic component B z occurring on the time scale of less than 1 min; (C) a sequence of rapid jumps of B z interpreted as the passage of a chain of multiple dipolarization fronts (DFs); and (D) the simultaneous action of mechanism (C) followed by the consequent enhancement of electric and magnetic fluctuations with the small characteristic time scale ≤1 s. In a frame of the model, we have obtained and analyzed the energy spectra of four plasma populations: electrons e−, protons H+, helium He+, and oxygen O+ ions, accelerated by the above-mentioned processes (A)–(D). It is shown that O+ ions can be accelerated mainly due to the mechanism (A); H+ and He+ ions (and to some exten...

[1] The interplanetary magnetic field (IMF) embedded in the solar wind interacts with the Martian crustal magnetic field and atmosphere. The IMF orientation is one of the important parameters to control the acceleration and precipitation of planetary heavy ions (PHIs). We statistically investigate the effects of the IMF orientation on PHI precipitations toward the ionosphere based on observations by Mars Express (MEX). We identified 59 PHI precipitation events between July 2007 and September 2009. To estimate the IMF orientation without magnetometer that MEX does not carry, we used the velocity distribution of exospheric-origin pickup protons. We estimated the IMF orientation without its polarity for 10 events. The results show that the precipitations of PHIs tend to be observed around pole regions in the MSE (Mars-centered, solar electrical) coordinates determined from the solar wind electric field (Esw), in which the pole axis directs to the parallel or antiparallel to Esw due to the ambiguity in the IMF polarity determination. The observed precipitating PHIs are accelerated only up to a few keV. This feature may reflect the short distance from the picked-up region. For one of these 10 events, we estimated the IMF polarity by comparing the velocity distribution of exospheric-origin pickup protons observed by MEX with those obtained from statistical trajectory tracing simulations under two cases of possible IMF polarity conditions. The estimated polarity indicates that the PHI precipitation in this event is observed in the downward electric field hemisphere in MSE, where Esw points to Mars in the pole region.

[1] We developed a self-consistent kinetic model of thin current sheets (TCS), taking into account the inhomogeneity of TCS parameters in the antisunward direction. We show that the charged particle dynamics depending on the magnetic field distribution in the downtail direction completely determines the magnetotail equilibrium structure. We demonstrate that transient ions as well as electrons are the main current carriers in this system, but the first ones support mostly the background (1-D) structure of the current sheet. The influence of electrons and quasi-trapped ions is found to vary depending upon downtail distance along the sheet. Assuming the conservation of the so-called quasi-adiabatic invariant, we show that quasi-trapped particles are distributed along the current sheet in such a way that they concentrate in the region with large values of normal magnetic field component. As a result quasi-trapped ions can dominate near the earthward edge of TCS. In contrast, the electron current becomes stronger in the TCS tailward region where the normal magnetic field component becomes weaker, and field line curvature drifts are enhanced. Our quasi-adiabatic model predicts that thin current sheets in the Earth's magnetotail should have weakly 2-D configuration which, similar to its 1-D analog considered earlier, conserves the multiscale “matreshka” structure with multiple embedded layers.

[1] To examine the effects of planetary surface conductivity and the southward interplanetary magnetic field (IMF) strength on ion dynamics, systematic trajectory tracings of Na+ ions were performed in the electric and magnetic field configurations obtained from magnetohydrodynamics (MHD) simulations of the solar wind-Mercury interaction. Comparison with a previous study, which used an analytical model that rescaled the Earth's magnetosphere and assumed the existence of the distant neutral line (DNL) in Mercury's magnetotail, shows a drastic change in the Na+ precipitation pattern due to the formation of the near-Mercury neutral line (NMNL) in MHD simulations. The Na+ precipitation band at approximately 30° of latitude (LAT), which was obtained in the previous study, disappeared in the equivalent low-conductivity MHD case due to the NMNL formation, while the NMNL formation causes high-energy Na+ precipitation in the equatorial region. The change in strength of the southward IMF (sBz) alters the location of the NMNL and the Na+ precipitation pattern. In the low-conductivity sBz = 5 case, both the equatorial precipitation and the Na+ band at approximately LAT = 30 are formed. In the high-conductivity sBz = 5 case, magnetospheric convection through the polar regions is suppressed, which results in a region of dense Na+ near the planet. These results suggest that the precipitation pattern of planetary ions onto Mercury's surface changes significantly with the activity level of Mercury's magnetosphere. It is also suggested that observations of the magnetospheric convection, the distribution of Na+ ions around the planet, or the precipitation pattern of Na+ ions onto the planetary surface can provide us information about the surface conductivity.

[1] Geomagnetic storms are frequently associated with the formation of multiple bands of energetic electrons inside the inner radiation belt at L = 1.1–1.9 and with prominent energy structures of protons inside the slot region at L = 2.2–3.5. These structures typically from 100 keV up to the MeV range result from coherent interactions of energetic particles with quasi-monochromatic ultra-low frequency (ULF) waves. These waves are induced by magnetospheric changes due to the arrival of dense solar material and related nightside injections of particles from the outer magnetosphere that destabilize field lines in the inner magnetosphere down to L = 1.1. Using low-altitude data from the polar orbiting Demeter spacecraft, we perform case and statistical studies of these structures. We show that with such a spacecraft, these structures are best seen near the South Atlantic Anomaly because of lowering of the belt particle mirror point. As evidenced from ground measurements, energy bands are associated with quasi-sinusoidal ULF Pc5 and Pc4 waves with periods in the 1000 s range for L = 1.1–1.9 and in the 60 s range for L = 2.2–3.5. Numerical simulations of the coherent drift resonance of energetic particles with ultra-low frequency waves show how the particles are accelerated and how the observed structures build up.

This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed.

Because of the small planetary magnetic field as well as proximity to the Sun that leads to enhanced solar wind pressure as compared to Earth, the magnetosphere of Mercury is very dynamical and at times subjected to prominent compression. We investigate the dynamics of magnetospheric ions during such compression events. Using three-dimensional single-particle simulations, we show that the electric field induced by the time varying magnetic field can lead to significant ion energization, up to several hundreds of eVs or a few keVs. This energization occurs in a nonadiabatic manner, being characterized by large enhancements of the ion magnetic moment and bunching in gyration phase. It is obtained when the ion cyclotron period is comparable to the field variation time scale. This condition for nonadiabatic heating is realized in distinct regions of space for ions with different mass-to-charge ratios. During compression of Mercury's magnetosphere, heavy ions originating from the planetary exosphere may be subjected to such an abrupt energization, leading to loading of the magnetospheric lobes with energetic material.

Mercury’s environment is a complex system, resulting from the interaction between the solar wind, magnetosphere, exosphere and surface. A comprehensive description of its characteristics requires a detailed study of these four elements. This paper illustrates and discusses the key processes that are implicated in the strong coupling of the Hermean magnetosphere with the other elements. The magnetosphere of Mercury, frequently called “mini-magnetosphere”, when compared to that of Earth, plays a significant role in controlling the planet source and loss processes, by means of both particle and field interactions. We review the status of our knowledge, and give possible interpretations of the still-limited data set presently available.

We investigate the dynamics of magnetospheric ions during transient reconfigurations of Mercury's magnetotail. At Earth, numerous observations during similar events reveal a prominent energization (up to the hundreds of keV range) of heavy ions ( O + ) originating from the topside ionosphere. This energization likely results from a resonant nonadiabatic interaction with the electric field that is induced by dipolarization of the magnetic field lines, the time scale of this reconfiguration being comparable to the heavy ion cyclotron period. The question then arises whether such an energization may occur at Mercury. Using single-particle simulations in time-varying electric and magnetic fields, we show that prominent nonadiabatic heating is obtained for ions with small mass-to-charge ratios (e.g., H + , He + ). As for heavy ions (e.g., Na + , Ca + ) that have cyclotron periods well above the time scale of the magnetotail reconfiguration (several seconds), a weaker energization is obtained. The resonant heating mechanism that we examine here may be of importance for solar wind protons that gain access to the inner hermean magnetotail as well as for light ions of planetary origin that directly feed the near-Mercury plasma sheet.

Using hybrid simulations, we examine how particles can diffuse across the Earth's magnetopause because of finite Larmor radius effects. We focus on tangential discontinuities and consider a reversal of the magnetic field that closely models the magnetopause under southward interplanetary magnetic field. When the Larmor radius is on the order of the field reversal thickness, we show that particles can cross the discontinuity. We also show that with a realistic initial shear flow, a Kelvin-Helmholtz instability develops that increases the efficiency of the crossing process. We investigate the distribution functions of the transmitted ions and demonstrate that they are structured according to a D-shape. It accordingly appears that magnetic reconnection at the magnetopause is not the only process that leads to such specific distribution functions. A simple analytical model that describes the built-up of these functions is proposed.

Also published in "Plasma Sources of Solar System Magnetospheres in 2016" edited by Andrew F. Nagy, Michel Blan, Charles R. Chappell and Norbert Krupp, Space Sciences Series of ISSI vol. 52, eISBN 978-1-4939-3544-4 (https://link.springer.com/chapter/10.1007/978-1-4939-3544-4_3) The aim of this paper is to provide a review of general processes related to plasma sources, their transport, energization, and losses in the planetary magnetospheres. We provide background information as well as the most up-to-date knowledge of the comparative studies of planetary magnetospheres, with a focus on the plasma supply to each region of the magnetospheres. This review also includes the basic equations and modeling methods commonly used to simulate the plasma sources of the planetary magnetospheres. In this paper, we will describe basic and common processes related to plasma supply to each region of the planetary magnetospheres in our solar system. First, we will describe source processes in Sect. 1. Then the transport and energization processes to supply those source plasmas to various regions of the magnetosphere are described in Sect. 2. Loss processes are also important to understand the plasma population in the magnetosphere and Sect. 3 is dedicated to the explanation of the loss processes. In Sect. 4, we also briefly summarize the basic equations and modeling methods with a focus on plasma supply processes for planetary magnetospheres.

International audience; Self-consistent kinetic (particle-in-cell) model of magnetotail thin current sheet (TCS) is used to understand the formation of self-consistent sheared magnetic structures. It is shown that shear configurations appear in TCS as a result of self-consistent evolution of some initial magnetic perturbation at the current sheet center. Two general shapes of shear TCS components are found as a function of the transverse coordinate: symmetric and antisymmetric. We show that TCS formation goes together with the emergence of field-aligned currents in the center of the current sheet, as a result of north-south asymmetry of quasi-adiabatic ion motions. Ion drift currents can also contribute to the magnetic shear evolution, but their role is much less significant, their contribution depending upon the normal component Bz and the amplitude of the initial perturbation in TCS. Parametric maps illustrating different types of TCS equilibria are presented that show a higher probability of formation of symmetric shear TCS configuration at lower values of the normal magnetic component.

International audience; This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed.

We investigate the non-linear dynamics of charged particles in the double-humped current sheets that develop in the Earth’s magnetotail. Using Poincare surfaces of section, we examine the various dynamical regimes that occur in a sharp field reversal and compare them to those obtained in single-humped current sheets. We demonstrate that bifurcation of the magnetotail current sheet does not alter the overall phase portrait structure which is characterized by three distinct regimes, viz., trapped, quasi-trapped, and transient. The phase portraits in single- and double-humped current sheets are not strictly identical though. A greater abundance of trapped particles and a distortion of the transient orbit domain are obtained in the latter case. In contrast, numerical simulations performed with an asymmetrical double-humped current distribution reveal considerable modification of the phase portrait with an expansion of the stochastic regime and a drastic reduction of the transient one. The degree of asymmetry in double-humped current sheets accordingly appears as a primary parameter to characterize the nonadiabatic behavior of charged particles.

In this study we discuss the proton circulation and the neutral atom emission at Mercury. The H+ distribution in space, energy and pitch angle has been simulated by means of a single-particle Monte Carlo model. The applied electric and magnetic field model has been parameterized to take into account different boundary conditions such as interplanetary magnetic field and cross-tail potential drop. Particular attention has been paid to the estimation of the surface-sputtered neutral atoms and the energetic neutral atoms generated via charge-exchange process. The peculiar configuration of the hermean magnetosphere, as it is expected after the Mariner-10 observation of a weak magnetic field, allows a significant part of the incoming solar wind to enter Mercury's environment. For the B z − 10 nT conditions, intense ion fluxes are expected in the cusp regions, which are extremely large when compared to the Earth's ones. The solar wind particles are likely to rapidly leave the hermean magnetosphere or precipitate onto the planetary surface, thus originating neutral particle emission via ion-sputtering. Two instruments, proposed to fly on board ESA mission BepiColombo (namely: the NPA-IS SERENA suite on the MPO segment and the ENA instrument on the MMO segment) will monitor the neutral signal as well as the precipitating ion particles. The modeled distribution presented here may be considered as a reference tool for the future observations.

We investigate the dynamics of charged particles in the dayside magnetosphere in response to abrupt variations of the solar wind dynamical pressure. Using test particle simulations, we show that the electric field induced by the compression of the frontside magnetosphere may be responsible for prominent energization of plasma sheet ions as well as trapping at high latitudes. We demonstrate that, due to the short-lived character of the magnetic field line reconfiguration (on the time scale of a few minutes), the particle magnetic moment (first adiabatic invariant) may not be conserved during such events. Ions that are initially bouncing from one hemisphere to the other are found to experience nonadiabatic energization up to the hundred of keV range while being injected into the outer cusp. Such injections involve particles from limited portions of the dayside flux tubes. The energetic particles that are produced in the outer cusp during such events subsequently circulate about the field minimum at high latitudes without intercepting the equatorial plane, thus contributing to the high-energy populations that are observed in this region of space.

Acceleration of charged particles is an essential ingredient of both magnetospheric substorms and geospace magnetic storms, and is a critical part of space weather. In the case of geospace storms, the ultimate result of particle acceleration is a bulk flow of electric charge through the inner magnetosphere, commonly known as the ring current. This paper is a critical review of the long-standing issue of the storm-substorm relationship, or, in other words, the capability or the necessity of substorms in the build-up of a storm-time ring current. We mainly address the physical effect itself, (e.g., the bulk acceleration of particles), and not the diagnostic of the process, (e.g., the Dst index), which has been the case very often. Within the framework of particle acceleration, substorms retain their storm-importance due to the acceleration potential of substorm-induced impulsive electric fields.

We examine the circulation of heavy ions of planetary origin within Mercury’s magnetosphere. Using single particle trajectory calculations, we focus on the dynamics of sodium ions, one of the main species that are ejected from the planet’s surface. The numerical simulations reveal a significant population in the near-Mercury environment in the nightside sector, with energetic (several keV) Na + densities that reach several tenths cm-3 at planetary perihelion. At aphelion, a lesser (by about one order of magnitude) density contribution is obtained, due to weaker photon flux and solar wind flux. The numerical simulations also display several features of interest that follow from the small spatial scales of Mercury’s magnetosphere. First, in contrast to the situation prevailing at Earth, ions in the magnetospheric lobes are found to be relatively energetic (a few hundreds of eV), despite the low-energy character of the exospheric source. This results from enhanced centrifugal acceleration during E × B transport over the polar cap. Second, the large Larmor radii in the mid-tail result in the loss of most Na + into the dusk flank at radial distances greater than a few planetary radii. Because gyroradii are comparable to, or larger than, the magnetic field variation length scale, the Na + motion is also found to be non-adiabatic throughout most of Mercury’s equatorial magnetosphere, leading to chaotic scattering into the loss cone or meandering (Speiser-type) motion in the near-tail. As a direct consequence, a localized region of energetic Na + precipitation develops at the planet’s surface. In this region which extends over a wide range of longitudes at mid-latitudes ( ~ 30°–40°), one may expect additional sputtering of planetary material.Key words. Magnetospheric physics (planetary magnetospheres) – Space plasma physics (charged particle motion and acceleration; numerical simulation studies)

This paper is devoted to the analysis of ion distributions in the velocity space {vx, vy} of the self-consistent thin current sheets (TCSs) due to the influence of nonadiabatic effects. In the frame of 1D-model it is shown that nonadiabatic jumps of the approximate integral of motion Iz may lead to the trapping of the particle in the vicinity of the sheet and influence significantly the structure of newly formed current sheets supported by ions at Speiser orbits. The part of the Speiser population is diffusing into the quasi-trapped domain, where ions have so called “cucumber” orbits. The scattering process results in the appearance of ions with large magnetic moments, which may reduce the current in the center of the sheet. We consider this process as deterioration, or “aging”, that might finally lead to TCS disruption. In the course of TCS “aging”, ion distribution functions experience characteristic evolution, which we are analyzing in this paper. The plots of velocity distribution functions corresponding to three characteristic moments of TCS “aging” are presented: 1) “young” sheet with only Speiser ions; 2) “deteriorated” TCS with the scattered quasi-trapped population; 3) “old” TCS before the very moment of destruction when the population of quasi-trapped plasma is very abundant. It is shown that quasi-trapped population occupies the well-defined domains in the phase space which could be identified by the in situ measurements of ion distribution function in the vicinity of the field reversal and may indicate the stage of the temporal TCS dynamical evolution.

We present an analysis of sporadic and recurrent injections of magnetospheric ions in the midnight auroral oval during substorms and of the associated ionospheric ion outflows. The source of plasma sheet precipitating ions is determined using a simple method, based on the measured relation between the ion inverse velocity and time ( l = v × t ). This method is applied here to two typical passes of the Interball-Auroral (IA) satellite at distances of ∼ 3 R E above the auroral regions. Substorm related ion injections are shown to be mainly due to time of flight effects. In contrast with particle trajectory computations (Sauvaud et al. , 1999), the inverse velocity method does not require magnetic and electric field models and can thus be used systematically for the detection of time of flight dispersed ion structures (TDIS). This allowed us to build a large database of TDIS events and to perform a statistical analysis of their spatial distribution. For the cases presented here the source region of the injected ions is found at radial distances from 18 to 30 R E near the equatorial magnetosphere. At Interball altitudes (∼ 3 R E ), ion injections detected at the poleward boundary of the nighside auroral oval are associated with shear Alfven waves superimposed over large-scale quasi-static current structures. We show that the most poleward TDIS are collocated with a large outflow of ionospheric H + and O + displaying pitch-angle distributions peaked in the pitch-angle range 90°–120°. These ions are thus accelerated perpendicularly to the magnetic field not only in the main auroral acceleration region but also up to at least 3 R E . The expanding auroral bulge thus constitutes a significant source of H + and O + ions for the mid-tail magnetosphere.

We review some features of charged particle dynamics during substorm dipolarization of the magnetic field lines in the inner magnetosphere. In the parallel direction, particles traveling at low latitudes are subjected to prominent equatorward-oriented acceleration due to the rapid direction-changing E × B drift. This centrifugal effect leads to focusing of ions with small parallel speeds into the equatorial region, which in turn yields the development of substantial (a few kV) parallel potential drops and the production of magnetic field-aligned electron beams. In the perpendicular direction, when the gyroperiod is comparable to the field-variation time scale, particles can experience abrupt nonadiabatic energization. As an example, O + ions originating from the ionosphere are accelerated up to hundreds of keV while being injected earthward, hence providing a seed population for the outer ring current. These results suggest that the electric field induced by relaxation of the magnetic field lines can play an active role in the dynamics of the inner magnetosphere during the main phase of geomagnetic storms.

Current sheets in the Earth's magnetosphere may be considered as the regions of the acceleration and heating of solar wind and ionospheric plasmas. We devote our attention to the formation of very thin current sheets (TCSs) in the magnetotail. Various models of TCS equilibrium are discussed. We extend our previous self-consistent analysis of TCS formation. We delineate the relative role of two types of ion populations: (1) current- carrying Speiser's ions, impinging from the mantle, (2) nonadiabatic ions resulting from chaotic scattering of ions on transient Speiser-type orbits. To take into account the effect of population (2) we use the centrifugal impulse model, which treats the scattering of the particle magnetic moments as the result of perturbation of the gyromotion by an impulsive centrifugal force. Using several “snapshots” of the scattered distribution function, we obtain a series of quasi-stationary TCS equilibria. It is shown that nonadiabatic effects do not influence significantly the TCS thickness but generally alter the structure of the “young” Speiser-orbit based current sheet, “polluting” the sheet by particles with large magnetic moments, which suppress the positive current in the center of the sheet. In other words, TCS are “aging” due to scattering. When the quasi-trapped population becomes too abundant, the equilibrium solutions decay. The characteristic lifetime of such TCS due to intrinsic nonadiabaticity of the system is found to be about 10–60 minutes.

In the auroral dawn and dusk magnetosphere at altitudes of ∼2-3 R E , three distinct zones of ion and electron precipitation are commonly detected onboard Interball 2, near the polar edge of the auroral oval. From high to low latitudes the satellite encounters (1) magnetosheath/low-latitude boundary layer (LLBL) like plasma (Zone 1), (2) a mixing region with plasma characteristics between LLBL and plasma sheet (Zone 2), and (3) the auroral plasma sheet precipitation (Zone 3). Further equatorward, the satellite crosses the inner plasma sheet characterized by ion gaps in the morning sector. Inside Zones 1 and 2 impulsive ion injections are often detected. They consist of overlapping energy dispersed structures from about 10 keV down to several hundreds of eV with temperature close to that of the magnetosheath. Using trajectory computations backward in time, these dispersions are shown to be cause by time-of-flight effect from a distant source located close to the equatorial magnetopause. Whereas Zone 1 is located mainly poleward of region 1 (downward field-aligned currents at dawn and upward field-aligned currents at dusk), Zone 2 generally coincides with region 1. It is mainly located on closed field lines, as evidenced from the local detection of bouncing ion clusters. Finally, Zone 3 corresponds with region 2 of upward field-aligned currents. A statistical study of Zone 1 which is present in about 12% of the satellite passes at dawn and dusk reveals that its probability of occurrence seems to be controlled by the interplanetary magnetic field (IMF). That is, it is formed when the IMF has a northward component and tends to be radially directed. Moreover, it is more frequently encountered during periods of enhanced solar wind pressure. Detailed case studies uncover a remarkable correlation between the onsets of individual injections inside Zone 1 and those of pressure pulses in the magnetosheath. Both have a characteristic period of ∼ 200- 250 s, similar to that of Pc5 events associated with these injections and detected on board Interball 2. Altogether, these observations indicate that injections and related Alfven waves are driven by magnetosheath pressure pulses associated with a quasi-parallel bow shock. The plasma penetration mechanism remains to be understood.

International audience; We investigate quasi-adiabatic dynamics of charged particles in strong current sheets (SCSs) in the solar wind, including the heliospheric current sheet (HCS), both theoretically and observationally. A self-consistent hybrid model of an SCS is developed in which ion dynamics is described at the quasi-adiabatic approximation, while the electrons are assumed to be magnetized, and their motion is described in the guiding center approximation. The model shows that the SCS profile is determined by the relative contribution of two currents: (i) the current supported by demagnetized protons that move along open quasi-adiabatic orbits, and (ii) the electron drift current. The simplest modeled SCS is found to be a multi-layered structure that consists of a thin current sheet embedded into a much thicker analog of a plasma sheet. This result is in good agreement with observations of SCSs at ˜1 au. The analysis of fine structure of different SCSs, including the HCS, shows that an SCS represents a narrow current layer (with a thickness of ˜104 km) embedded into a wider region of about 105 km, independently of the SCS origin. Therefore, multi-scale structuring is very likely an intrinsic feature of SCSs in the solar wind.

Reconfiguration of the magnetospheric current system during the expansion phase of substorms leads to dipolarization of the magnetic field lines in the inner plasma sheet. This process is characterized by inward field line motion in the equatorial region and outward motion at mid-latitudes. We investigate the parallel motion of ions during such dynamical reconfigurations. We demonstrate that, in contrast to equatorial latitudes where ions are centrifugally jetted toward the midplane and experience prominent energization, ions at mid-latitudes are subjected to a downward (earthward) oriented acceleration. We accordingly show that ions with small parallel speeds such as those originating from the topside ionosphere may be decelerated upon reaching mid-latitudes and return to low altitudes. Field line dipolarization during substorms may thus go together with substantial downward flow of low-energy ions, as evidenced from measurements of the low-altitude orbiting Interball-Auroral spacecraft.