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In the Earth's magnetosphere wave‐particle interaction is a major ion energization process, playing an important role for the atmospheric escape. A common type of ion heating is associated with low‐frequency broadband electric wave fields. For such waves the energy is not concentrated to a certain narrow frequency range and exhibits no peaks or dips in a power spectrum. If there are enough fluctuations close to the ion gyrofrequency the electric field may still come in resonance with gyrating ions and heat them perpendicular to the background magnetic field. We perform a proof‐of‐concept study to investigate if this heating mechanism may contibute significantly to the energization of planetary ions also in the induced magnetosphere of Venus. We assume Alfvénic fluctuations and estimate the electric field spectral density based on magnetic field observations. We find typical estimated electric spectral densities of a few (mV/m)2${(\text{mV/m})}^{2}$/Hz close to Venus. This corresponds to a heating rate of a few eV/s. We consider an available interaction time of ∼${\sim} $300 s and conclude that this mechanism could increase the energy of an oxygen ion by about a keV. Observed thermal energies are in the range 100–1,000 eV and thus, resonant wave heating may also be important at Venus. Energization of O+escaping from Venus by Alfvén waves to keV energies is plausibleThe estimated electric power spectral density at the typical oxygen gyrofrequency is in the range 0.5–10 (mV/m)2/Hz close to the planetAn estimated heating rate of ≈3 eV/s is enough to explain oxygen thermal energies up to a keV Energization of O+escaping from Venus by Alfvén waves to keV energies is plausible The estimated electric power spectral density at the typical oxygen gyrofrequency is in the range 0.5–10 (mV/m)2/Hz close to the planet An estimated heating rate of ≈3 eV/s is enough to explain oxygen thermal energies up to a keV

At a low activity comet the plasma is distributed in an asymmetric way. The hybrid simulation code Amitis is used to look at the spatial evolution of ion velocity distribution functions (VDFs), from the upstream solar wind (SW) to within the comet magnetosphere where the SW is heavily mass‐loaded by the cometary plasma. We find that the spatial structures of the ions and fields form a highly asymmetric induced magnetosphere. The VDFs of SW and cometary ions vary drastically for different locations in the comet magnetosphere. The shape of the VDFs differ for different species. The SW protons show high anisotropies that occasionally resemble partial rings, in particular at small cometocentric distances. A second, decoupled, proton population is also found. Solar wind alpha particles show similar anisotropies, although less pronounced and at different spatial scales. The VDFs of cometary ions are mostly determined by the structure of the electric field. We perform supplementary dynamic particle backtracing to understand the flow patterns of SW ions that lead to these anisotropic distributions. This tracing is needed to understand the origin of cometary ions in a given part of the comet magnetosphere. The particle tracing also aids in interpreting observed VDFs and relating them to spatial features in the electric and magnetic fields of the comet environment. Hybrid simulations with the Amitis code for a low activity comet show the formation of an asymmetric induced magnetosphereThe velocity distributions of solar wind protons form partial rings in the simulation as previously reported by observationsBacktracing the cometary ions in the tail shows that the shape of their velocity distributions is driven by electric field structures Hybrid simulations with the Amitis code for a low activity comet show the formation of an asymmetric induced magnetosphere The velocity distributions of solar wind protons form partial rings in the simulation as previously reported by observations Backtracing the cometary ions in the tail shows that the shape of their velocity distributions is driven by electric field structures

We discuss a method to estimate the properties of a magnetospheric generator using a quasi‐electrostatic magnetosphere‐ionosphere coupling model and in situ or remote sensing observations of discrete quiet arcs. We first construct an ensemble of Vlasov equilibrium solutions for generator structures formed at magnetospheric plasma interfaces. For each generator solution, we compute the ionospheric electric potential from the current continuity equation. Thus, we estimate the field‐aligned potential drop that allows us to assess several properties of the discrete auroral arc, such as the field‐aligned potential difference, the field‐aligned current density, the flux of precipitating energy, and the height‐integrated Pedersen conductance. A minimization procedure based on comparing the numerical results with observations is defined and applied to find which solution of the current continuity equation and which generator model give auroral arc properties that best fit the observations. The procedure is validated in a case study with observations by DMSP and Cluster and can be generalized to other types of data. We discuss a method to estimate the properties of the auroral generator from low‐altitude observations of auroraThe method is based on a magnetosphere‐ionosphere quasi‐stationary coupling model, a parametric description of a magnetospheric interface generator, and a minimization procedure that finds the generator model whose auroral effects best fit in situ observationsThe method can be generalized to other types of generators and observables

We present a statistical study of magnetotail flows that change direction from earthward to tailward using Cluster spacecraft. More precisely, we study 318 events of particle flux enhancements in the O+data for which the pitch angle continuously changes with time, either from 0° to 180° or from 180° to 0°. These structures are called “Pitch Angle Slope Structures” (PASSes). PASSes for which the pitch angle changes from 0° to 180° are observed in the Northern Hemisphere while those for which the pitch angle changes from 180° to 0° are observed in the Southern Hemisphere. These flux enhancements result in a reversal of the flow direction from earthward to tailward regardless of the hemisphere where they are observed. Sometimes, several PASSes can be observed consecutively which can therefore result in oscillatory velocity signatures in the earth‐tail direction. The PASS occurrence rate increases from 1.8% to 3.7% as the AE index increases from ∼0 to ∼600 nT. Also, simultaneously to PASSes, there is typically a decrease in the magnetic field magnitude due to a decrease (increase) of the sunward component of the magnetic field in the Northern (Southern) Hemisphere. Finally, based on the 115 (out of 318) PASSes that show energy‐dispersed structures, the distance to the source from the spacecraft is estimated to be typically <25REalong the magnetic field line. This study is important as it sheds light on one of the causes of tailward velocities in Earth's magnetotail. Flow reversals from earthward to tailward can be due to an enhanced flux of earthward moving particles which move tailward after mirroringFlow reversals can be flux enhancements for which the pitch angle changes from 0° (180°) to 180° (0°) in the Northern (Southern) HemisphereThe particles forming the flow reversals have typically traveled <25REfrom the apparent source to the spacecraft

Here we present some unique observations of reconnection at a quasi‐perpendicular bow shock as an interplanetary directional discontinuity (DD) is crossing it simultaneously with the Magnetospheric Multiscale (MMS) mission. There are no burst data, but available data show indications of ongoing reconnection at the shock southward of MMS: a bifurcated current sheet with signatures of Hall magnetic and electric fields, normal magnetic fields indicating a magnetic connection between the two reconnecting regions, field‐aligned currents and electric fields, E·J>0 indicating a conversion of magnetic to kinetic energy, and subspin resolution ion energy‐time spectrograms indicating ions being accelerated away from the X‐line. The DD is also observed by four upstream spacecraft (ACE, WIND, Geotail, and ARTEMIS P1) and one downstream in the magnetosheath (Cluster 4), but none of them resolve signatures of ongoing reconnection. We therefore suggest that reconnection was temporarily triggered as the DD was compressed by the shock. Reconnection at the bow shock is inevitably asymmetric with both the density and magnetic field strength being higher on one side of the X‐line (magnetosheath side) than on the other side where the plasma flow also is supersonic (solar wind side). This is different from the asymmetry exhibited at the more commonly studied case of asymmetric reconnection at the magnetopause. Asymmetric reconnection of the bow shock type has never been studied before, and the data discussed here present some first indications of the properties of the reconnection region for this type of reconnection. First observations of externally driven reconnection in the bow shock ramp regionAsymmetric reconnection could be triggered as a current sheet is compressed at the bow shockNew type of asymmetry observed: high N and B on one side and supersonic V on other side of X‐line

Plasma dynamics in Earth's magnetotail is often studied using moments of the distribution function, which results in losing information on the kinetic properties of the plasma. To better understand oscillatory flows observed in the midtail plasma sheet, we investigate two events, one in each hemisphere, in the transition region between the central plasma sheet and the lobes using the 2‐D ion distribution function from the Cluster 4 spacecraft. In this case study, the oscillatory flows are a manifestation of repeated ion flux enhancements with pitch angle changing from 0° to 180° in the Northern Hemisphere and from 180° to 0° in the Southern Hemisphere. Similar pitch angle signatures are observed seven times in about 80 min for the Southern Hemisphere event and three times in about 80 min for the Northern Hemisphere event. The ion flux enhancements observed for both events are slightly shifted in time between different energy channels, indicating a possible time‐of‐flight effect from which we estimate that the source of particle is located ∼5–25REand ∼40–107REtailward of the spacecraft for the Southern and Northern Hemisphere event, respectively. Using a test particle simulation, we obtain ∼21–46 REfor the Southern Hemisphere event and tailward of X∼ − 65RE(outside the validity region of the model) for the Northern Hemisphere event. We discuss possible sources that could cause the enhancements of ion flux. Oscillatory flows can be due to repeated particle flux enhancements with clear pitch angle patternsThe pitch angle of the flux enhancements changes from 0 to 180 degrees in the Northern Hemisphere and from 180 to 0 degrees in the Southern HemisphereThe particles associated with the flux enhancements originate from a source tailward of the spacecraft

The European Space Agency/Rosetta mission to comet 67P/Churyumov‐Gerasimenko has provided several hundred observations of the cometary diamagnetic cavity induced by the interaction between outgassed cometary particles, cometary ions, and the solar wind magnetic field. Here we present the first electric field measurements of four preperihelion and postperihelion cavity crossings on 28 May 2015 and 17 February 2016, using the dual‐probe electric field mode of the Langmuir probe (LAP) instrument of the Rosetta Plasma Consortium. We find that on large scales, variations in the electric field fluctuations capture the cavity and boundary regions observed in the already well‐studied magnetic field, suggesting the electric field mode of the LAP instrument as a reliable tool to image cavity crossings. In addition, the LAP electric field mode unravels for the first time extremely low‐frequency waves within two cavities. These low‐frequency electrostatic waves are likely triggered by lower‐hybrid waves observed in the surrounding magnetized plasma. As sunlight heats a comet nucleus, frozen volatile gases sublimate are ionized and interact with the solar wind and its embedded magnetic field, inducing a dynamical plasma environment around the comet. With the cornerstone European mission Rosetta and its 2 years of near‐continuous orbiting of comet 67P/Churyumov‐Gerasimenko, the origin, structure, and evolution of this environment are only starting to be unveiled. Exciting are the numerous crossings of the diamagnetic cavity, the innermost plasma region from which the solar wind magnetic field is excluded. Whilst the magnetic field structure of the cavity crossings is well studied, the related electric field activity remains until now unexplored. Studying the electric field with the Langmuir probes onboard Rosetta, we find that whereas the large‐scale electric field structure agrees well with the observed magnetic field behavior during cavity crossings, unexpected short‐lived low‐frequency electric field signals manifest themselves within the cavity. We interpret these as electrostatic waves triggered by a modulating of the cavity boundary caused by observed electrostatic waves at the same frequency in the surrounding magnetized plasma. This unravels a new aspect of the electromagnetic activity in the inner cometary environment, which is crucial for our understanding of the comet‐solar wind‐induced plasma environment. The first continuous low‐frequency electric field observations of the diamagnetic cavity of comet 67P/Churyumov-Gerasimenko is here presentedObserved low‐frequency wave activity in the 3‐ to 8‐Hz range is interpreted as ion acoustic waves excitation due to a cavity boundary forcingThe magnetic and electric fields have similar characteristics while crossing the cavity

Spatio‐temporal variations of ionospheric currents cause rapid magnetic field variations at ground level and Geomagnetically Induced Currents (GICs) that can be harmful for human infrastructure. The risk for large excursions in the magnetic field time derivative, “dB/dtspikes”, is known to be high during geomagnetic storms and substorms. However, less is known about the occurrence of spikes during non‐stormy times. We use data from ground‐based globally covering magnetometers (SuperMAG database) from the years 1985–2021. We investigate the spike occurrence (|dB/dt| > 100 nT/min) as a function of magnetic local time (MLT), magnetic latitude (Mlat), and the solar cycle phases during non‐stormy times (−15 nT ≤ SYM‐H < 0). We sort our data into substorm (AL < 200 nT) intervals (“SUB”) and less active intervals between consecutive substorms (“nonSUB”). We find that spikes commonly occur in both SUBs and nonSUBs during non‐stormy times (3–23 spikes/day), covering 18–12 MLT and 65°–80° Mlat. This also implies a risk for infrastructure damage during non‐stormy times, especially when several spikes occur nearby in space and time, possibly causing infrastructure weathering. We find that spikes are more common in the declining phase of the solar cycle, and that the occurrence of SUB spikes propagates from one midnight to one morning hotspot with ∼10 min in MLT for each minute in universal time (UTC). Finally, we discuss causes for the spikes in terms of spatio‐temporal variations of ionospheric currents. Our active sun disturbs Earth's magnetosphere and causes current systems and space weather effects. For example, space weather driven currents in the upper ionized atmosphere (ionosphere) can cause large excursions (“spikes”) in the magnetic field time derivative at the ground level, dB/dt. These in turn cause Geomagnetically Induced Currents (GICs) in the ground and in human infrastructure, potentially causing burnouts in powerlines and transformers. It is well‐known that dB/dtspikes are common during geomagnetically active time such as geomagnetic storms and geomagnetic substorms. However, much less is known about the spike occurrence during non‐stormy times. In this article we show that spikes also occur often during non‐stormy times. Spikes are most common in the declining phase of the 11‐year solar cycle. Moreover, we show that the spike occurrence propagate with time: in the beginning of a substorm, spikes typically occur in the pre‐midnight magnetic local time sector, but later in the substorm, the spike occurrence has propagated to the morning sector. Our results imply that human infrastructure is not safe even during non‐stormy times. Instead, it can be exposed to harmful weathering also during those times. Potentially harmful dB/dt spikes are also common during non‐stormy times, for example, during weak SYM‐H and after substormsThe highest spike occurrence rate is in the declining phase of the solar cycleSubstorm spike occurrence exhibits propagation from midnight to morning sector: about 10 min propagation in MLT for each min in UT Potentially harmful dB/dt spikes are also common during non‐stormy times, for example, during weak SYM‐H and after substorms The highest spike occurrence rate is in the declining phase of the solar cycle Substorm spike occurrence exhibits propagation from midnight to morning sector: about 10 min propagation in MLT for each min in UT

No spacecraft visiting a comet has been equipped with instruments to directly measure the static electric field. However, the electric field can occasionally be estimated indirectly by observing its effects on the ion velocity distribution. We present such observations made by the Rosetta spacecraft on 19 April 2016, 35 km from the nucleus. At this time comet 67P was at a low outgassing rate and the plasma environment was relatively stable. The ion velocity distributions show the cometary ions on the first half of their gyration. We estimate the bulk drift velocity and the gyration speed from the distributions. By using the local measured magnetic field and assuming an E× Bdrift of the gyrocentre, we get an estimate for the average electric field driving this ion motion. We analyze a period of 13 hr, during which the plasma environment does not change drastically. We find that the average strength of the perpendicular electric field component is 0.21 mV/m. The direction of the electric field is mostly anti‐sunward. This is in agreement with previous results based on different methods. Measuring the static electric field in space plasmas is difficult. Most spacecraft do not have dedicated instruments for it, and the Rosetta mission to comet 67P is no exception. But the electric field is one of the main governing factors behind the motion of newly born cometary ions. In this study, we use measurements of the cometary ions to estimate the average electric field close to the nucleus. The observations are made on the 19 April 2016 by the Ion Composition Analyzer, which measures the energy and travel direction of the different plasma species. The specific shape of the observed velocity distribution of cometary ions—a partial ring—indicates that the fields accelerating the observed cometary ions are relatively homogeneous. The spatial scale this applies to is approximately one gyroradius, which we estimated to be around 340 km. The resulting electric field is 0.21 mV/m, which is significantly smaller than the expected field in the upstream solar wind, far away from the nucleus. Rosetta observations show partial ring distributions of cometary ions at comet 67P close to the nucleusFrom the velocity distributions the plasma bulk velocity and gyration speed are determinedWe estimate the perpendicular electric field component from the bulk velocity and find a mostly anti‐sunward field of 0.21 mV/m Rosetta observations show partial ring distributions of cometary ions at comet 67P close to the nucleus From the velocity distributions the plasma bulk velocity and gyration speed are determined We estimate the perpendicular electric field component from the bulk velocity and find a mostly anti‐sunward field of 0.21 mV/m

We use data from the first two dayside seasons of the Magnetospheric Multiscale (MMS) mission to study current systems associated with quasi‐perpendicular bow shocks of generator type. We have analyzed 154 MMS bow shock crossings near the equatorial plane. We compute the current density during the crossings and conclude that the component perpendicular to the shock normal (J⊥) is consistent with a pileup of the interplanetary magnetic field (IMF) inside the magnetosheath. For predominantly southward IMF, we observe a component Jnparallel (antiparallel) to the normal for GSM Y> 0 (<0), and oppositely directed for northward IMF. This indicates current closure across the equatorial magnetosheath, and it is observed for IMF clock angles near 0∘and 180∘. To our knowledge, these are the first observational evidence for bow shock current closure across the magnetosheath. Since we observe no clear signatures of |J⊥| decreasing toward large |Y| we suggest that the main region of current closure is further tailward, outside MMS probing region. For IMF clock angles near 90∘, we find indications of the current system being tilted toward the north‐south direction, obtaining a significant Jzcomponent, and we suggest that the current closes off the equatorial plane at higher latitudes where the spacecraft are not probing. The observations are complicated for several reasons. For example, variations in the solar wind and the magnetospheric currents and loads affect the closure, and Jnis distributed over large regions, making it difficult to resolve inside the magnetosheath proper. These are the first observations of bow shock current closure across the magnetosheath and toward the magnetosphereFor large IMF |Bz|, there are indications of current closure in the equatorial planeFor large IMF |By|, the current system is tilted and closure may occur at higher latitudes

We investigate the lagged correlation between a selection of geomagnetic indices and solar wind parameters for a complete solar cycle, from 2000 to 2011. We first discuss the mathematical assumptions required for such a correlation analysis. The solar wind parameters and geomagnetic indices have inherent timescales that smooth the variations of the correlation coefficients with time lag. Furthermore, the solar wind structure associated with corotating interaction regions and coronal mass ejections, and the compression regions ahead of them, strongly impacts the lagged correlation analysis results. This work shows that such bias must be taken into account in a correct interpretation of correlations. We then evidence that the magnetospheric response time to solar wind parameters involves multiple timescales. The simultaneous and quick response of the PCand AEindices to solar wind dynamic pressure with a delay of ~5 min suggests that magnetospheric compression by solar wind can trigger substorm activity. We find that the PCand AEindices respond to interplanetary magnetic field (IMF) BZwith a response time of respectively ~20 and ~35 min. The response of the SYM‐Hindex takes longer (~80 min) and is less sharp, SYM‐Hbeing statistically significantly correlated to the IMF BZobserved up to more than ~10 h before. Our results suggest that the solar wind velocity's dominant impact on geomagnetic activity is caused by the compression regions at the interface of fast/slow solar wind regimes, which are very geo‐effective as they are associated with high solar wind pressure and strong interplanetary magnetic field. Data from one solar wind cycle are used to study the lagged (Pearson) correlation between solar wind parameters and geomagnetic indicesThe impact of solar wind structuring and magnetospheric inherent response time on the result is analyzedThe solar wind structuring at the interface between fast/slow solar wind has strong impact on the results of the lagged correlation analysis

Magnetosheath jets are localized dynamic pressure enhancements in the magnetosheath. We make use of the high time resolution burst mode data of the Magnetospheric Multiscale mission for an analysis of waves in plasmas associated with three magnetosheath jets. We find both electromagnetic and electrostatic waves over the frequency range from 0 to 4 kHz that can be probed by the instruments on board the MMS spacecraft. At high frequencies we find electrostatic solitary waves, electron acoustic waves, and whistler waves. Electron acoustic waves and whistler waves show the typical properties expected from theory assuming approximations of a homogeneous plasma and linearity. In addition, 0.2 Hz waves in the magnetic field, 1 Hz electromagnetic waves, and lower hybrid waves are observed. For these waves the approximation of a homogeneous plasma does not hold anymore and the observed waves show properties from several different basic wave modes. In addition, we investigate how the various types of waves are generated. We show evidence that, the 1 Hz waves are connected to gradients in the density and magnetic field. The whistler waves are generated by a butterfly‐shaped pitch‐angle distribution and the electron acoustic waves by a cold electron population. The lower hybrid waves are probably generated by currents at the boundary of the jets. As for the other waves we can only speculate about the generation mechanism due to limitations of the instruments. Studying waves in jets will help to address the microphysics in jets which can help to understand the evolution of jets better. There is a constant plasma flow from the sun, the solar wind. The Earth's magnetic field deflects the solar wind as it flows toward Earth. As the solar wind plasma approaches Earth it gets decelerated and heated at the bow shock. Earthward of the bow shock, the magnetosheath is located where the flow diverges around Earth. In the magnetosheath plasma flows that are denser and faster than normal can sometimes be observed, so called magnetosheath jets. We investigate waves in plasmas in these magnetosheath jets and how they are generated. Studying these waves will help to understand the interaction of magnetosheath jets with their environment. MMS burst mode data is used to investigate waves in, and in the vicinity of, magnetosheath jets0.2 Hz waves, 1 Hz waves, whistler waves, electron acoustic waves, lower hybrid waves, and solitary waves are observedWaves with low frequencies cannot be explained by “basic” wave modes that are derived in homogeneous plasmas MMS burst mode data is used to investigate waves in, and in the vicinity of, magnetosheath jets 0.2 Hz waves, 1 Hz waves, whistler waves, electron acoustic waves, lower hybrid waves, and solitary waves are observed Waves with low frequencies cannot be explained by “basic” wave modes that are derived in homogeneous plasmas

We present partial ring distributions of solar wind protons observed by the Rosetta spacecraft at comet 67P/Churyumov‐Gerasimenko. The formation of ring distributions is usually associated with high activity comets, where the spatial scales are larger than multiple ion gyroradii. Our observations are made at a low‐activity comet at a heliocentric distance of 2.8 AU on 19 April 2016, and the partial rings occur at a spatial scale comparable to the ion gyroradius. We use a new visualization method to simultaneously show the angular distribution of median energy and differential flux. A fitting procedure extracts the bulk speed of the solar wind protons, separated into components parallel and perpendicular to the gyration plane, as well as the gyration velocity. The results are compared with models and put into context of the global comet environment. We find that the formation mechanism of these partial rings of solar wind protons is entirely different from the well‐known partial rings of cometary pickup ions at high‐activity comets. A density enhancement layer of solar wind protons around the comet is a focal point for proton trajectories originating from different regions of the upstream solar wind. If the spacecraft location coincides with this density enhancement layer, the different trajectories are observed as an energy‐angle dispersion and manifest as partial rings in velocity space. Particles of solar origin, called the “solar wind,” flow straight from the Sun in interplanetary space. When this solar wind meets an obstacle, such as a planet, it gets deflected around it. At comet 67P/Churyumov‐Gerasimenko, visited by the Rosetta spacecraft from 2014 to 2016, our instrument Rosetta Plasma Consortium (RPC)‐Ion Composition Analyzer (ICA) measured the main constituents of this solar wind: protons and alpha particles. When the comet is far away from the Sun, the solar wind protons are usually observed coming from the sunward direction with only slight deflection and constant velocities. On 19 April 2016, the main case for our study, we measure solar wind protons arriving in a wide range of directions. The velocity of these protons depends on how much they have been deflected. This creates partial ring distributions, which we visualize and quantify using a method specifically developed for this purpose. We show that these partial rings are a rare observation of a spatially confined region where solar wind protons from different regions of the solar wind are observed simultaneously. Broad energy spectra in our observations are due to solar wind protons forming partial ring distributionsThe partial ring distributions form due to solar wind proton trajectories focusing at a density enhancement layerFrom the partial ring distributions we estimate the average upstream magnetic field direction and the average bulk plasma drift velocity Broad energy spectra in our observations are due to solar wind protons forming partial ring distributions The partial ring distributions form due to solar wind proton trajectories focusing at a density enhancement layer From the partial ring distributions we estimate the average upstream magnetic field direction and the average bulk plasma drift velocity

In the first observation of Mars with XMM-Newton, on 20-21 November 2003, this planet is clearly detected as an X-ray source. High resolution X-ray spectroscopy with the Reflection Grating Spectrometer (RGS) confirms that the X-ray radiation from Mars is composed of two different components: one due to fluorescent scattering of solar X-rays in its upper atmosphere and the other one due to solar wind charge exchange in its exosphere. Close to Mars, the RGS spectrum is dominated by two pronounced CO2fluorescence lines at 23.5 Å and 23.7 Å. Fluorescence from N2at 31.5 Å is also observed. With increasing distance from Mars, these lines fade, while numerous (~12) emission lines become prominent at the positions expected for de-excitation of highly ionized C, N, O, and Ne atoms, strongly resembling a cometary X-ray spectrum. The He-like O6+multiplet is resolved and is dominated by the spin-forbidden magnetic dipole transition 2 $^3\rm S_1$$\to$1 $^1\rm S_0$, confirming charge exchange as the origin of the emission, while the resonance line 2 $^1\rm P_1$$\to$1 $^1\rm S_0$increases in intensity closer to Mars, where the density of the exosphere is higher. The high spectral dispersion and throughput of XMM-Newton / RGS make it possible to produce X-ray images of the Martian exosphere in individual emission lines, free from fluorescent radiation. They show extended emission out to ~8 Mars radii, with morphological differences between individual ions and ionization states. This is the first definite detection of charge exchange induced X-ray emission from the exosphere of another planet, providing a direct link to cometary X-ray emission.

We present a case study of inverse ion cyclotron damping taking place in the northern terrestrial magnetospheric cusp, exciting waves at the ion cyclotron frequency and its harmonics. The ion cyclotron waves are primarily seen as peaks in the magnetic‐field spectral densities. The corresponding peaks in the electric‐field spectral densities are not as profound, suggesting a background electric field noise or other processes of wave generation causing the electric spectral densities to smoothen out more compared to the magnetic counterpart. The required condition for inverse ion cyclotron damping is a velocity shear in the magnetic field‐aligned ion bulk flow, and this condition is often naturally met for magnetosheath influx in the northern magnetospheric cusp, just as in the presented case. We note that some ion cyclotron wave activity is present in a few similar shear events in the southern cusp, which indicates that other mechanisms generating ion cyclotron waves may also be present during such conditions. Inverse ion cyclotron damping is observed in the northern cuspThe waves are generated at the ion cyclotron frequencies and therefore effective in ion heatingThe mechanism may cause asymmetries between the Northern and Southern Hemispheres

The presence of a large‐scale planetary magnetic field is thought to be a protective factor for atmospheres, preventing them from being blown off by the solar wind. We focus on one key aspect of atmospheric escape: how does a planetary magnetic fields affect the energy transfer from the Sun to the atmosphere? We estimate the solar wind energy currently dissipated in the Earth's atmosphere using empirical formulas derived from observations. We show that it is significantly higher than the energy dissipated in the atmosphere of a hypothetical unmagnetized Earth. Consequently, we conclude that the Earth's magnetic field enhances the solar energy dissipation in the Earth's atmosphere and that, contrary to the old paradigm, an intrinsic magnetic field does not necessarily reduces atmospheric loss. The solar wind energy dissipated in the Earth's upper atmosphere is higher than it would be if the Earth were not magnetized The solar wind energy dissipated in the Earth's upper atmosphere is higher than it would be if the Earth were not magnetized

Observations of the green and red-doublet emission lines have previously been realized for several comets. We present here a chemistry-emission coupled model to study the production and loss mechanisms of the O(1S) and O(1D) states, which are responsible for the emission lines of interest for comet 67P/Churyumov-Gerasimenko. The recent discovery of O2in significant abundance relative to water 3.80 ± 0.85% within the coma of 67P has been taken into consideration for the first time in such models. We evaluate the effect of the presence of O2on the green to red-doublet emission intensity ratio, which is traditionally used to assess the CO2abundance within cometary atmospheres. Model simulations, solving the continuity equation with transport, show that not taking O2into account leads to an underestimation of the CO2abundance within 67P, with a relative error of about 25%. This strongly suggests that the green to red-doublet emission intensity ratio alone is not a proper tool for determining the CO2abundance, as previously suggested. Indeed, there is no compelling reason why O2would not be a common cometary volatile, making revision of earlier assessments regarding the CO2abundance in cometary atmospheres necessary. The large uncertainties of the CO2photodissociation cross section imply that more studies are required in order to better constrain the O(1S) and O(1D) production through this mechanism. Space weather phenomena, such as powerful solar flares, could be used as tools for doing so, providing additional information on a good estimation of the O2abundance within cometary atmospheres. The presence of O2within 67P's atmosphere increases significantly the red line emissionEstimations of CO2abundances based on the G/R ratio should be revised due to the O2presenceSpace weather phenomena such as solar flares have an impact on the comet photochemistry

Localized dynamic pressure pulses in the magnetosheath, or jets, have been a popular topic for discussion in recent decades. Studies show that they can propagate through the magnetosheath and impact the magnetopause, possibly showing up as geoeffective elements at ground level. However, questions still remain on how geoeffective they can be. Previous studies have been limited to case studies during few days and with only a handful of events. In this study we have found 65 cases of impacting jets using observations from the Multiscale Magnetospheric mission during 2015–2017. We examine their geoeffectiveness using ground‐based magnetometers (GMAGs). From our statistics we find that GMAGs observe responses as fluctuations in the geomagnetic field with amplitudes of 34 nT, frequencies of 1.9 mHz, and damping times of 370 s. Further, the parallel length and the maximum dynamic pressure of the jet dictate the amplitude of the observed GMAG response. Longer and higher pressure jets inducing larger amplitude responses in GMAG horizontal components. The median time required for the signal to be detected by GMAGs is 190 s. We also examine if jets can be harmful for human infrastructure and cannot exclude that such events could exist. Ground‐based magnetometers observe damped oscillations resulting from impacting jetsThe median damping time and observed frequency is 370 s and 1.9 mHz respectivelyWe suggest that larger and more energetic jets might increase the amplitude of the ground‐based magnetic response Ground‐based magnetometers observe damped oscillations resulting from impacting jets The median damping time and observed frequency is 370 s and 1.9 mHz respectively We suggest that larger and more energetic jets might increase the amplitude of the ground‐based magnetic response

The occurrence of tailward flows in the magnetotail plasma sheet is closely linked to the dynamics of earthward bursty bulk flows (BBFs). Tailward flows that are observed in the vicinity of these BBFs (or TWABs – Tailward flows around BBFs) may hold unique information on its origin. In this study, we conduct a statistical survey on TWABs by using data from the Cluster mission. We find that TWABs are observed in the vicinity of ∼75% of the BBFs and their occurrence does not depend on BBF velocity magnitude. TWABs have a flow convection pattern consistent with the general tailward flows (GTWs) in the plasma sheet and they do not resemble vortical‐like flows. However, TWABs have a flow velocity magnitude twice larger than the GTWs. The plasma density and temperature of TWABs are comparable with BBFs. It is more common to observe a TWAB succeeding than preceding a BBF. However, there is no distinctive difference (in flow pattern, plasma density and temperature) between preceding and succeeding TWABs. We suggest that TWABs are likely the “freshly” rebounded BBFs from the near‐Earth region where the magnetic field is stronger. TWABs may represent the early stage of the evolution of tailward flows in the plasma sheet. We also discuss and argue that other mechanisms such as shear‐induced vortical flows and tailward slipping of depleted flux tubes cannot be the principal causes of TWABs. In Earth's magnetotail, the plasma sheet is generally populated with slow earthward moving plasma. This plasma sheet is often perturbed by short bursts of earthward high speed flows, commonly known as the bursty bulk flows (BBFs). These BBFs are closely associated with the formation mechanisms of tailward flows in the magnetotail. The dynamic interaction between these tailward flows and BBFs can affect the energy, mass and momentum transport in the coupled magnetosphere‐ionosphere system. In this work, we conduct a statistical study on the tailward flows with a particular focus on those observed in the vicinity of BBFs (or TWABs, tailward flows around BBFs in short). We find that TWABs are common. They have a flow convection pattern consistent with, but a velocity magnitude twice larger than the general tailward flows in the plasma sheet. We also find that the plasma density and temperature of TWABs are comparable with BBFs. Based on their characteristics, we suggest that TWABs primarily result from the rebound of earthward flows in the near‐Earth region, where the magnetic field is stronger. Tailward flows around BBFs (TWABs) can frequently be observed. They have high |V| and plasma properties similar to bursty bulk flows (BBFs) compared to the general tailward flowsIt is more common to observe a TWAB succeeding than preceding a BBF. However, there is no distinctive difference between themTWABs are likely the “freshly” rebounded BBFs. They may represent the early stage of the evolution of tailward flows in the plasma sheet Tailward flows around BBFs (TWABs) can frequently be observed. They have high |V| and plasma properties similar to bursty bulk flows (BBFs) compared to the general tailward flows It is more common to observe a TWAB succeeding than preceding a BBF. However, there is no distinctive difference between them TWABs are likely the “freshly” rebounded BBFs. They may represent the early stage of the evolution of tailward flows in the plasma sheet

In Earth's magnetotail plasma sheet, the sunward‐tailward Bxcomponent of the magnetic field is often used to separate the region above and below the cross‐tail current sheet. Using a three‐dimensional magneto‐hydrodynamic simulation, we show that high‐speed flows do not only affect the north‐south magnetic field component (causing dipolarization fronts), but also the sunward‐tailward component via the formation of a magnetic dent. This dent is such that, in the Northern Hemisphere, the magnetic field is tailward while in the Southern Hemisphere, it is earthward. This is opposite to the expected signatures where Bx> 0 (Bx< 0) above (below) the neutral sheet. Therefore, the direction of the magnetic field cannot always be used to identify in which hemisphere an in situ spacecraft is located. In addition, the cross‐tail currents associated with the dent is different from the currents in a tail without a dent. From the simulation, we suggest that the observation of a dawnward current and a tailward magnetic tension force, possibly together with an increase in the plasma beta, may indicate the presence of a magnetic dent. To exemplify, we also present data of a high‐speed flow observed by the Cluster mission, and we show that the changing sign of Bxis likely due to such a dent, and not to the spacecraft moving across the neutral sheet. In the middle of the plasma sheet in the Earth's magnetotail exists an electrical current sheet that separates the magnetic field pointing away from (toward) Earth in the Southern (Northern) Hemisphere. This property of the magnetic field is usually used to identify the region of observation. However, by analyzing results from a three‐dimensional simulation and in situ observations, we show that this property of the magnetic field may not always hold. Indeed, in the presence of a fast earthward flowing plasma confined near the current sheet region, the magnetic field may instead be observed to point toward (away from) Earth in the Southern (Northern) Hemisphere, that is, opposite to the usual configuration. This is because the fast earthward flow deforms the magnetic field lines in such a way that the field lines wrap around the forefront of the fast earthward flow. This wrapping of the magnetic field lines results in a magnetic field orientation opposite to what is expected, namely, it is earthward in the Southern Hemisphere and tailward in the Northern Hemisphere. Simulation and Cluster data show dents in the magnetic field lines ahead of high‐speed flowsWithin a dent, Geocentric Solar Magnetospheric Bx> 0 (Bx< 0) is observed in the Southern (Northern) HemisphereThus, using the sign of the measured Bxto identify where a satellite is can lead to errors Simulation and Cluster data show dents in the magnetic field lines ahead of high‐speed flows Within a dent, Geocentric Solar Magnetospheric Bx> 0 (Bx< 0) is observed in the Southern (Northern) Hemisphere Thus, using the sign of the measured Bxto identify where a satellite is can lead to errors

Plasma structures with enhanced dynamic pressure, density, or speed are often observed in Earth's magnetosheath. We present a statistical study of these structures, known as jets and fast plasmoids, in the magnetosheath, downstream of both the quasi‐perpendicular and quasi‐parallel bow shocks. Using measurements from the four Magnetospheric Multiscale (MMS) spacecraft and OMNI solar wind data from 2015–2017, we present observations of jets during different upstream conditions and in the wide range of distances from the bow shock. Jets observed downstream of the quasi‐parallel bow shock are seen to propagate deeper and faster into the magnetosheath and on toward the magnetopause. We estimate the shape of the structures by treating the leading edge as a shock surface, and the result is that the jets are elongated in the direction of propagation but also that they expand more quickly in the perpendicular direction as they propagate through the magnetosheath. The solar wind is a stream of charged particles continuously emitted from the upper atmosphere of the Sun. When it approaches Earth, it is slowed down and creates the bow shock. The region with high temperature and lower speed, downstream of the bow shock is called the magnetosheath. From time to time, plasma jets with speeds close to the solar wind speed are observed in this magnetosheath. They are thought to be formed at the bow shock, which is the boundary between the magnetosheath and the solar wind. In this article, we use data obtained by the four MMS spacecraft, while they passed through the magnetosheath, in a statistical study of the properties of the jets. We have found that they slow down as they move through the magnetosheath and that, in the beginning, they are elongated in the direction of their motion, but also that they expand to become rounder as they move along. The jets grow larger and slower as they move away from the bow shockThe deceleration of jets and fast plasmoids in the quasi‐perpendicular magnetosheath is twice as fast as in the quasi‐parallel magnetosheathJets propagate deeper into the magnetosheath for smaller angles between the interplanetary magnetic field and the bow shock normal

A hybrid simulation of the solar wind‐Mars interaction and a test particle simulation of heavy ion trajectories near Mars are used to compute the contribution from solar wind charge exchange processes to the X‐ray emission from Mars. It is found that the X‐ray halo observed by the Chandra X‐ray observatory can be explained by emissions from heavy, highly charged, ions in the solar wind undergoing charge exchange collisions in the upper atmosphere of Mars.