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During the first flyby of the BepiColombo composite spacecraft at Mercury in October 2021 ion spectrometers observed two intense spectral lines with energies between 10 and 70 eV. The spectral lines persisted also at larger distances from Mercury and were observed again at lower intensity during cruise phase in March 2022 and at the second and third Mercury flyby as a single band. The ion composition indicates that water is the dominant gas source. The outgassing causes the composite spacecraft to charge up to a negative potential of up to −50 V. The distribution and intensity of the lower energy signal depends on the intensity of low energy electron fluxes around the spacecraft which again depend on the magnetic field orientation. We interpret the observation as being caused by water outgassing from different source locations on the spacecraft being ionized in two different regions of the surrounding potential. The interpretation is confirmed by two dimensional particle‐in‐cell simulations. The BepiColombo spacecraft is on its way through the inner solar system in a composite configuration consisting of two satellites and a propulsion unit with two large solar arrays. This configuration will only be separated after orbit insertion in December 2025. During the cruise phase and planetary flybys in the years 2021–2023 the ion spectrometers onboard the two satellites observed strong fluxes of low energy positive ions. We interpret these observations as being caused by outgassing of water from the spacecraft and a negative charging of the spacecraft caused by a high electron density surrounding the spacecraft. Around the first Mercury flyby in October 2021 all ion spectrometers observed two separate peaks in the low energy ion spectra. We explain these as being caused by water molecules being ionized by strong photon and electron fluxes in different regions of the negative potential surrounding the spacecraft. From these different potential regions ions are accelerated back to the spacecraft. Strong outgassing from the BepiColombo spacecraft was observed during first Mercury Flyby in 2021 and later during interplanetary cruiseThe gas composition is dominated by water moleculesThe ion energy spectra sometimes show a double band structure which we interpret as being caused by different ionization locations within a negative spacecraft potential Strong outgassing from the BepiColombo spacecraft was observed during first Mercury Flyby in 2021 and later during interplanetary cruise The gas composition is dominated by water molecules The ion energy spectra sometimes show a double band structure which we interpret as being caused by different ionization locations within a negative spacecraft potential

The Galileo spacecraft performed close flybys of the moon Callisto between 1996 and 2001. We reanalyzed particle data of the energetic particles detector onboard Galileo and derived pitch angle distributions in the energy range of several keV to MeV during Callisto flybys C3, C9, C10, and C30. We establish that field‐aligned beams observed during the flyby periods are more likely to originate from Callisto's magnetospheric interaction rather than by independent magnetospheric processes. These beams are prominent only during flyby C3, they come mainly from the North, and connect the moon and the ionosphere of Jupiter. For short intervals they have also been observed propagating from the South. The beams are regularly unidirectional and typically extend to 300 keV in energy, occasionally reaching above 600 keV. Energetic particle depletions in Callisto's wake during the downstream flybys are not at all obvious, even at low altitudes and in the wake center. The signature of the wake becomes more apparent when energetic particle observations are organized in pitch angle. In that case, pitch angle distribution minima at 90 deg can be discerned in some flybys, however, not always associated with a profound drop in the absolute signal intensity. They instead indicate that field‐aligned particle flux within the wake is higher. Outside the wake these minima continue in an energy‐dependent disturbed region toward Jupiter which seems to be at least partially collocated with Alfvén‐wing structures as predicted from magnetohydrodynamic simulation results or simple flyby geometry considerations. Pitch angle distributions of energetic electrons and ions during four close Callisto encounters of the Galileo spacecraft are analyzed and clear signatures of electron beams were found only for one of the four flybys. The beam energies extend up to 300 keV at least. The origin of those beams lies in the interaction between the plasma in the Jovian magnetosphere and the exosphere of Callisto. The electron beams were observed in regions of changing density and magnetic field values where the electrons are accelerated to maintain the current flow. The acceleration itself is most probably related to Alfvén waves. Pitch angle distributions of electrons are used to establish field‐aligned beams near Callisto from the moon‐magnetosphere interactionClose to the moons, field‐aligned electron are accelerated in regions with changing density and magnetic field to maintain the current flowThere is evidence that at Callisto Alfvén waves could have accelerated electrons along field lines up to several hundreds of keV Pitch angle distributions of electrons are used to establish field‐aligned beams near Callisto from the moon‐magnetosphere interaction Close to the moons, field‐aligned electron are accelerated in regions with changing density and magnetic field to maintain the current flow There is evidence that at Callisto Alfvén waves could have accelerated electrons along field lines up to several hundreds of keV

This study obtains a statistical representation of 2–15 keV heavy ions outside of the Martian‐induced magnetosphere and depicts their organization by the solar wind convective electric field (ESW). The overlap in the lifetime of Mars Global Surveyor (MGS) and Mars Express (MEX) provides a period of nearly three years during which magnetometer data from MGS can be used to estimate the direction of ESWin order to better interpret MEX ion data. In this paper we use MGS estimates of ESWto express MEX ion measurements in Mars‐Sun‐Electric field (MSE) coordinates. A new methodological technique used in this study is the limitation of the analysis to a particular instrument mode for which the overlap between proton contamination and plume observations is rare. This allows for confident energetic heavy ion identification outside the induced magnetosphere boundary. On the dayside, we observe high count rates of 2–15 keV heavy ions more frequently in the +ESWhemisphere (+ZMSE) than in the −ESWhemisphere, but on the nightside the reverse asymmetry was found. The results are consistent with planetary origin ions being picked up by the solar wind convective electric field. Though a field of view hole hinders quantification of plume fluxes and velocity space, this new energetic heavy ion identification technique means that Mars Express should prove useful in expanding the time period available to assess general plume loss variation with drivers. The location and flow direction of oxygen escaping Mars' atmosphere is organized by a global‐scale electric field associated with the Sun's flowing magnetic field. While the Mars Express (MEX) satellite is less well equipped than Mars Atmosphere and Volatile Evolution (MAVEN) to estimate exact flux values of ions accelerated by this electric field, our demonstration that MEX can see this population statistically opens a new window of time (pre‐MAVEN) to studies of the variability of this atmospheric escape channel. Mars Express heavy ion data outside the magnetic boundary show a statistical asymmetry consistent with other energetic plume studiesThe energetic plume is more prevalent on the dayside (i.e., X> 0), while for X< 0 higher count rates in the +ESWdirection were not seenFor a specific instrument setting, overlap between proton contamination and the plume is rare, allowing for confident plume identification

Since Mars lacks a global intrinsic magnetic field, the solar wind interacts directly with the Martian upper atmosphere and ionosphere. The presence of localized intense remnant crustal magnetic fields adds to this interaction, making the Martian plasma system a unique environment within the solar system. Rapid reductions in the electron flux, referred to as “electron holes,” occur within the Martian induced magnetosphere (IM). We present a statistical analysis of this phenomenon identified from proxy measurements of the electron flux derived from measurements by the Analyser of Space Plasmas and Energetic Neutral Atoms Electron Spectrometer experiment on board the Mars Express (MEX) spacecraft. The study is completed for the period of 9 February 2004 to 9 May 2014. Electron holes are observed within the IM in more than 56% of MEX orbits during this study period, occurring predominantly at altitudes less than 1300 km, with the majority in the negative X Mars‐Centric Solar Orbital direction. The spatial distribution above the surface of Mars is observed to bear close resemblance to that of the crustal magnetic fields as predicted by the Cain et al. [[Cain, J. C., 2003]] magnetic field model, suggesting that they play an important role in the formation of these phenomena. Extreme reductions in proxy measurements of electron flux observed by MEX within illuminated induced magnetosphereElectron holes distributed near or over regions of significant crustal magnetic field magnitudeAt higher altitudes more events occur over regions of larger model crustal magnetic field magnitude

Until now it is still questionable whether ions are accelerated to energies above 100 keV in the near‐Earth current sheet (CS), in the vicinity of a possible near‐Earth neutral line. By using 11 years of 3‐D energetic ion flux data for protons, helium, and oxygen (~150 keV–1 MeV) from the RAPID instrument on board Cluster 4, we statistically study the energetic ion acceleration by investigating ion anisotropies in the near‐Earth magnetotail (−20 RE< X<−16 RE). It is found that the earthward (tailward) anisotropy of the energetic (>150 keV) ions (protons, He+, and O+) tend to become higher as the earthward (tailward) plasma bulk flows (measured by Cluster Ion Spectrometry experiment) become stronger. During such periods the presence of a strong acceleration source tailward (earthward) of Cluster spacecraft (S/C) is confirmed by the hardening energy spectra of the earthward (tailward) energetic ion flows. A good statistical correlation between tailward bulk flow, negative Bz, and the tailward anisotropy of energetic ions indicates that the strong ion acceleration might be related to a near‐Earth reconnection, which occurred earthward of the Cluster S/C. The energetic ion anisotropies do not show a clear dependence on the AEindex, which may indicate that the acceleration source(s) for the energetic ions could be spatially localized. We present the observational evidence of ion acceleration in the plasma sheetThe acceleration of ions to energies > 150 keV may occur in the near‐Earth CSThe acceleration is a spatially localized process

Moraal and Steenberg (1999), showed that the peak energy in the anomalous cosmic ray spectra is independent of the radial distance up to a few AU away from the termination shock but dependent on the solar wind speed, the radius of the termination shock and the scattering strength. In this paper we will discuss the variation of the cosmic ray oxygen energy spectrum as measured by the UlyssesEPAC and the COSPIN/LET on board Ulysses. We found that the peak energy decreased from ∼5 MeV nucl−1, when Ulysseswas at high northern heliographic latitudes embedded in the fast solar wind to ∼3.5 MeV n−1, in the streamer belt. The shift towards lower energy might also be caused by changing modulation although Voyager measurements indicate no variation of the ACR Oxygen spectrum at ∼60 AU.

The plasma environment of Mars is highly influenced by its crustal magnetic fields. In this work, we investigate whether the crustal magnetic fields can be displaced from their original positions due to advection by ionospheric plasma flow. The ranges of interest are altitudes between 200and1000km and solar zenith angles between 45°and135°. We examine magnetic field data using measurements from the Magnetometer (MAG) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We conduct statistical analyses (∼5years of data) in order to investigate if horizontal shifts are observed between the data and the crustal magnetic field model by Langlais et al. (2019), https://doi.org/10.1029/2018je005854. We also show two case studies of individual measurements within a specific region of Mars. The results show statistical and observational evidence that the crustal magnetic fields are often being advected towards the night‐side of the planet. The displacement seems to increase exponentially as a function of altitude, reaching a horizontal shift of 100 km at 650 km altitude. Moreover, we use measurements from the SupraThermal And Thermal Ion Composition (STATIC) instrument in order to compare the dynamic pressure of ionospheric plasma flow to the magnetic pressure of the crustal magnetic fields. There are two possible causes for the displacement: a forcing by external magnetic pressure or an advection of the field to the electron fluid, which follows the ion fluid. In this paper, we argue that by the observed relation between ion fluid and displacement, the latter explanation is more probable. Crustal magnetic fields keep information of a past time, when Mars still had its own internal magnetic field generator. These structures do not tend to change in the long‐term, so several models have been built throughout the last decades with the aim of reproducing the observed Martian fields. The crustal fields can influence the dynamics of the atmosphere. The region of the atmosphere, which is dominated by atmospheric plasma (ions and electrons) is the ionosphere. At Mars, the ionosphere lies at ∼130km and above. In theory, the flow of the plasma is able to move the crustal magnetic fields in a process called advection. In this work, we indicate that this process happens often at Mars. Our results may be important for improving crustal magnetic field models, and also for estimating how much electricity the ionospheric plasma can conduct. The crustal magnetic fields on Mars are being displaced relative to their expected locationThe displacement increases with solar zenith angle and altitudeIonospheric plasma flow is most likely responsible for this process The crustal magnetic fields on Mars are being displaced relative to their expected location The displacement increases with solar zenith angle and altitude Ionospheric plasma flow is most likely responsible for this process

This report emphasizes new observational aspects of CIR ions revealed by advanced instruments launched on the Ulysses, WIND, SOHO, and ACE spacecraft, and by the unique vantage point of Ulysses which carried out the first survey of Corotating Interaction Region (CIR) properties over a very wide range of heliolatitudes. With this more complete observational picture established, this review is the basis to consider the status of theoretical models on origin, injection, and acceleration of CIR particles reported by Scholer, Mann et al.(1999) in this volume.

The relative abundances of low energy ions (0.6–2.0 MeV/n) in solar energetic particle (SEP) and corotating interaction region (CIR) events have been measured by the EPAC experiment aboard Ulysses since launch in October 1990 until the present time. We give an overview of the abundances of heavy ions (He, C, Ne, Fe) relative to oxygen during energetic particle events lasting longer than 5 days during the in- and out-of-ecliptic phase of the mission. While the period Oct. 1990 to Aug. 1992 was dominated by high solar activity the Ulysses out of ecliptic passage at solar latitudes up to 45° went parallel to the declining phase of solar activity. Thus a very clear structure of corotating interaction regions was observed. While the in-ecliptic composition is in general agreement with measurements made near the Earth, the development of the CIR-composition shows two phases: From Aug. 1992 to May 1993 the C/O-ratio is 0.55–0.70, afterwards it increases to 0.8–0.9. This increase is correlated to the disappearance of the current sheet at 30° solar latitude reported by Smithet al. (1993).

In November 1992, the Ulysses spacecraft observed a multiple solar particle event and a CME event at 5.2 AU and a heliographic latitude of 20° S which were superimposed to the recurrent corotating interacting region. Distinct particle flux increases caused by these events were observed in all energy channels of the EPAC experiment. The experimental findings are discussed.

Energetic particles, accelerated in shocks which were associated with recurrent fast solar wind streams, were observed in high heliographic latitudes; fifteen such steams were included in the present study. Intensity variations ranged up to four orders of magnitude. Energy spectra were typically steeper near forward shocks than near reverse shocks. Electrons were observed only lated to the reverse shocks. Composition ratios in accelerated streams resembled those observed in fast CIR's. In periods between the recurrent acceleration regions elemental abundance ratios were similar to those of the anomalous cosmic rays (ACR). The intensity of the accelerated particles declined as the latitude of ULYSSES increased, probably due to the weakening of the shocks.

The fluxes of anomalous oxygen (E ranging from 3.5-6.8 MeV/amu), as measured by the EPAC instrument on ULYSSES, show a recurrent variation with the solar rotation period, which is anticorrelated with the fluxes of particles accelerated at the shocks of a corotating interaction region (CIR), and correlated with the fluxes of galactic cosmic rays known to be modulated by the CIR. The amplitude of this variation is much higher than expected for galactic cosmic rays of the same rigidity.

The Martian bow shock distance has previously been shown to be anticorrelated with solar wind dynamic pressure but correlated with solar extreme ultraviolet (EUV) irradiance. Since both of these solar parameters reduce with the square of the distance from the Sun, and Mars' orbit about the Sun increases by ∼0.3 AU from perihelion to aphelion, it is not clear how the bow shock location will respond to variations in these solar parameters, if at all, throughout its orbit. In order to characterize such a response, we use more than 5 Martian years of Mars Express Analyser of Space Plasma and EneRgetic Atoms (ASPERA‐3) Electron Spectrometer measurements to automatically identify 11,861 bow shock crossings. We have discovered that the bow shock distance as a function of solar longitude has a minimum of 2.39RMaround aphelion and proceeds to a maximum of 2.65RMaround perihelion, presenting an overall variation of ∼11% throughout the Martian orbit. We have verified previous findings that the bow shock in southern hemisphere is on average located farther away from Mars than in the northern hemisphere. However, this hemispherical asymmetry is small (total distance variation of ∼2.4%), and the same annual variations occur irrespective of the hemisphere. We have identified that the bow shock location is more sensitive to variations in the solar EUV irradiance than to solar wind dynamic pressure variations. We have proposed possible interaction mechanisms between the solar EUV flux and Martian plasma environment that could explain this annual variation in bow shock location. Automatically identified bow shock crossings by Mars Express over 5 Martian years of dataThe bow shock distance at the terminator increases by 11% from near aphelion to near perihelionFunctional forms produced for bow shock response to solar EUV and dynamic pressure

We study the effect of the magnetosonic Mach number on the position of the bow shock (BS) at Mars. The magnetosonic Mach number is calculated from solar wind data obtained by the ACE satellite upstream of Earth and extrapolated to Mars during two intervals, starting in 2005 and 2007, when Mars and Earth were close to opposition. An increased Mach number is observed to cause the Martian BS to move to lower altitudes and the variation in the terminator altitude is proportional to the Mach number change. When the Mach number is lowered, the BS flares more. We also compare our results to previous studies at Venus. The variation in BS altitude with magnetosonic Mach number is found to be very similar to the variation of the Venusian BS, which has previously been shown to decrease linearly in altitude with increasing Mach number.