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The correlation between space environment conditions and the properties of escaping ions is a central topic of Mars research. Although empirical correlations have been visible in the data, a physics-based interpretation, rather than statistics-based pictures, has not been established yet. As a first effort, we investigate the electric field, the direct contributor to ion acceleration, in the Mars plasma environment from a hybrid plasma model (particle ions and fluid electrons). We use Amitis, a hybrid model combined with an observation-based ionospheric model, to simulate the Mars–solar wind interaction under nominal solar wind plasma conditions for perpendicular and Parker spiral directions of the interplanetary magnetic field (IMF). The simulations show following results: (1) the electric field morphology is structured by the IMF direction and the different plasma domains in the solar wind–Mars interaction; (2) asymmetry of the electric field between the hemispheres where the convective electric field points inward and outward, respectively, due to the mass loading and asymmetric draping of the magnetic field lines; (3) the motional electric field dominates in most regions, especially in the dayside magnetosheath; and (4) the Hall term is an order of magnitude weaker and significant in the magnetotail and plasma boundaries for a perpendicular IMF case. The Hall term is relatively stronger for the Parker spiral case. (5) The ambipolar electric field, in principle, agrees with Mars Atmosphere and Volatile Evolution measurements in the magnetosheath.

In this series of papers, we present statistical maps of mirror-mode-like (MM) structures in the magnetosheaths of Mars and Venus and calculate the probability of detecting them in spacecraft data. We aim to study and compare them with the same tools and a similar payload at both planets. We consider their dependence on extreme ultraviolet (EUV) solar flux levels (high and low) and, specific to Mars, on Mars Year (MY) as well as atmospheric seasons (four solar longitudes Ls). We first use magnetic-field-only criteria to detect these structures and present ways to mitigate ambiguities in their nature. In line with many previous studies at Earth, this technique has the advantage of using one instrument (a magnetometer) with good time resolution, facilitating comparisons between planetary and cometary environments. Applied to the magnetometer data of the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft from November 2014 to February 2021 (MY32–MY35), we detect events closely resembling MMs lasting in total more than 170 000 s, corresponding to about 0.1 % of MAVEN's total time spent in the Martian plasma environment. We calculate MM-like occurrences normalised to the spacecraft's residence time during the course of the mission. Detection probabilities are about 1 % at most for any given controlling parameter. In general, MM-like structures appear in two main regions: one behind the shock and the other close to the induced magnetospheric boundary, as expected from theory. Detection probabilities are higher on average in low-solar-EUV conditions, whereas high-solar-EUV conditions see an increase in detections within the magnetospheric tail. We tentatively link the former tendency to two combining effects: the favouring of ion cyclotron waves the closer to perihelion due to plasma beta effects and, possibly, the non-gyrotropy of pickup ion distributions. This study is the first of two on the magnetosheaths of Mars and Venus.

In this series of papers, we present statistical maps of mirror mode-like (MM) structures in the magnetosheaths of Mars and Venus and calculate the probability of detecting them in spacecraft data. We aim to study and compare them with the same tools and a similar payload at both planets. We consider their dependence on Extreme Ultraviolet (EUV) solar flux levels (high and low), and, specific to Mars, on Mars Year (MY) as well as atmospheric seasons (four solar longitudes Ls). We first use magnetic field-only criteria to detect these structures and present ways to mitigate ambiguities in the nature of the detected structures. In line with many previous studies at Earth, this technique has the advantage of using one instrument (a magnetometer) with good time resolution facilitating comparisons between planetary and cometary environments. Applied to the magnetometer data of the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft from November 2014 to February 2020 (MY32–MY35), we detect structures closely resembling MMs lasting in total more than 170,000 s, corresponding to about 0.1 % of MAVEN's total time spent in the Martian plasma environment. We calculate MM-like occurrences normalised to the spacecraft's residence time during the course of the mission. Detection probabilities are about 1 % at most for any given controlling parameter. In general, MM-like structures appear in two main regions, one behind the shock, the other close to the induced magnetospheric boundary, as expected from theory. Detection probabilities are higher on average in low solar EUV conditions, whereas high solar EUV conditions see an increase in detections within the magnetospheric tail. We tentatively link the former tendency to two combining effects: the favouring of ion cyclotron waves the closer to perihelion due to plasma beta effects, and, possibly, the nongyrotropy of pickup ion distributions. This study is the first of two on the magnetosheaths of Mars and Venus.

Temperature anisotropy-driven instabilities such as the mirror mode and ion cyclotron instabilities are responsible for the generation of waves in the turbulent magnetosheath of planets. We present here a statistical study of mirror mode-like structures in the magnetosheath of Venus as observed by the Venus Express spacecraft. As in our Mars study (see poster by Simon Wedlund et al. in the same session), we use magnetic field-only measurements to constrain and identify these quasi-linear compressive structures and discuss ways to mitigate false positive detections based on one instrument only. After calculating the residence time of the spacecraft in the Venusian magnetoenvironment, we show two-dimensional statistical maps of mirror mode-like occurrence rates with respect to EUV solar flux levels, and type of bow shock (quasi-perpendicular vs quasi-parallel). We find detection probabilities of about 10% at most, with two main regions of occurrence, one behind the collisionless shock, the other close to the induced magnetospheric boundary, with the small modulation of the probability due to EUV solar flux conditions.

Out of the two Venus flybys that BepiColombo uses as a gravity assist manoeuvre to finally arrive at Mercury, the first took place on 15 October 2020. After passing the bow shock, the spacecraft travelled along the induced magnetotail, crossing it mainly in the YVSO direction. In this paper, the BepiColombo Mercury Planetary Orbiter Magnetometer (MPO-MAG) data are discussed, with support from three other plasma instruments: the Planetary Ion Camera (SERENA-PICAM) of the SERENA suite, the Mercury Electron Analyser (MEA), and the BepiColombo Radiation Monitor (BERM). Behind the bow shock crossing, the magnetic field showed a draping pattern consistent with field lines connected to the interplanetary magnetic field wrapping around the planet. This flyby showed a highly active magnetotail, with e.g. strong flapping motions at a period of ∼7 min. This activity was driven by solar wind conditions. Just before this flyby, Venus's induced magnetosphere was impacted by a stealth coronal mass ejection, of which the trailing side was still interacting with it during the flyby. This flyby is a unique opportunity to study the full length and structure of the induced magnetotail of Venus, indicating that the tail was most likely still present at about 48 Venus radii.

ESA's Mars Express (MEX) spacecraft has operated in Mars orbit since 2003. On-board MEX, the ASPERA-3 (Analyser of Space Plasma and EneRgetic Atoms) instrument is providing a unique dataset of the space plasma near Mars for more than 18 years, covering a complete solar cycle, allowing long-term inverstigation of the interaction of Mars with the solar wind.The large number of observations also enables unique statistical studies. Here we present two ASPERA-3 Ion Mass Analyzer (IMA) higher level data sets that will be available through the ESA's Planetary Science Archive (PSA): Solar wind ion moments and Ion differential flux.

While the orbital and environmental parameters (e.g. orbit-Sun-distance, planetary mass/diameter, rotation rate, surface pressure) of Venus and Mars are very different, their planetary ionospheres show many similarities. The photochemically dominated regions of the undisturbed dayside ionospheres of Venus (Figure 1) and Mars (Figure 2) contain two major features: The ionospheric main peak (V2 at Venus and M2 at Mars) both originate from photoionization by solar EUV radiation, while the weaker secondary V1/M1 region is based on the primary and secondary ionization by solar X-ray radiation [1]. The upper region of the Venus and Mars dayside ionospheres is dominated by transport processes. The extent and shape of these regions in Venus Express Radio Science (VEX-VeRa) and Mars Express Radio Science (MEX-MaRS) observations is highly variable on temporal scales and ranges from an undisturbed exponential decay (Figure 1a and 2a) to strongly compressed shapes (Figure 1b and 2b). In this work, 9 years of VEX-VeRa (2006-2014) and 18 years of MEX-MaRS (2004-ongoing) radio science observations are used to study the behavior of the upper ionospheric region of Venus and Mars. The identified parameters will be compared to other characteristics of the solar wind interaction region of both planets identified by Venus Express [2], Mars Express [3] and MAVEN [4] to improve our understanding of the solar wind interaction of planets without a global magnetic field. The effect of potential drivers on the temporal variability of the upper ionosphere are investigated for Venus and Mars by comparison with pristine solar wind parameters (e.g. VEX-ASPERA4 [5], MEX-ASPERA3 [6]) and solar radiation fluxes (FISM-V2 model [7], MAVEN EUV monitor [8]). References [1] Fox et al. (1996) Adv. Space Res., 17 (11). [2] Titov et al. (2006) Cosmic Research 44 (4). [3] Fletcher (2004) Mars Express. The scientific payload. ESA. [4] Jakosky B. M. et al. (2015) SSR, 195, 3-48. [5] Barabash et al. (2007) PSS, 55 (12). [6] Barabash et al. (2006) SSR, 126, 113-164. [7] Chamberlin et al. (2020) Space Weather, 18 (12). [8] Thiemann et al. (2017) JGR Space Phys., 122 (3).

Mercury does not possess an atmosphere. The magnetospheric plasma is thus interacting with the surface directly. The solar wind may directly access the surface when its dynamic pressure is high. The existence of the surface governs the plasma dynamics at Mercury. For example, the surface behaves as the sink of the space plasma (magnetospheric ions, electrons, and solar wind plasma). In addition, the surface is also the source of plasma (sputtered ions, reflected ions, photoelectrons) and neutral atoms (sputtered constituents, reflected atoms at various energies). The ongoing physics is a complex, interdisciplinary solar wind–magnetosphere–surface–exosphere coupling. The energetic neutral atom (ENA) imaging, a powerful diagnostic tool to image the plasma dynamics in a remote-sensing way, is highly suitable for characterizing the coupling. The surface is the source of ENAs via the sputtering and scattering (reflecting) processes. Therefore, the ENA measurements provide information on the plasma characteristics at the surface (at 0 km altitude) on a global scale, which is very difficult to obtain via in-situ plasma measurements. The information is highly unique by itself to characterize the plasma–surface interaction at Mercury. In addition, the ENA data includes information about physics operated on the precipitating ions between the spacecraft and the surface. This will allow complementary investigation of the plasma dynamics by combining with the in-situ plasma measurements. The other relevant source of ENAs is charge-exchange of energetic ions with the Mercury’s exosphere. The exosphere is tenuous, but still sufficiently dense to make charge-exchange collisions happen and then generate ENAs. Due to the small size of the Mercury’s magnetosphere, the dayside magnetosphere is easily filled with ions injected from the tail, which makes magnetosphere more variable than Earth’s. ENA images on the day side expect to visualize the shape of the magnetosphere. In this presentation, we will give a short review of sciences that ENA imaging at Mercury can address. The major science cases include: Precipitating ions at the surface. Imaging of open/close field regions: How much are the ions precipitating on the surface? What is the difference in flux, energy, and constituents between the open and close field lines? What are the temporal and spatial variations of ion precipitation? Physics below the spacecraft altitude. Measuring the potential drops between the spacecraft and the surface: What are the characteristic energies of ions at the surface? How much does the field-aligned potential exist? What are the temporal and spatial variations of the potential drop? Shape and variability of the magnetosphere: What is the shape of the dayside magnetosphere? How variable is the magnetosphere? During the cruise phase of BepiColombo, the field-of-view of the MPPE/ENA instrument is partially blocked by the MOSIF, the sunshield structure that will be discarded upon MPO and Mio separation, and a few side pixels are looking towards space. The instrument has been operated during the Earth, Venus and Mercury flybys as well as interplanetary cruising phase. We will present the instrument status as well as preliminary flight data taken during flybys.

In this series of papers, we present statistical maps of mirror mode-like (MM) structures in the magnetosheaths of Mars and Venus and calculate the probability of detecting them in spacecraft data. We aim to study and compare them with the same tools and a similar payload at both planets. We consider their dependence on Extreme Ultraviolet (EUV) solar flux levels (high and low). The detection of these structures is done through magnetic field-only criteria and ambiguous determinations are checked further. In line with many previous studies at Earth, this technique has the advantage of using one instrument (a magnetometer) with good time resolution facilitating comparisons between planetary and cometary environments. Applied to the magnetometer data of the Venus Express (VEX) spacecraft from May 2006 to November 2014, we detect structures closely resembling MMs lasting in total more than 93,000s, corresponding to about 0.6 % of VEX's total time spent in the Venus's plasma environment. We calculate MM-like occurrences normalised to the spacecraft's residence time during the course of the mission. Detection probabilities are about 10 % at most for any given controlling parameter. In general, MM-like structures appear in two main regions, one behind the shock, the other close to the induced magnetospheric boundary, as expected from theory. For solar maximum, the active region behind the bow shock is further inside the magneosheath, near the solar minimum bow shock location. The ratios of the observations during solar minimum and maximum are slightly dependent on the depth Δ B / B of the structures, deeper structures are more prevalent at solar maximum. A dependence on solar EUV (F10.7) flux is also present, where at higher F10.7 flux the events occur at higher values than the daily average value of the flux. Combining the plasma data from the Ion Mass Analyser with the magnetometer data shows that the instability criterion for MMs is reduced in the two main regions where the structures are measured, whereas it is still enhanced in the region in-between these two regions, implicating that the generation of MMs is transferring energy from the particles to the field. This study is the second of two on the magnetosheaths of Mars and Venus, and a third paper comparing the results obtained at the two planets will follow.

Using Mars Express data from 2007 until 2020 we show how ion outflow from Mars varied over more than a solar cycle, from one solar minimum to another. The data was divided into intervals with a length of one Martian year, starting from 30 April 2007 and ending 13 July 2020. The net escape rate was about 5 × 1 0 24 s − 1 in the first covered minimum, and 2 − 3 × 1 0 24 s − 1 in the most recent minimum. Ion escape peaked at 1 × 1 0 25 s − 1 during the intervening solar maximum. The outflow is a clear function of the solar cycle, in agreement with previous studies which found a clear relationship between solar EUV flux and ion escape at Mars. The outflow during solar maximum is 2.5 to 3 times higher than in the surrounding solar minima. The average solar wind dynamic pressure over a Martian year was investigated, but does not vary much with the solar cycle. The escape rate at solar maximum is in good agreement with some recent MAVEN studies, and dominated by low energy ions at most sampled locations. A simple linear fit to the data gives a prediction of the escape rate for the much stronger solar maximum during the Phobos mission in 1989 that is consistent with observations. The fit also implies a non-linear response of ion escape for low solar EUV, with a lower initial escape response for lower solar EUV levels than those of the studied data set.

As Venus does not have an intrinsic magnetic field, the solar wind interacts directly with the Venusian atmosphere, altering its structure and composition, for example through atmospheric ion escape to space. In particular, the interaction will result in the formation of plasma boundaries, which separate regions of different plasma populations around Venus. Knowing how space weather influences the shape of these boundaries is one of the key pieces to understanding the current state of the Venusian atmosphere.During its eight years mission, including more than 3000 orbits around Venus, Venus Express made measurements of the plasma environment, covering a wide range of upstream conditions. Using conjoint plasma and magnetic field measurements from the ASPERA-4 (Analyser of Space Plasma and Energetic Atoms) and the magnetometer instruments, we identified the locations where the spacecraft crossed the bow shock and the ion composition boundary for each orbit. Using the derived dataset, we then determined the boundary shapes with a two-parameter fit. The boundary shape fittings were done with respect to one or multiple upstream conditions.Here we report that both boundaries are highly dependent on solar wind extreme ultraviolet (EUV) flux, expanding further from the planet at solar maximum. A likely explanation is that at solar maximum, combined heating of the exosphere ions and a higher photoionization rate lead to a higher planetary ion production. These additional ions increase the internal thermal pressure, pushing the boundaries outward.Additionally, at solar minimum, solar wind parameters like dynamic pressure and energy flux were found to not affect the shape of the bow shock, which is consistent with previous studies. The influence of the strength and orientation of the interplanetary magnetic field, the Mach number, and potential correlations between multiple upstream parameters, are also discussed in this talk.

The Venusian dayside ionosphere, similar to other planetary ionospheres, is produced primarily by ionization of its neutral upper atmosphere due to solar extreme ultraviolet (EUV) radiation. It has become clear that the expansion of the ionosphere may be strongly controlled by the EUV level, as exhibited in data collected by the Pioneer Venus Orbiter (PVO) during one solar cycle (1978–1992). However, the EUV-dependence of the Venusian dayside ionopause altitude, which defines the outer boundary of the ionosphere, remains obscure because the PVO crossed the dayside ionopause only during the solar maximum; its periapsis lifted too high during the solar minimum. Recently, during the period 2006–2014, which included the longest and quietest solar minimum of the past several decades, Venus Express (VEX) provided measurements of the photoelectron boundary (PEB) over the northern high-latitude region. Since the photoelectron boundary is closely related to the ionopause, we have an opportunity to analyze the EUV effect on the dayside ionopause by combining PVO and VEX observations. We have evaluated and then reduced the orbit bias effect in data from both PVO and VEX, and then used the results to derive a relationship between solar EUV level and the dayside ionopause altitude. We find that the dayside ionopause altitude increases as the solar EUV level increases, which is consistent with theoretical expectations.

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; We characterize the solar wind proton reflection (backscattering) from Phobos using a series of Mars Express operations. The plasma data obtained during the Phobos flyby of Mars Express in January 2016 showed a non-solar wind signal possibly reflected from the Phobos surface. Similar signatures were previously reported during an earlier Phobos flyby in 2008. On the other hand, although Mars Express has encountered Phobos (within 100 km) more than 10 times, it has thus far detected only two clear cases of reflected protons. The intermittency of the reflected proton detections could indicate that these protons are not from Phobos but are produced by the spacecraft body or solar arrays under a special attitude configuration during the flyby maneuver. To rule out these artifacts as the cause, we conducted three special operations; Mars Express was operated using the identical attitude and solar panel control sequence but without Phobos nearby. All the measured plasma data during the special operations exhibit no additional plasma signatures. These fake flyby experiments indicate that the measured non-solar wind protons during the real flyby are not from the spacecraft and that Phobos likely reflects solar wind into space. On the other hand, the intermittency of the reflected protons from Phobos remains unexplained. The reflected protons are vital additional plasma components because they inject enough energy to disturb the near-Phobos plasma environment. In addition, we can utilize these reflected particles to remotely measure the surface precipitation flux.

In Huybrighs et al., 2020 we investigated energetic proton depletions along Galileo's Europa flyby E26. Based on a particle tracing analysis we proposed that depletions are caused by perturbed electrogmagnetic fields combined with atmospheric charge exchange and possible plumes. One depletion feature identified as a plume signature was shown to be an artefact Jia et al., 2021. Despite that, here we emphasize that Huybrighs et al., 2020 demonstrates that plumes can cause proton depletions and that these features should be sought after. Furthermore, the conclusions on the importance of perturbed electromagnetic fields and atmospheric charge exchange on the depletions are unaffected. We suggest that the artefact's cause is a mistagging of protons as heavier ions by EPD. The artefact prevents us from confirming or excluding that there is a plume associated depletion. We also address comments on the MHD simulations and demonstrate that 540-1040 keV losses are not necessarily inconsistent with 115-244 keV losses by plume associated charge exchange., Comment: accepted to journal of geophysical research letters

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.

In order to determine the extent to which a global magnetic field is required for a planet to be habitable at its surface, expertise is required from diverse communities, some of which have diverged from each other over the past several decades. For example, modelers and observers of the terrestrial magnetosphere have limited overlap and interaction with modelers and observers of unmagnetized planets or the giant planets in our solar system. There is relatively limited interaction between any of the above communities and those who study exoplanets, though efforts are increasing to bridge the solar system and exoplanet communities. We describe a NASA Heliophysics DRIVE Science Center selected to answer the central question of this session: “Do Habitable Worlds Require Magnetic Fields”. This Center, named MACH (Magnetic Fields, Atmospheres, and the Connection to Habitability) includes scientists who study atmospheric escape from Earth, unmagnetized planets, and exoplanets. Over the next several years MACH will construct a framework that enables the evaluation of atmospheric loss from an arbitrary rocky planet, given information about the planet and its host star. The MACH Center hosted a community-wide workshop in June 2021 centered around this topic, and is seeking to grow their interactions with interested scientists from relevant disciplines.

IntroductionThe Venusian ionosphere interacts directly with the solar wind, and forms an induced magnetosphere. The interaction transfers energy from the solar wind to the ionospheric ions, and causes some ions to escape into the induced magnetotail (Futaana et al., 2017; Persson et al., 2020). In the magnetotail, the ions do not simply flow from Venus and outward to space. The ion flows have an additional component back towards Venus: return flows (Kollmann et al., 2016; Persson et al., 2018). These return flows was shown to decrease the total average escape rates from Venus for both H+ and O+ ions (Persson et al., 2018). In this study, we delve deeper into the structure of the ion flows in the magnetotail in order to provide further insight into these return flows. MethodTo analyse the ion flows we use the Ion Mass Analyser (IMA), a part of the ASPERA-4 instrument suite (Barabash et al., 2007b), on board Venus Express. IMA is a top-hat electrostatic analyser with an energy range of 0.01-36 keV, with ΔE/E=7%. The mass separating capabilities allows us to efficiently separate the lighter H+ from the heavier O+ ions. From the electrostatic deflector plates and the cylindrical symmetry the field-of-view has a resolution of 5.6x22.5˚ for each of the 16x16 pixels, which gives a total field-of-view of 90x360˚. We use the full dataset of IMA from 2006 to 2014 to calculate average ion velocity distributions. We combine the measurements by location in the magnetotail. As the induced magnetotail of Venus is structured by the direction of the upstream Interplanetary Magnetic Field (IMF) and the solar wind motional electric field (Jarvinen et al., 2013; McComas et al., 1986; Pérez‐de‐Tejada, 2001), we use the direction of the IMF to group the measurements together. The average ion distributions are then used to analyse the structure of flows in the magnetotail, in order to provide further insight in the return flow mechanisms. Results and discussionThe structure of the magnetotail with respect to the solar wind motional electric field implies a difference in the ion flows between the hemisphere where the electric field points away from Venus (+E) and the hemisphere where the electric field points towards Venus (-E). The magnetic field draping in the -E hemisphere provides a more narrow draping near the plasma sheet, which indicates a preference for magnetic reconnection (Zhang et al., 2010). If magnetic reconnection is the main mechanism that causes the return flows, we therefore expect a preference of return flows in the -E hemisphere. Preliminary results indicate that there is no clear dependence of the return flow with +E or -E hemisphere. In agreement with previous studies, our results show that the main anti-sunward acceleration in the magnetotail occurs in the +E hemisphere (Barabash et al., 2007a; Fedorov et al., 2011). However, the unclear relationship of the return flows with hemisphere warrants a further investigation. In this presentation, we present our results of an expanded study where we will have investigated the ion flows in the magnetotail in further detail to see if there is a preferred location or condition where the return flows are appearing. ReferencesBarabash, et al. (2007a). The loss of ions from Venus through the plasma wakes. Nature, 450(7170), 650–653. https://doi.org/10.1038/nature06434 Barabash, et al. (2007b). The Analyser of Space Plasmas and Energetic Atoms (ASPERA‐4) for the Venus Express mission. Planetary and Space Science, 55(12), 1772–1792. https://doi.org/10.1016/j. pss.2007.01.014 Fedorov, et al. (2011). Measurements of the ion escape rates from Venus for solar minimum. Journal of Geophysical Research, 116, A07220. https://doi.org/10.1029/2011JA016427 Futaana, et al. (2017). Solar wind interaction and impact on the Venus atmosphere. Space Science Reviews, 212(3‐4), 1453–1509. https://doi.org/10.1007/s11214‐017‐0362‐8 Jarvinen, et al. (2013). Hemispheric asymmetries of the Venus plasma environment. Journal of Geophysical Research: Space Physics, 118, 4551–4563. https://doi.org/10.1002/jgra.50387 Kollmann, et al. (2016). Properties of planetward ion flows in Venus' magnetotail. Icarus, 274, 73–82. https://doi.org/10.1016/j.icarus.2016.02.053 McComas, et al. (1986). The average magnetic field draping and consistent plasma prop- erties of the Venus magnetotail. Journal of Geophysical Research, 91(A7), 7939–7953. https://doi.org/10.1029/JA091iA07p07939 Pérez‐de‐Tejada, H. (2001). Solar wind erosion of the Venus polar ionosphere. Journal of Geophysical Research, 106(A1), 211–219. https:// doi.org/10.1029/1999JA000231 Persson, et al. (2018). H+/O+ escape rate ratio in the Venus magnetotail and its dependence on the solar cycle. Geophysical Research Letters, 124, 4597–4607. https://doi.org/10.1029/2018JA026271 Persson, et al. (2020). The Venusian atmospheric oxygen ion escape: Extrapolation to the Early Solar System. Journal of Geophysical Research: Planets, 125. https://doi. org/10.1029/2019JE006336 Zhang, et al. (2010). Hemispheric asymmetry of the magnetic field wrapping pattern in the Venusian magnetotail. Geophysical Research Letters, 37, L14202. https://doi.org/10.1029/2010GL044020

The JUpiter ICy moons Explorer (JUICE) of the European Space Agency will investigate Jupiter and its icy moons Europa, Ganymede, and Callisto, with the aim to better understand the origin and evolution of our Solar System and the emergence of habitable worlds around gas giants. The Particle Environment Package (PEP) on board JUICE is designed to measure neutrals, ions, electrons, and energetic particles over an energy range from eV to MeV. In the vicinity of Callisto, PEP will characterize the Jovian plasma environment and the outer parts of Callisto’s atmosphere and ionosphere. Roughly twenty Callisto flybys with closest approaches between 200 km and 5000 km altitude are planned over the course of the JUICE mission. This study aims at optimizing the scientific insight gained from the foreseen flybys by combining the input from the PEP science team and operation planning with recent model efforts for Callisto’s atmosphere, the plasma environment and the production of Energetic Neutral Atoms. The results of this study will inform both science operation planning of PEP and JUICE and they will guide future model development for Callisto’s atmosphere, ionosphere, and their interaction with the plasma environment.

International audience; We investigate the heavy ion density and velocity in the Venusian upper ionosphere near the North Pole, using the Ion Mass Analyzer, a part of the Analyzer of Space Plasmas and Energetic Atoms 4, together with the magnetic field instruments on Venus Express. The measurements were made during June-July 2014, covering the aerobraking campaign with lowered altitude measurements ( 130 km). The plasma scale heights are 15 km below 150-km altitude and 200 km at 150-400-km altitude. A clear trend of dusk-to-dawn heavy ion flow across the polar ionosphere was found, with speeds of 2-10 km/s. In addition, the flow has a significant downward radial velocity component. The flow pattern does not depend on the interplanetary magnetic field directions nor the ionospheric magnetization states. Instead, we suggest a thermal pressure gradient between the equatorial and polar terminator regions, induced by the decrease in density between the regions, as the dominant mechanism driving the ion flow.

We investigate dependences of O+ escape rates from Venus both on the solar wind and the solar extreme ultraviolet (EUV) flux by using the 8.5-year dataset (May 2006 to December 2014) of the Ion Mass Analyzer and the magnetometer aboard Venus Express. We examine the O+ escape rates for 8 different conditions depending on the solar wind's dynamic pressure, the magnitude of the motional electric field, and the solar F10.7 index which is a good indicator for the solar EUV flux. We find that the O+ escape rates are mainly controlled by the motional electric field and the solar EUV flux in the magnetosheath. We suggest that the ion pickup by the motional electric field is the main ion escape process in the magnetosheath. On the other hand, in the induced magnetosphere, the O+ escape rates are controlled by not only the solar wind and the solar EUV flux but also return flows. We find that the return flows become dominant in the magnetotail in the solar maximum period, which results in reducing the net escape rates in the induced magnetosphere. As a result, net escape rates tend to become larger in the solar minimum period than those in the solar maximum period. Further analysis of the magnetic field shows that the return flows are preferably observed when the magnetic field component along the Venus-Sun line reverses multiple times in the magnetotail. We suggest that ionospheric irregular structures or IMF sector boundary crossings form the fine scale anti-parallel draping pattern of the interplanetary magnetic field (IMF), and this causes ion acceleration towards Venus due to the magnetic tension force or magnetic reconnections. Another possibility is precipitations of O+ pickup ions on the nightside of Venus under the fine structure of IMF. Since the return flows significantly affect the O+ escape rates from Venus, it is important to study not only long-term transition of ion outflow from Venus but also return flows to estimate the net ion loss from Venus over the long history of the solar system.

Plasma channels have been suggested to account for the observation of ionospheric holes in the Venus nightside ionosphere. They are produced by the erosion of the solar wind on the magnetic polar regions of the Venus ionosphere, and are related to a sharp plasma transition that extends along the flanks of the wake and that is located downstream from the bow shock. The sharp plasma (intermediate) transition is a feature that has been detected with instruments onboard all the main spacecraft that have probed the Venus wake. From the early flyby transit of the Mariner 5 spacecraft to the later orbit crossings of the Venera 10, the Pioneer Venus and more recently the Venus Express there has been accumulated evidence of the presence of that transition by the flanks of the Venus wake. We report here measurements made with the ASPERA-4 instrument of the Venus Express that were conducted in orbit crossings by the midnight plane over a 4 year period (between 2006 and 2009), and that show different positions of the intermediate transition in the Venus wake at locations closer to the sun-Venus axis near solar minimum conditions by 2009. Measurements conducted in this latter time period also indicate that the intermediate transition by the midnight plane derives from the plasma channels and that is replaced by a broad velocity layer in orbits that probed farther away from that plane. It is argued that changes in the position of the intermediate transition with respect to the plasma channels are related to processes produced by the transport of solar wind momentum to the Venus polar ionosphere. The energy spectra of planetary ions measured in VEX orbits that probed by the midnight plane show momentum transport from the solar wind protons. This result is contrary to the conclusions reported by Collinson et al. (2014) in the sense that there is ¨no difference in the peak energy of the ionospheric outflow¨ when measured inside and outside an ionospheric hole.

Out of the two Venus flybys that BepiColombo uses as a gravity assist manoeuvre to finally arrive at Mercury, the first took place on 15 October 2020. After passing the bow shock, the spacecraft travelled along the induced magnetotail, crossing it mainly in the YVSO-direction. In this paper, the BepiColombo Mercury Planetary Orbiter Magnetometer (MPO-MAG) data are discussed, with support from three other plasma instruments: the Planetary Ion Camera (PICAM), the Mercury Electron Analyser (MEA) and the radiation monitor (BERM). Behind the bow shock crossing, the magnetic field showed a draping pattern consistent with field lines connected to the interplanetary magnetic field wrapping around the planet. This flyby showed a highly active magnetotail, with, e.g., strong flapping motions at a period of ~7 min. This activity was driven by solar wind conditions. Just before this flyby, Venus's induced magnetosphere was impacted by a stealth coronal mass ejection, of which the trailing side was still interacting with it during the flyby. This flyby is a unique opportunity to study the full length and structure of the induced magnetotail of Venus, indicating that the tail was most likely still present at about 48 Venus radii.