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The main goal of the radiation monitor RADEM flying onboard the ESA JUICE mission is to provide continuous information on particle fluxes and their energy spectra. The monitor measures electrons up to 40 MeV and protons up to 250 MeV. Such a range of energies detected by RADEM enables covering the most hazardous regimes in terms of radiation damage. Spectroscopic information on particle energies is provided using eight quasi-logarithmic energy bins. RADEM has also a dedicated heavy-ion detector designed to measure a variety of heavy ion species with their LET between 0.1 and 10 MeV/cm/mg-1. Moreover, the monitor contains an additional detector sensitive to the direction of incoming radiation. It expands the instrument's angular coverage up to 35% of the sky. Apart from its spectroscopic and angular distribution functions, RADEM will continuously provide values of the radiation dose deposited by each particle species. Its telemetry data will be stored in the data center for the JUICE mission operated by the European Space Astronomy Centre. After preprocessing the higher-level data will become available to the JUICE scientific team. RADEM will be switched on shortly after the JUICE launch planned for April 2023 and after a short commissioning phase will start its nominal operation. Apart from regular and short tuning and calibration periods, it will remain operating for the rest of the mission i.e. almost 10 years. While its primary purpose is to monitor the mission levels for safety concerns of the spacecraft and its scientific payload, its measurements open a unique opportunity for conducting real-time, continuous observations during its full cruise to Jupiter. RADEM will study all aspects of the radiation phenomena characteristic to the Earth and Solar System. Correlations with other instruments will allow for advanced observations of particle event propagation and a better understanding of processes related to the dynamics of particle environments including their links with solar activity and magnetic fields across the solar system. In particular, during its first two years of the cruise to Jupiter, RADEM will precisely map the radiation environment between Venus and Mars, providing uninterrupted time-resolved spectroscopy and dosimetry data from Solar Energetic Particles and Cosmic Rays.

With MaQuIs we propose a mission to investigate the gravitational field of Mars. Observing the gravitational field over time yields information about the planets tectonic lithoshphere, mass distribution, and composition. Consequently, this mission allows to study static and dynamic processes on and under the surface of Mars, including phenomena such as melting cycles and tectonic activity.MaQuIs will deploy quantum mechanical means to measure Mars gravitational field with the highest precision yet. In addition, the nature of the proposed instrumentation achieves high sensitivities without needing more complex satellite constellations. As such, MaQuIs follows successful missions for the Earth and Moon, extending the technology to Mars.In this presentation we will outline the expected scientific merit and explain the underlying technology and planned configuration of the mission.

Electron density structure and its temporal/spatial variations is one of the critical quantities in understanding an upper atmosphere. Mars has currently several orbiters studying its upper atmosphere and in particular electron density profiles. The Mars Express (MEX), in the orbit since 2003 has been measuring Mars upper atmosphere through remote measurements by the MARSIS (Sub-Surface Sounding Radar Altimeter) sounder and radio occultations by MaRS (Radio Science Experiment - sounding of the internal structure, atmosphere and environment). The Mars Atmosphere and Volatile EvolutioN, MAVEN mission whose science objectives include exploration of the interactions of the Sun and the solar wind with the Mars magnetosphere and upper atmosphere has complete plasma package. Maven has been performing in-situ composition measurements since November 2014, in particular, the Langmuir Probe and Waves (LPW) instrument onboard MAVEN provide electron density using current-voltage sweeps. Here we present the comparison of multi-instrument spacecraft measurements of Mars upper atmosphere for selected dates, using remote sensing (MEX) and in-situ measurements (MAVEN). The mutual observations are selected from publicly available data on ESA Planetary Science Archive as well as MAVEN Science Data Center. The L2 level Radio Occultation data are analyzed to obtain the Mars upper Atmosphere Electron density profiles. The MARSIS and LPW provide top side electron profiles whereas Radio occultations provide the full electron density profile. We focuse on the photochemical equilibrium region of the Martian ionosphere–thermosphere below 200 km. The analysis also includesz the Deep Dip campaigns of MAVEN making in-situ measurements of the region near the ionospheric peak. The comparison of independent measurements using different techniques will be presented and the differences and similarities between the observations will be discussed to help to validate our understanding of the physical and chemical processes occurring in the atmosphere. Figure 1: Comparison of MEX Radio Occultations (RO) with the MAVEN Langmuir Probe and Waves (LPW) for 3 selected mutual observation in March 2015

Radars in orbit around Mars such as MARSIS on Mars Express and SHARAD on Mars Reconnaissance Orbiter provide evidence for the nature of the surface and some sub-surface layers. We have now extended our earlier work, which has indicated solar energetic particles are responsible for the attenuation of the reflected MARSIS and SHARAD radar signals from the surface of Mars, often resulting in radar blackouts. The MARSIS instrument also operates in a topside sounding mode, the Advanced Ionospheric Sounder AIS mode), which also receives surface reflections and we now investigate the impact of the solar energetic particles on the surface reflection during ionospheric sounding observations made by MARSIS. We present observations during two intervals in December 2014 and in September 2017. MARSIS AIS was making observations on the nightside as Mars Express moved towards periapsis and then towards the dayside. The nightside AIS observations clearly demonstrate a similar loss of the surface signal to that seen in the MARSIS sub-surface mode. In addition there is evidence of a reflection from the enhanced layer created by the electrons which is responsible for the attenuation in the signal. The critical frequency is of order 1 MHz, which is equivalent to a peak electron density of order 1010 m-3, at an altitude of about 100 km. These characteristics are similar to our previous modelling work of the impact of the solar energetic electrons.

JUICE is ESA’s first large class mission to the outer Solar System. The main objectives of JUICE are to study Jupiter and its space environment with a special focus on Jupiter’s moons Europa, Ganymede, and Callisto, and their potential habitability. In order to fulfil these objectives, the JUICE measurements need to be accurately corrected for any possible perturbations. Here, we present Spacecraft Plasma Interaction Software (SPIS) simulations of the surface charging of JUICE in the solar wind. The results will be used to correct the future JUICE measurements for the impact of the charging. We have used a solar wind environment model (i.e. a description of the environment covering typical values for parameters such as electron and ion densities, temperatures, and velocities, magnetic field strengths, and EUV flux) for the location where JUICE will perform its first measurements, between 1500 and 3000 RE from Earth. The typical values for the solar wind parameters and the minimum and maximum values from the expected parameter ranges have been used to simulate the interaction in both average and “extreme” solar wind conditions. Here we present the main results from the SPIS simulations: the surface potential of the spacecraft; the potentials at the locations of the particle and field instrumentation such as the RPWI Langmuir probes and the PEP plasma analysers; the electron and ion density at the locations of the RPWI instruments and the PEP plasma analysers; the characteristics of perturbing particle populations such as photoelectron and secondary electron populations produced by the spacecraft itself; and the properties of the ion wake of the spacecraft. The detailed knowledge of the listed parameters will be used to provide accurate analyses of the first in-situ particle and field measurements performed by JUICE.

JUICE is the first large mission chosen in the framework of ESA’s Cosmic Vision 2015-2025 program. The focus of JUICE is to characterize the conditions that might have led to the emergence of habitable environments among the Jovian icy satellites, in particular Europa, Callisto and Ganymede. In addition, JUICE will also perform a multidisciplinary investigation of the Jupiter system as an archetype for gas giants. To address those key science objectives, the spacecraft payload consists of 10 state-of-the-art instruments (and one experiment that use the spacecraft telecommunication system with ground-based instruments) that will perform remote and in-situ measurements of Jupiter, its moon and their environment. From a trajectory’s point of view, the mission calls for a three-year orbital survey of the Jupiter System designed as a sequence of 67 orbits around the planet of different periods and inclinations, and includes 35 flybys of Europa (2), Ganymede (12) and Callisto (21). The second part of the mission will devote an additional 9 months in orbit around Ganymede for an in-depth characterization of Ganymede as a planetary object and possible habitat. By its touring nature and due to the diversity of science targets and different disciplines involved in the mission, the development of an observation plan will often face conflicting observations opportunities, also limited in resources as a consequence of the large helio- and geo-centric distances at play. The Science Operations Center, together with the Project Scientist and the Science Working Team, are in charge of setting up and developing a science planning strategy for the mission to ensure that the prime science objectives of the mission are addressed while remaining compatible with the mission constraints. The JUICE Science Planning Process for the Jupiter tour consists of two main pillars: Segmentation of the trajectory. Based on the Cassini heritage, this activity relies on the analysis of all science opportunities along the tour to subsequently support the decision on selecting a prime scientific objective that will get priority in terms of resources (data volume, power and pointing) for a specific time window (a.k.a segment). Taking into account known operational activities’ constraints (navigation, wheel off-loading etc) and high-level resources’ estimate, an analysis of the expected scientific coverage and resource status along the tour is performed, and several iterations between the different disciplines experts (through the science working groups) take place to converge towards a plan that should ensure that prime science objectives of the mission are fulfilled within the operational constraints of the mission. Detailed sizing case analysis for science operations: For specific operationally of scientifically challenging sections of the segmentation, in-depth analysis is needed in order to refine resources assumptions (attitude, power and data volume) made at segmentation level. Those detailed analysis, performed down to observation level, is done in collaboration with the instrument teams. The present work will describe the different steps and groups involved in the science planning, the current status of the segmentation, and the detailed analysis of the first JUICE Europa flybys will be presented.

BepiColombo is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) to the planet Mercury. It was launched in October 2018 and it is due to arrive at Mercury in late 2025. It consists of two spacecraft, the Mercury Planetary Orbiter (MPO) built by ESA, and the Mercury Magnetospheric Orbiter (MMO) built by JAXA, as well as a Mercury Transfer Module (MTM) for propulsion built by ESA. The cruise phase to Mercury will last ~7 years and constitutes an exceptional opportunity for studying the evolution of the solar wind, solar transients, as well as for planetary science and planetary space weather. On this last topic, BepiColombo is proving to be an important upstream solar wind monitor for the terrestrial planets. This is especially important for case of Mars where we currently do not have many observations of the upstream interplanetary magnetic field or solar wind. As consequence, the analysis and interpretation of ionospheric observations is challenging, especially when coronal mass ejections and solar energetic particles hit Mars and we do not have Earth plasma observatories in good alignment with Mars to provide the space weather context. While Mars missions such as Mars Express or MAVEN are able to investigate the impact of the solar wind on the ionosphere, BepiColombo can be the solar wind sentinel for Mars, so we can see the cause and effect. Therefore, this work focuses on the response of the Martian ionosphere to solar transient events which have been previously detected by BepiColombo, and for which we can provide the right upstream solar wind context, such as during the last months of 2021. The objective is to evaluate the response of the Martian ionosphere and its dynamics with more accuracy knowing the exact energy inputs from the solar wind as detected in-situ in the solar wind by BepiColombo.

Space weather events are one of the many major factors affecting the escape and evolution of Martian atmosphere. The Sun-planet interaction is affected by several factors such as the heliocentric distance, chemical composition of the atmosphere, solar illumination and its intrinsic magnetic field. Mars has a varied environment of magnetic field. It has little or no intrinsic magnetic field, but there exist some strong, crustal magnetic field patches. Thus, it becomes one of the solar system's best models for understanding the interaction of weakly ionized plasma with a highly irregular magnetic field. Martian ionosphere owes its existence to the photoionization of neutral species by solar extreme ultraviolet (EUV) and X-ray photons. Martian ionosphere has a stratified structure with two main layers in its electron density profile (Ne). The primary layer (M2 layer) is formed by solar EUV radiation (~20-90 nm) and has a peak electron density at around 120-140 km altitude with a peak density of ~1011 m-3. The second layer (M1 layer) occurs at lower altitude with a peak electron density of ~109 m-3 and is formed by solar soft X-ray and electron impact ionization. The electron densities and the altitudes at which these peaks are very variable. Radio Occultation (RO) experiments are the first and major explorer of the Martian ionosphere and electron density profiles. RO experiments precisely measure the Doppler shift observed on the link between a planetary spacecraft and Earth, as the spacecraft passes into occultation behind the planet. The RO data can be processed to extract the vertical electron density profiles of the ionosphere. Apart from vertical electron density profiles, RO can also provide density, temperature and pressure profiles of the neutral atmosphere. Thus, it is also a powerful tool to understand the both the neutral atmosphere and ionosphere. Here we study the effect of solar flares and coronal mass ejections on the whole Martian atmosphere using the publicly available Mars Express radio occultation data from ESA Planetary Science Archive (PSA). For this, we selected two major solar disturbed periods occurred during 6th to 13th of June 2011 and 16th February to 31st March 2015. Using the Level 2 data we calculated the Ne profiles in the ionosphere as well as the temperature profiles of lower atmosphere. We also compare our results with numerical models and available measurements like MARSIS and Langmuir probe on NASA's MAVEN in the selected period. Figure 1: a. Electron density profiles observed by MEX on 2011 following a solar event on the 8th of June 2011.

Some of the atmospheric processes occurring in the Ice Giant planets Uranus and Neptune critically depend on the electrical properties of their respective atmospheres. Therefore, the modelling of the electromagnetic properties of the atmosphere provides valuable information to characterize several aspects of the atmosphere. For example, lightning phenomena is an indicator of strong convective movements, and the number densities of electrons and ions affect the growth of aerosols and cloud formation. In the pressure range where such process take place the solar radiation has been mainly absorbed and the main ionization source is galactic cosmic rays. Furthermore, the long distance to the Sun decreases the role of solar radiation on the atmospheric electrical properties, while the cosmic ray flux is similar or even larger compared to that at the inner solar system. This implies a proportionally greater role of the galactic cosmic rays induced ionosphere for the ice giant planets than for the rest of solar system planets. Protons and alpha particles, which mainly compound the cosmic rays, can reach the Uranus and Neptune lower stratosphere to ionize the atmospheric constituents and thus produce a low altitude ionospheric layer. The flux and composition of cosmic ray incident on a planetary atmosphere depend on the distance to the Sun and varies over the 11-year solar activity cycle. Furthermore, the planetary magnetic field deflects the incoming cosmic rays depending on their rigidity and angle of incidence. Therefore, both factors solar cycle and magnetic latitude must be considered to calculate the ionization rate by cosmic rays. The presence of aerosols also affects the ion-neutral chemistry by capturing electrons and positive ions depending on the aerosol size and concentration. Here we present the first results obtained with a numerical model, which is based on previous studies for Mars and Titan [1-2], capable to calculate the number density of electrons and positive ions, as well the aerosol charging between 0.1 and 15 bars in the atmosphere of Neptune and Uranus. We have found that, for the particle density and size vertical profiles obtained in previous works [3-4], aerosols are negatively charged, and the number density of electrons is lower than that of positive ions for pressures lower than around 1 bar. References [1] Cardnell, S., et al. (2016), A photochemical model of the dust-loaded ionosphere of Mars, J. Geophys. Res. Planets, 121, doi:10.1002/2016JE005077. [2] Molina-Cuberos, G.J., et al. (2018) Aerosols: The key to understanding Titan's lower ionosphere, Planet. Space Sci, 153, 157 – 162, doi: 10.1016/j.pss.2018.02.007. [3] Toledo et al. (2019), Constraints on Uranus's haze structure, formation and transport, Icarus 0019-1035, doi: 10.1016/j.icarus.2019.05.018 [4] Toledo et al. (2020) Constraints on Neptune’s haze structure and formation from VLT observations in the H-band, Icarus, doi: 10.1016/j.icarus.2020.113808

Icy moons of Jupiter and Saturn are privileged targets in currently developed space missions by several space agencies and in particular ESA, NASA and their partners. One of these missions is ESA’s first large mission in the Cosmic Vision Programme, JUICE [1], which is being developed to address questions regarding the Jupiter system and its satellites, with a focus on the largest moon, Ganymede. The overarching theme for JUICE is the emergence of habitable worlds around gas giants taking into account the requirements involving the presence of organic compounds, trace elements, water, energy sources and a relative stability of the environment over time.Among other, JUICE will determine the characteristics (composition and dynamics) of the exospheres of the icy moons [2], in particular Ganymede and Europa, with for instance coordinated observations among sets of instruments like UVS, PEP, RPWI, MAJIS, 3GM, J-MAG, JANUS and SWI. The JUICE mission is scheduled to be launched in spring 2023 and arrive at Jupiter in mid-2031 and is foreseen to last nominally for 3 and a half years. JUICE investigations will benefit from current observations by JUNO and will be synergistic to NASA’s Europa Clipper mission. I will describe the foreseen investigations of the tenuous atmospheres of the icy moons around Jupiter.Cassini explored the dense and organic-laden atmosphere of Titan during several flybys over 13 years [2,3] and also determined the characteristics of the Enceladus plumes. However, new questions have risen and several cold cases [4] remain that will constitute major science objectives for future space missions to the satellites around Saturn, like Dragonfly [5] or an orbiter in the Saturn system or a dedicated Enceladus mission…In particular, Titan’s atmosphere has not yet revealed all its secrets, in particular for the chemical composition, which should be much more complex than what was detected by Cassini-Huygens. Future in situ measurements will be extremely useful in unveiling this unique complex world. In the meantime, ground-based observations with large telescopes like ALMA, elsewhere in Chile or the ones in Hawaii can help complement the past discoveries.References:[1] Coustenis, A., Witasse, O., Erd, C., 2021. The JUICE mission: expectations and challenges. Fall issue of The Bridge on space exploration, Sept. 2021, Vol. 51, issue #3, pp. 41-50.[2] Coustenis, A., Tokano, T., Burger, M. H., Cassidy, T. A., Lopes, R. M., Lorenz, R. D., Retherford, K. D., Schubert G., 2010. Atmospheres/exospheres characteristics of icy satellites. Space Sci. Rev., 153, 155-184. https://www.nae.edu/260902/The-JUICE-Mission-Challenges-and-Expectations[3] Coustenis, A., 2021. “The Atmosphere of Titan”. In Read, P. (Ed.), Oxford Research Encyclopedia of Planetary Science. Oxford University Press (August 31). doi: https://doi.org/10.1093/acrefore/9780190647926.013.120[4] Nixon, C. A., Lorenz, R. D., Achterberg, R. K., et al. (2018). Titan's cold case files - Outstanding questions after Cassini-Huygens. Planetary and Space Science, 155, 50-72.[5] Barnes, J. et al. (2021). Science Goals and Objectives for the Dragonfly Titan Rotorcraft Relocatable Lander. The Plan. Sci. J., VoL. 2, Issue 4, id.130, 18 pp.

International audience; We present the first long-term characterization of ionization layers in the lower ionosphere of Mars (below ∼90 km), a region inaccessible to orbital in-situ observations, based on an analysis of radar echo blackouts observed on Mars Express and the Mars Reconnaissance Orbiter from 2006 to 2017. A blackout occurs when the expected surface reflection is partly or totally attenuated for portions of an observation. Enhanced ionization at altitudes of 60-90 km, below the main ionospheric electron density peak, leads to increased absorption of the radar signal, resulting in the blackouts. We find that (a) MARSIS, operating at frequencies between 1.8 and 5 MHz, suffered more blackouts than SHARAD, which has a higher carrier frequency (20 MHz), (b) there is a clear correlation of blackout occurrence with solar cycle, (c) there is no apparent relationship between blackout occurrence and crustal magnetic fields, and (d) blackouts occur during both nightside and dayside observations, although the peak occurrence is deep on the nightside. Analysis of Mars Atmosphere and Volatile EvolutioN Solar Energetic Particle electron counts between 20 and 200 keV demonstrates that these electrons are likely responsible for attenuating the radar signals. We investigate the minimum SEP electron fluxes required to ionize the lower atmosphere and produce measurable attenuation. When both radars experience a blackout, the SEP electron fluxes are at their highest. Based on several case studies, we find that the average SEP spectrum responsible for a blackout is particularly enhanced at its higher energy end, that is, above 70 keV.

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; We study the influence of the solar extreme ultraviolet (EUV) flux intensity on the precipitating ion fluxes as seen by the Solar Wind Ion Analyzer, an energy and angular ion spectrometer aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We defined three periods with significantly different EUV flux intensity (1.6 and 3.2 times the lowest EUV intensity) and compare the precipitating ion flux measured by MAVEN/Solar Wind Ion Analyzer during each period. At low energy [30–650] eV, we find that the median (average) precipitating ion flux during the medium and low EUV periods are, respectively, 1.7 (2.1) and 3 (3.5) times more intense than the flux during the high EUV period. At high energy [650–25,000] eV, a similar trend in the intensity of the precipitating ion flux is observed but with an increase by 50% (46%) and 70% (79%), respectively. A larger EUV flux does therefore not seem to favor heavy ion precipitation into Mars's atmosphere, contrary to modeling prediction and overall expectations.

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) onboard Mars Express, which operates between 0.1 and 5.5 MHz, suffered from a complete blackout for 10 days in September 2017 when observing on the nightside (a rare occurrence). Moreover, the Shallow Radar (SHARAD) onboard the Mars Reconnaissance Orbiter, which operates at 20 MHz, also suffered a blackout for three days when operating on both dayside and nightside. We propose that these blackouts are caused by solar energetic particles of few tens of keV and above associated with an extreme space weather event between 10 and 22 September 2017, as recorded by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Numerical simulations of energetic electron precipitation predict that a lower O-2(+) nighttime ionospheric layer of magnitude similar to 10(10) m(-3) peaking at similar to 90-km altitude is produced. Consequently, such a layer would absorb radar signals at high frequencies and explain the blackouts. The peak absorption level is found to be at 70-km altitude. Plain Language Summary Several instrument operations, as well as communication systems with rovers at the surface, depend on radio signals that propagate throughout the atmosphere of Mars. This is the case also for two radars that are currently working in Mars' orbit, sounding the ionosphere, surface, and subsurface of the planet. In mid-September 2017, a powerful solar storm hit Mars, producing a large amount of energetic particle precipitation over a 10-day period. We have found that high-energy electrons ionized the atmosphere of Mars, creating a dense layer of ions and electrons at similar to 90 km on the Martian nightside. This layer attenuated radar signals continuously for 10 days, stopping the radars to receive any signal from the planetary surface. In this work, we assess the properties of this layer in order to understand the implications of this kind of phenomenon for radar performance and communications.

The upcoming JUpiter ICy moons Explorer (JUICE) (ESA) and Europa Clipper (NASA) missions will perform detailed observations of the giant gaseous planet Jupiter and three of its largest moons (Ganymede, Callisto, and Europa). A series of experiments was performed to measure the thermal conductivity and calorimetry of macroscopic frozen salt solutions of particular interest in Jovian icy moons. The following salts were investigated: Na-chloride (NaCl), Mg-sulphate (MgSO4), sodium sulphate (Na2SO4), and Magnesium chloride (MgCl2). Measurements were performed at atmospheric pressure and temperatures from 0 to -70ºC in a climatic chamber. Temperature and thermal conductivity were measured during the course of the experiments. A small sample of the liquid salt-water solution was set aside for the calorimetry measurements. A side effect of the measurements is that they served to spot phase changes in the ice mixtures with high sensitivity. An important result is that, the phase changes observed in the standard calorimetric tests, could be monitored in situ with high sensitivity in the thermal conductivity measurements. Indeed, when a phase change occurs, a large peak appeared in the thermal conductivity values as the result of the natural heat release that accompanied the phase change.

Radio Occultation (RO) is a very powerful technique to probe a planetary atmosphere, in providing vertical density profiles of the neutral atmosphere and ionosphere. The standard method uses a radio link between a spacecraft and an Earth ground station. Nevertheless, the possibility to obtain information about the Martian atmosphere with mutual RO events, using data from NASA Mars Odyssey and Mars Reconnaissance Orbiters (MRO), has been demonstrated by Ao et al. (2015).Taking advantage of two European spacecraft in orbit around Mars, the European Space Agency is currently preparing experiments of mutual RO between Mars Express (MEX) and the ExoMars Trace Gas Orbiter (TGO). In preparation of MEX and TGO data inversion and analysis, a simulation-based strategy has been adopted and an algorithm able to retrieve vertical electron density profiles from Doppler shift measurements has been implemented and validated. Subsequently, in order to test the mentioned algorithm with experimental data, the same three RO events considered in the paper by Ao et al. (2015) have been processed. In particular, for each RO event, having the information about the satellites’ orbit, the (excess) Doppler shift values corresponding to the Mars Odyssey-MRO ray-paths have been converted to bending angles as a function of impact parameter. Then, assuming a spherical symmetry (Fjeldbo et al., 1971) for the ionosphere electron density, the bending angles have been transformed (through Abel integral) to a vertical refractivity profile, which, in turn, has been converted to an ionospheric electron density profile.In this work, the results obtained by the application of the mentioned inversion algorithm to experimental data will be presented, with particular focus on the retrieval of the ionospheric electron density profiles. References Ao, C. O., C. D. Edwards Jr., D. S. Kahan, X. Pi, S. W. Asmar, and A. J. Mannucci (2015), A first demonstration of Mars crosslink occultation measurements, Radio Sci., 50, 997–1007, doi:10.1002/2015RS005750. Fjeldbo, G., A. J. Kliore, and V. R. Eshleman (1971), The neutral atmosphere of Venus as studied with the Mariner V radio occultationexperiments, Astron. J., 76, 123–140.

Ganymede is the only moon in our Solar System known to have its own global magnetic field, which generates a miniature moon magnetosphere inside the Jovian magnetosphere. Due to this unique characteristic of Ganymede, its auroral zone is also of particular scientific interest, as it is the only known example of this specific kind of interaction. The JUICE spacecraft will orbit Ganymede for almost a year, with a high inclination orbit with multiple auroral zone crossings. JUICE will study the auroral zone of Ganymede in more detail than ever before, providing both in-situ and remote sensing observations. In this work, we use Spacecraft Plasma Interaction Software (SPIS) simulations to study the spacecraft charging of JUICE in the auroral zone. Hubble Space Telescope observations of the aurora of Ganymede show localized regions of bright spots superimposed on a continuous background emission (e.g. Feldman et al. 2000, Eviatar et al. 2001). In order to produce bright auroras, the electron population needs to be accelerated up to hundreds of eV (Eviatar et al. 2001). Preliminary simulation results, using an auroral electron population with temperature Te = 200 eV and density ne = 300 cm-3, shows frame charging (i.e. spacecraft ground) of around 10 V and differential charging of around 30 V. High frame and differential potentials can cause disturbances in both particle and electric field measurements and prevent accurate characterization of the environment. Since the auroral zone of Ganymede is of particular scientific interest, it is important to study and prepare for this kind of disturbances. References D. Feldman et al., HST/STIS ultraviolet imaging of polar aurora on Ganymede, The Astrophysical Journal, 535(2), 2000 A. Eviatar et al., Excitation of the Ganymede ultraviolet aurora, The Astrophysical Journal, 555(2), 2001

Conventional Radio Occultation measurements take place between a spacecraft in orbit around a planet (or during an occasional fly-by), and a receiving ground station on the Earth. When the straight line between the sender and receiver crosses the ionosphere and the atmosphere of the planet the signal is affected by the electrons in the ionosphere and the molecules in the neutral atmosphere. This signal change is observed as a slight frequency shift in the received radio signal with respect to the transmitted signal. The shift is very small compared to the Doppler shift in the frequency due to the differential relative velocity of the spacecraft and the Earth, but can for a stable system be isolated, and profiles of electron density in the ionosphere and profiles of atmospheric density in the neutral atmosphere can be derived. Here we are attempting to do occultation measurements between two spacecraft at Mars, Mars Express and ExoMars Trace Gas Orbiter, using the UHF link normally used for communicating between the orbiters and the landers on the surface of Mars, rather than using the X- or S-band transmitter used for the communication between a spacecraft and the Earth. This was first exercised between NASA’s Odyssey and MRO at three occasions in 2007 (Ao, et al., Radio Sci., 2015), but has not been repeated since then. Such a Mutual Occultation technique has several significant advantages over the traditional spacecraft to Earth occultation measurements. In particular, it allows a much more even distribution of the samples over the surface of the planet and in time, and the observations are independent of Earth occultation seasons. Due to the short period of the orbit of TGO many occultations take place every day. The distance between the two spacecraft is much smaller than the distance to the Earth and therefore a much higher signal to noise ratio can be achieved, resulting in very low statistical errors. The Mutual Occultation s/c to s/c link also avoids that the signal passes through the Earth’s ionosphere and atmosphere. The compensation for the Earth atmosphere and ionosphere is far from perfect and results in major contributions to the systematic errors. An additional positive effect is that the interplanetary plasma disturbance to the signal is a minimum due to the short distance between the two s/c and the large distance from the Sun. The first experiment was carried out on the 2nd of November 2020 and demonstrated the feasibility of the technique. Several more experiments took place during November-December. These initial test used a lander (Beagle2) hail signal from Mars Express/Melacom, consisting of a series of 20 seconds of modulated and unmodulated transmissions interspersed with 2 seconds without transmission. In March 2021 a software update was applied to Melacom, which allowed it to generate an uninterrupted, unmodulated carrier-only signal, since. This has improved the performance and the quality of the measurements significantly. To date four passes with this improved performance have been executed. These data are presently being analysed. This presentation will summarise recent simulations and show the latest results from these new experimental measurements. Example of Occultation Geometry: The orbits of TGO and MEX are indicated by tan respective red lines and the direct path of the radio signal is indicated by a white line. The part of the propagation through the atmosphere is indicated by a yellow box.

Studying the presence of water and characterizing the tectonic structure in the firsts tens of kilometers of the crust of the Galilean icy moons are crucial to understand the formation and evolution of these bodies and could provide an insight into the setting for extra-terrestrial life within our solar system (Nimmo and Pappalardo, 2016). The most promising technique for directly detecting subsurface oceans is a penetrating radar and the use of low frequencies (< 30 MHz) is preferred to probe the moons' subsurfaces since the losses due to the surface roughness and absorption of the ice are reduced (Bruzzone et al., 2011). However, Jupiter has a loud radio environment for frequencies < 40 MHz (Cecconi et al., 2012), and the use of a passive mode, which would exploit Jupiter’s decametric radio emissions, is considered to operate the radar with low frequencies in the sub-Jovian hemispheres. However, the passive radar operates in a complex bistatic 3D geometry where Doppler and delay information are not separable. This justifies the use of simulations with realistic orbitographies to identify which configurations will lead to the best and worst performances, which is necessary to establish the scenarios of observation of the radar. In this paper, we compute the impact of the geometry on the final bistatic performances, using planned Juice orbits. In order to study the influence of the geometry only, we do not take into consideration the stochastic character of Jupiter’s noise. The emission is then a simple impulsion located in the Jupiter auroral coronas: we regard four sources, at the Eastern and Western borders of Jupiter’s North and South auroral coronas, as presented in Figure 1. In this geometry, the passive radar is orbiting around Ganymede and studies the reflection of the Jovian signal by a point target at the nadir in a monostatic geometry, or a point making a specular reflection in the bistatic case. To recognize weak, delayed, and Doppler-shifted contributions of the Jovian signal (also called reference signal), cross-correlation is carried out between the registered Jovian signal and the measured reflection. The next signal processing is the computation of the SAR synthesis to retrieve a Range-Doppler map of the surface probed. Figure 1. Considered location for the four sources of emission of Jupiter’s radio emissions, and Jupiter. The sources will then be referred to as red source, blue source, yellow source, and green source. To compute the performances of the radar, we simulate the signal scattered in monostatic and bistatic cases, for three different scenarios (figure 2, table 1) using different integration times, perform SAR synthesis and compute on the images the size of the resolution cell. We depict in table 2 the area of the resolution cell for each scenario, as well as the size of the Fresnel zone. The area of the resolution cell is always better than the size of the Fresnel zone, but table 2 depicts that with an integration time of one minute, probing close to the center of the sub-Jovian hemisphere provides the best resolution (1.33 km²). However, this conclusion changes when the integration times are increased to two minutes, and probing with an incidence angle of 38° becomes more favorable than along the nadir (0.28 km²). Indeed, in this geometry, the Range and Doppler sidelobes are not separated, and this non-separability increases with the integration. Thus, while the along-track resolution is predictably worsened in the bistatic case compared to the monostatic scenario and improves with increasing integration time, the resolution in across-track varies as well with the integration time. For orbit 2, it improves with an increasing integration time, while, for orbit 1 and 3, which are aligned with nadir, the integration time does not seem to largely impact it. This means that, while probing along the center of the sub-Jovian hemisphere seems more efficient with small integration times, probing different parts of the sub-Jovian hemisphere might become of interest if increasing the integration time is possible. This study showed that, as expected, the resolutions obtained are largely dependent on the geometry, but as well on the integration time. These conclusions will have to be kept in mind will preparing the probing strategy of Jupiter’s moons. Figure 2.Left: JUICE orbits as visualized on Cosmographia (https://www.cosmos.esa.int/web/spice/cosmographia)Right: Position of the three considered orbits ( orbit n°1 in red, orbit n°2 in green, and orbit n°3 in cyan), with the bistatic specular point in bright color, and the nadir point with an opacity. Table 1 Description of each scenario. Orbit Associated color Date Center Time Incidence Orbit n°1 Red 18/03/2033 15:41 2 Orbit n°2 Green 21/03/2033 09:46 38 Orbit n°3 Cyan 27/04/2033 08:02 27 Table 2 Performances resulting from each orbit. ρ2 is the area of the resolution cell while Fresnel depicts the area of the Fresnel zone. ρ2 (km2) Fresnel (km2) Orbit n°1 1 mn Monostatic 0.503 22 Bistatic 1.33 38 2 mn Monostatic 0.25 22 Bistatic 0.655 38 Orbit n°2 1 mn Monostatic 0.518 22 Bistatic 1.78 55 2 mn Monostatic 0.25 22 Bistatic 0.28 55 Orbit n°3 1 mn Monostatic 0.518 22 Bistatic 1.92 46 2 mn Monostatic 0.28 22 Bistatic 0.953 46

Mars Express has been exploring Mars since late 2003 giving us fascinating views of the red planet as well as unique science insights. The long-life of Mars Express is an asset in order to understand the long-term evolution of the atmosphere of Mars, and in particular, of the ionosphere and upper atmosphere. Currently, we have about 16 years of ionospheric observations at Mars, which cover near two cycles of solar activity. This is the first time that such a long time series observations can be investigated in other planet rather than Earth. In particular, this work focuses on Mars’ ionospheric behaviour during two consecutive solar minima (23/24 and 24/25) using the same dataset. We use the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board Mars Express to investigate the total electron content behaviour of the whole atmosphere in relation to key parameters, such as the solar flux, solar illumination, dust storms and Sun-Mars distance. The topside variability of the ionosphere is also investigated through variations in the neutral scale height, and results are supported by ionospheric modelling. The main goal of this study is to investigate whether the ionosphere during the recent solar minimum 24/25 was similar (and to which degree) to the ionosphere at solar minimum 23/24, which was characterised by a pronounced reduction of both the topside and bottomside regions.

ESA and NASA will launch two missions to explore the main Galilean moons of Jupiter in the coming years, JUpiter ICy moons Explorer-JUICE and Europa Clipper, respectively. Both missions will be able to determine the distribution of the potential habitable zone in the upper dozens of kilometers of the ice bodies by using onboard radar instruments [Bruzzone et al. 2013, Grasset et al., 2013, Phillips and Pappalardo 2014, Aglyamov et al. 2017]. Considering the possible presence of mixtures of water with salts, volatiles, and clays in the ice and liquid layers, we performed laboratory experiments to obtain the electrical properties of these chemical systems at solid and liquid state, and at different pressure conditions (Table 1). The results that we present at the conference will facilitate the interpretation of the future data received from the radar sensors. We measured the dielectric properties of these samples with a BDS80 Broadband Dielectric Spectroscopy system (Novocontrol), which allows working in a frequency range from 1 Hz to 10 MHz and temperatures from 143 to 323 K. Both, real permittivity (ε´) and electric conductivity (σ) were measured at 0.1 MPa while cooling the samples in temperature steps of 10 K. From these data, we calculated the activation energy and the attenuation of the radar wave depending on the chemical composition, the temperature of the sample, and the frequency of the applied electric field [Petrenko and Whitworth 1999, Pettinelli et al. 2015]. Conductivity measurements at high pressure were carried out using a modification of a chamber used previously for planetary simulation experiments (Muñoz-Iglesias et al. 2019). It is based on a stainless steel cylinder, which has different access on the bases and along the main body. Pressurization of the sample is carried out by water or gas from one access at the chamber base, while a sapphire window is at the opposite side for visual control and spectral analysis. Connections throughout the body of the cylinder are for the thermocouple, the pressure gauge and a special one to plug in the electrical sensor. The key feature is the plug for in-situ conductivity measurements with feed through wires connected to the probe, made of two Pt electrodes placed in a PTFE structure in order to maintain the configuration and to ensure the distance between electrodes (around 500 micrometers). Both electrodes have connections to isolated copper wires, which pass through the cell body to be connected to the signal transducer and the computer to record the data. Acknowledgements This work was supported by the ESA contract number 4000126441/19/ES/CM. We thank Anezina Solomonidou for assistance in the project proposal. References Aglyamov et al. (2017) Bright prospects for radar detection of Europa’s ocean, Icarus, 281, 334-337. Bruzzone et al. (2013) RIME: Radar for Icy moon Exploration, IEEE International Geoscience and Remote Sensing Symposium - IGARSS, Melbourne, 3907-3910. Grasset et al. (2013). Jupiter Icy moons explorer (JUICE): an ESA mission to orbit Ganymede and to characterise the Jupiter system. Planet. Space Sci. 78, 1-21 Muñoz-Iglesias et al. (2019). Experimental Petrology to Understand Europa's Crust. JGR-Planets 124, 2660-2678 Phillips and Pappalardo (2014). Europa Clipper mission concept: exploring Jupiter’s ocean moon. Eos Trans. AGU 95, 165-167. Pettinelli et al. (2015) Dielectric properties of Jovian satellite ice analogs for subsurface radar exploration: A review. Reviews of Geophysics, 53, 593-641.

ESA’s Mars Express spacecraft has been exploring the red planet since January 2004. The spacecraft is able to receive and transmit signals at both S-band and X-band. Changes in the radio signals properties while propagating through the atmosphere yield information on the electron density profile. The Mars’ ionosphere is very variable in time. One source of its variability is the solar activity. Here we study the effect of solar flares and coronal mass ejections on the Mars’ ionosphere using the publicly available Mars Express radio occultation data. A new software in python was developed to process the residual frequencies data sets, and was validated using higher-level archival data. We calculate the electron density profiles before, during, and after such solar events. The variations in ionospheric parameters (total electron content, peak density and altitude) are quantified in order to understand the ionospheric changes due to solar activity. As expected, significant variations in these parameters have been identified. The results are compared with additional measurements and models. Figure 1: Electron density profiles observed by MEX on 2011 during 2 days following a solar event.

JUICE - JUpiter ICy moons Explorer - is the first large mission in the ESA Cosmic Vision 2015-2025 programme. The mission was selected in May 2012, and is now (May 2021) in the final stages of its integration and testing campaigns. Following its arrival at Jupiter in July 2031, JUICE will spend 4.2 years making detailed observations of Jupiter and three of the Galilean moons, Ganymede, Callisto and Europa. We present here the plan of activities to be carried out during the interplanetary cruise phase. 1. Trajectory during the cruise phase The mission will be launched from Kourou with an Ariane 5. The baseline launch window is between 26 August – 15 September 2022, with a backup launch slot in August 2023. The interplanetary transfer sequence relies on gravity assist manoeuvres with Venus, Earth and the Moon. The Jupiter orbit insertion will be performed in July 2031. The cruise phase officially starts after the end of the near-Earth commissioning (launch + 3 months) and ends six months before the Jupiter orbit insertion, when the nominal science mission begins. The list of planetary gravity assists is given in Table 1: Date Planet Pericenter altitude [km] 01/09/2023 02/09/2023 Moon Earth 300 180,000 23/08/2024 Earth 13,400 31/08/2025 Venus 5,100 29/09/2026 Earth 8,600 18/01/2029 Earth 4,600 2. Spacecraft and mission constraints during the cruise phase The main limitations during the cruise phase are: Priority of operations in support of navigation and spacecraft safety, especially in the preparation of gravity assist manoeuvres, in particular the world premiere of Lunar-Earth gravity assist The thermal design of the spacecraft which imposes, for heliocentric distances lower than 1.34 AU, restricted pointing capabilities and limitations in the number of instruments that can operate simultaneously. Quiet Cruise baseline: Reduced number of ground contacts (one ground station pass per week except for planetary flybys). Operational constraint to minimize the use of the mass memory during Cruise to preserve unit lifetime, limiting the possibility to operate the instruments and store their data. Budgetary restrictions that result in small operation teams during this phase. The baseline operations of the instruments are two one-week checkouts per year. It is expected that at least some of the observations will take place during the planetary flybys, with different possibilities still under study. The requests for operating the payload beyond this baseline will be carefully analyzed and agreed on a best-effort basis. The next section gives example of possible observations. 3. Potential scientific investigations to be performed during the cruise phase Instrument operations during the cruise phase are always useful: they allow calibrating instruments in known environments (e.g. solar wind, Earth’s magnetosphere), checking possible interferences between instruments, they provide scientific results (sometimes not expected and outstanding, resulting in high standard publications) and attract public attention. During the long cruise phase of the JUICE mission, a number of scientific opportunities have been identified, beyond the obvious case of the planetary flybys. They include: solar wind campaigns, neutral atoms imaging in the heliosphere, measurement of Jovian escaping relativistic electrons, measurements of interplanetary dust, test of the general relativity around solar conjunctions, observation of the cosmological radio background, and an asteroid flyby (to be further studied). 4. JUICE teams activities during the cruise phase The JUICE teams (mission operation center, science operations center, instrument teams, science working team, working groups, project scientist and mission manager) will be busy with numerous activities. A non-exhaustive list is given below: Spacecraft navigation and operations in the inner solar system, including planetary flybys and payload checkouts; Decision about an asteroid flyby (shortly after launch); Analysis of the cruise data, instrument calibration, scientific analysis, publication and archive; Refinement and agreement (three years before Jupiter orbit insertion) on the trajectory within the Jupiter system; Preparation of the science planning of the nominal mission and of the science analysis of the future data; Studying and preparing the coordination with ground-based and space observatories; Publication of a special issue with mission, instruments and science articles; Recruitment of guest investigators and of potentially additional interdisciplinary scientists; Continue the fruitful collaboration with the NASA Clipper teams. Conclusions The JUICE cruise phase, despite its long duration (9 years), will be busy with many activities, with the goal of being fully ready to start the scientific observations from early 2031 onwards. Figures Figure 1: Evolution of distances (in AU) between the Sun, the Earth, Jupiter and JUICE as a function of time. Figure 2: Overall cruise projected in the ecliptic frame Figure 3: Lunar-Earth flyby in 2023 Figure 4: Illustration of the 300 km lunar flyby in 2023. The lunar and Earth disks are dark due the Sun position.

The elongated crater population on Mars is of great interest in planetary sciences [1]. In 1982, 1988 and 2000 three datasets were established using Viking images [1,2,3]. In 2011 a new and improved set of data with 261 craters and a database including up-to-date images taken by the High Resolution Stereo Camera (HRSC) onboard ESA’s Mars Express were established [4] and continuously updated [5]. Based on the crater shape [6] and the ejecta deposit [7] the direction of impact can be estimated. Since this is not always a straightforward determination, it was decided to check whether the topographic profile could help in ambiguous cases. 1. Introduction Impact cratering is one of the fundamental processes in shaping the surface of terrestrial planets. Even though most impact structures have a circular shape, a small fraction of elongated craters formed by oblique impacts can be observed. Using the recently developed Mars Express database, the current study focuses on the impact direction of elongated craters on Mars. 2. Motivation for the study One major driver for conducting this study is the ongoing discussion of the decaying moonlets hypothesis, which might be an explanation for at least a fraction of the elongated crater population on Mars, as well as the unsolved origin of the Martian moons, Phobos and Deimos [5,9]. 3. Direction of impact As a precondition the crater orientation is analysed and a strong correlation to the crater age can be stated. For the identification of the impact direction a two-stage process is applied and this presentation shows the usefulness of the procedure. A first estimation is based on the crater shape [6] and the ejecta deposit [7]. Figure 1 shows a crater example and table 1 the summarized results for the elongated crater population on Mars. Subsequently, the estimation is reviewed by an analysis of the topographic crater profiles, which result from the pressure distribution during impact [8]. Figure 2 presents the corresponding profile for the first example crater. This review process indicates the validation of the results of the first stage. For craters with morphological characteristics not allowing a distinct identification of the impact direction in stage one this approach helps to improve the dataset dramatically (figures 3 and 4). 4. Figures Figure 1: Estimation of impact direction based on crater shape and ejecta deposit for example crater 1 Figure 2: Altitude profile of example 1 based on HRSC MOLA blended DEM (200m) confirms East to West impact direction Figure 3: Distinct identification of impact direction based on crater shape and ejecta deposit difficult for example crater 2 Figure 4: Altitude profile indicates West to East impact direction 5. Table Table 1: Direction of impact Acknowledgements B. Buchenberger sincerely thanks O. Witasse for more than a decade of great cooperation and friendship that gave him the opportunity to work on such wonderful topics like this. References [1] Schultz, P. H. and Lutz-Garihan, A. B.: Grazing Impacts on Mars: A Record of Lost Satellites, Journal of Geophysical Research, Vol. 87, p. 84-96, 1982. [2] Barlow, N. G.: Crater Size-Frequency Distributions and a Revised Martian Relative Chronology, Icarus, Vol. 75, p. 285-305, 1988. [3] Bottke, W. F., Love, S. G. et al.: Interpreting the Elliptical Crater Populations on Mars, Venus and the Moon, Icarus, Vol. 145, p. 108-121, 2000. [4] Buchenberger, B., Witasse, O. et al.: Elongated craters on Mars revisited: Test of the decaying moonlets hypothesis? EPSC-DPS Joint Meeting, p. 738, 2011. [5] Sefton-Nash, E., Faes, Z. et al.: The Orbit Planes of Impactors that Formed Elongated Martian Craters, EPSC, p.286, 2017. [6] Burchell, M.J., Robin-Williams, R. et al.: The SMART-1 lunar impact, Icarus, Vol. 207, p. 28-38, 2010. [7] Melosh, H.J.: Impact Cratering - A Geologic Process, Oxford University Press, New York, p. 101, 1996. [8] Pierazzo, E. and Melosh, H. J.: Melt Production in Oblique Impacts, Icarus, Vol. 145, p. 252-261, 2000. [9] Craddock, R.A.: Are Phobos and Deimos the result of a giant impact? Icarus, Vol. 211, Iss. 2, p. 1150, 2011.

We present the first long-term characterization of the lower ionosphere of Mars, a region previously inaccessible to orbital observations, based on an analysis of radar echo blackouts observed by MARSIS on Mars Express and SHARAD on the Mars Reconnaissance Orbiter from 2006 to 2017. A blackout occurs when the expected surface reflection is partly to fully attenuated for portions of an observation. Enhanced ionization at altitudes of 60 to 90 km, below the main ionospheric electron density peak, results in the absorption of the radar signal, leading to a radar blackout. MARSIS, operating at frequencies between 1.8 and 5 MHz suffered more blackouts than SHARAD, which has a higher carrier frequency (20 MHz). More events are seen during solar maximum while there is no apparent relationship between blackout occurrence and crustal magnetic fields. Blackouts do occur during both nightside and dayside observations, and have an interesting variation with solar zenith angle. Analysis of MAVEN Solar Energetic Particle (SEP) electron counts between 20 and 200 keV during selected events demonstrates that these electrons are responsible for such events, and we investigate the minimum SEP electron fluxes required to ionize the lower atmosphere and produce measurable attenuation. When both radars observe a radar blackout at the same time, the SEP electron fluxes are at their highest. For certain events, we find that the average spectrum responsible for a blackout is particularly enhanced at the higher energy end of the spectrum, i.e. above 70 keV . This study is, therefore, important for future communications for human exploration of Mars.

The exploration of Callisto is part of the extensive interest in the icy moons characterization. Indeed, Callisto is the Galilean moon with the best-preserved records of the Jovian system formation. Led by the National Space Science Center (NSSC), Chinese Academy of Science (CAS), the planned Gan De mission aims to send an orbiter around Callisto in order to characterize its surface and interior. Potential orbit configurations are currently under study for the Gan De mission proposal.As part of a global characterization of Callisto, its gravity field can be inferred using radio tracking data from an orbiter. Mission characteristics such as orbit type, Earth beta angle and solar elongation will have a direct influence on the recoverability of its gravity field parameters. In this study, we will analyse this influence from closed-loop simulations using the planetary extension of the Bernese GNSS Softwareai.A number of reference orbits with different orbital characteristics will be selected for the Gan De mission and, using an extended force model, will be propagated from different starting dates and different initial Earth beta angles. Realistic Doppler tracking data (2-way X-band Doppler range rate) will be simulated as measurements from ground stations, with a dedicated noise model. These observations will then be used to reconstruct the orbit along with dynamical parameters. The focus of this presentation will be on the quality of the retrieved gravity field parameters and tidal Love number k2.

We study the interaction of three solar wind structures, two stream interaction regions and one interplanetary coronal mass ejection, with Mars' plasma environment during 20-27 November 2007. This period corresponds to the solar minimum between the solar cycles 23 and 24 which was characterized by very low values of the solar wind density and dynamic pressure and low IMF magnitude. During that time the Mars-Express orbit was in the terminator plane, while the Earth, Sun, and Mars were almost aligned, so we use the ACE and STEREO probes as solar wind monitors in order to identify and characterize the structures that later hit Mars. We find that the passage of these structures caused strong variations of in the bow shock location (between 2.2 and 3.0~R$_M$), compression of the magnetospheric cavity (up to 45~\%) and an increased transterminator flow below 2~R$_M$ (by a factor of $\leq$8). This study shows that during times of low solar activity, modest space weather phenomena may cause large variations of plasma flow at Mars., Comment: Published in Journal of Geophysical Research

This is an open access article under the CC BY-NC-ND license., This work uses a subset of “quiet” MaRS ionospheric dayside observations (MaRSquiet, 2004–2017) and a 1-D photochemical model (IonA-2) to investigate the potential formation processes of the excess electron densities merged with the base of the main ionosphere (Mm). 42% of the investigated MaRS observations contain identified Mm, which occur in a large variety of shapes ranging from smoothly decreasing electron densities to peak structures below the base of M1. The Mm appear over the full range of accessible solar zenith angles (50° - 90°) and are found between approximately 70 and 110 km altitude. Their base is found on average deeper in the atmosphere than the base of the averaged undisturbed MaRS electron density profiles. This indicates a dependence of the Mm formation on energy sources that penetrate deep into the atmosphere. This is supported by a strong positive correlation with increasing solar activity when solar flares, coronal mass ejections, and enhanced short solar X-ray and Ly-α intensities are more common. No relationship is found between the Mm occurrence rate and the magnitude/inclination of the weak crustal crustal magnetic field in MaRSquiet. Investigations with the IonA-2 photochemical model for undisturbed and flare conditions show that the ionization of the local neutral atmosphere by solar X-ray radiation, The Mars Express Radio Science Experiment (MaRS) is funded by the German Space Agency (DLR) under the Grant 50QM1802. Support for Mars Express Radio Science at Stanford University is provided by NASA through a JPL Contract. Support for the Multimission Radio Science Support Team is provided by NASA/JPL. Portions of this research were performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with NASA. We thank everyone involved in the Mars Express project at ESTEC, ESOC, ESAC, JPL, and the ESTRACK and DSN ground stations for their continuous support. K. P. and M. P. acknowledge funding for this project by the Deutsche Forschungsgemeinschaft (DFG) under Grant PA 525/11-1, PA525/11-2 and PA 525/14-1. F.G.G. is funded by the Spanish Ministerio de Ciencia, Innovacion y Universidades, the Agencia Estatal de Investigacion and EC FEDER funds under project RTI2018-100920-J-I00, and acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709). Solar Irradiance Platform historical irradiances are provided courtesy of W. Kent Tobiska and Space Environment Technologies. These historical irradiances have been developed with partial funding from the NASA UARS, TIMED, and SOHO missions. We acknowledge support for work conducted on the development of the Mars Climate Database from the European Space Agency (under ESTEC Contract 11369/95/NL/JG(SC)) and from CNES. CNRS (LMD group), the IAA and the UK Particle Physics and Astronomy Research Council (AOPP, Oxford Group) also provided support during the development of the Martian General Circulation Models.

The comparative study of planetary systems is a unique source of new scientific insight: following the six “key science questions” of the “Planetary Exploration, Horizon 2061” long-term foresight exercise, it can reveal to us the diversity of their objects (Question 1) and of their architectures (Question 2), help us better understand their origins (Question 3) and how they work (Question 4), find and characterize habitable worlds (Question 5), and ultimately, search for alien life (Question 6). But a huge “knowledge gap” exists which limits the applicability of this approach in the solar system itself: two of its secondary planetary systems, the ice giant systems of Uranus and Neptune, remain poorly explored. Starting from an analysis of our current limited knowledge of solar system ice giants and their systems in the light of these six key science questions, we show that a long-term plan for the space exploration of ice giants and their systems will greatly contribute to answer these questions. To do so, we identify the key measurements needed to address each of these questions, the destinations to choose (Uranus, Neptune, Triton or a subset of them), the combinations of space platform(s) and the types of flight sequences needed. We then examine the different launch windows available until 2061, using a Jupiter fly-by, to send a mission to Uranus or Neptune, and find that: (1) an optimized choice of platforms and flight sequences makes it possible to address a broad range of the key science questions with one mission at one of the planets. Combining an atmospheric entry probe with an orbiter tour starting on a high-inclination, low periapse orbit, followed by a sequence of lower inclination orbits (or the other way around) appears to be an optimal choice. (2) a combination of two missions to each of the ice giant systems, to be flown in parallel or in sequence, will address five out of the six key questions and establish the prerequisites to address the sixth one: searching for life at one of the most promising Ice Giant moons. (3) The 2032 Jupiter fly-by window, which offers a unique opportunity to implement this plan, should be considered in priority; if this window cannot be met, using the 2036 Jupiter fly-by window to send a mission to Uranus first, and then the 2045 window for a mission to Neptune, will allow one to achieve the same objectives; as a back-up option, one should consider an orbiter + probe mission to one of the planets and a close fly-by of the other planet to deliver a probe into its atmosphere, using the opportunity of a future mission on its way to Kuiper Belt Objects or the interstellar medium; (4) based on the examination of the habitability of the different moons by the first two missions, a third one can be properly designed to search for life at the most promising moon, likely Triton, or one of the active moons of Uranus. Thus, by 2061 the first two missions of this plan can be implemented and a third mission focusing on the search for life can be designed. Given that such a plan may be out of reach of a single national agency, international collaboration is the most promising way to implement it.

We present an analysis of radar blackouts observed by MARSIS on Mars Express and SHARAD on Mars Reconnaissance Orbiter for the interval 2006 – 2017. The period of interest encompasses the extended solar minimum between solar cycles 23 and 24 as well as the solar maximum of cycle 24. Blackouts have been identified by eye through scanning daily plots of the surface reflection for both radars. A blackout occurs when, for no apparent instrumental reason, the surface reflection normally expected is either not observed (total) or when the surface reflection is seen for only part of the orbit or the surface reflection is both weaker and spread over a significant time delay (partial). Such blackouts are caused by enhanced ionisation at altitudes below the main ionospheric electron density peak resulting in increased absorption of the radar signal. There are more occurrences observed by MARSIS than SHARAD, which is expected due to the lower absorption at the higher operating frequency of SHARAD. We also observe more blackouts during solar maximum than solar minimum. Indeed, there are no total blackouts during the extended solar minimum, although both radars do have partial blackouts. There is no apparent relationship between blackout occurrence and crustal magnetic fields. Following previous work, which has indicated that solar energetic particles, specifically electrons are responsible for the enhanced ionisation in the atmosphere, we also present the analysis of the MAVEN SEP electrons between 20 keV and 2 MeV during events when all three spacecraft were operational. We find that the SEP electron flux-energy relationship is much enhanced during the total blackouts, in particular where both radars are impacted, while for partial blackouts the flux-energy spectrum is closer to those from orbits where no blackout occurs. We also find that for certain events, the average spectrum which result in a blackout is particularly enhanced at the higher energy end of the spectrum, above 50 keV. The average spectra from each condition is presented. We conclude that there is a higher probability of a radar blackout during solar maximum, that crustal magnetic fields play no apparent role in the their observational occurrence, that the higher energy (< 50 keV) electrons are responsible, and that for events where both radars observe a radar blackout the SEP electron fluxes are at their highest.

Figure 1: MEX-MaRS X-band observations of the dayside ionosphere of Mars for (a) Day of Year (DoY) 343 (2005) and (b) DoY 215 (2014). Combined X- and S-band (differential Doppler) observations for (c) DoY 011 (2014) and (d) DoY 006 (2006). The gray dashed line indicates the noise level, while the black dashed line marks the lowest valid altitude of the individual observation (details about the parameter derivation in [2]).The Mars Express Radio Science experiment (MaRS) on board the Mars Express spacecraft has observed the Mars atmosphere and ionosphere since 2004. More than 900 high-resolution MaRS height profiles of the ionospheric electron density from the topside down to the ionospheric base are available.The two dominant features of the undisturbed Martian dayside ionosphere are the main peak (M2), caused mainly by solar radiation in the Extreme Ultraviolet, and the secondary layer (M1), mostly formed by primary and secondary impact ionization of short solar X-rays < 10 nm [1]. The region below the M1 peak is highly variable and regularly contains merged excess electron density regions (Mm) in various shapes [2] (Figures 1).More than 15 years of MaRS radio science observations are used to study the behavior of the lowest region of the Martian dayside ionosphere. Categories for the identified Mm shapes are defined and statistics of the individual Mm shape occurrences are provided. The 1-D photochemical model IonA-2 (Ionization in Atmospheres 2 [2]) is applied to investigate which of the identified Mm shapes can be reproduced by solar radiation of the quiet Sun and under solar M- and X-flare conditions. References [1] Fox J. L. et al. (1996), Adv. Space Res., 17, 11, 203-218. [2] Peter K. (2018), PhD Dissertation, https://kups.ub.uni-koeln.de/8110/.

Many studies were carried out recently regarding the exploration of Ice Giants, in the context of the next NASA decadal survey in planetary sciences and astrobiology, of the next planning cycle in ESA's Science Programme, and of a possible NASA-ESA collaboration. A mission to an Ice Giant could include an atmospheric probe, to operate in the 1-10 bars pressure range. Its payload could comprise sensor(s) devoted to the measurement of electrical properties, plasma densities and conductivities. In order to check the performances of such instruments, it is necessary to develop models of the electron and ion densities profiles, with and without aerosols, from which the electrical conductivities can be derived. A model was developed based on studies performed at Mars and Titan [1-2], which computes the atmospheric positive and negative electrical conductivities between 0.1 and 15 bars in the atmosphere of Neptune and Uranus. In this altitude range, galactic cosmic rays ionize the atmospheric constituents, which react with atmospheric neutrals and aerosols, leading to the formation of ions heavier than the ones produced by cosmic rays. The densities of positive ions, electrons and charged aerosols are obtained by solving their corresponding continuity equations. It has been found that aerosol particles tend to be negatively charged due to the attachment of electrons, as a more efficient process than the attachment of positive ions. Therefore, the electrical conductivity due to negative charges is strongly reduced compared to the one expected when aerosols are not present. However, the electrical conductivity due to positive ions does not change so dramatically. The experimental determination of both components of the electrical conductivity can be useful to understand the properties of aerosols, plasma and electric currents in the atmospheres of Ice Giants. Figure 1 and 2 shows some the first results of the number density and electrical conductivities in the atmospheres of Uranus and Neptune. They were calculated for a cosmic rays flux valid for a heliocentric potential of 100 MV, neglecting the planetary internal magnetic field, a mean ion mass of 100 amu and the aerosol particle distribution reported by Toledo et al. [3-4], which is extended down to the pressure range here considered. References [1] Cardnell, S., et al. (2016), A photochemical model of the dust-loaded ionosphere of Mars, J. Geophys. Res. Planets, 121, doi:10.1002/2016JE005077. [2] Molina-Cuberos, G.J., et al. (2018) Aerosols: The key to understanding Titan's lower ionosphere, Planet. Space Sci, 153, 157 – 162, doi: 10.1016/j.pss.2018.02.007. [3] Toledo et al. (2019), Constraints on Uranus's haze structure, formation and transport, Icarus 0019-1035, doi: 10.1016/j.icarus.2019.05.018 [4] Toledo et al. (2020) Constraints on Neptune’s haze structure and formation from VLT observations in the H-band, Icarus, doi: 10.1016/j.icarus.2020.113808

Radio Occultation is a very powerful technique to probe a planetary atmosphere, in providing vertical density profiles of the neutral atmosphere and ionosphere. The standard method uses a radio link at S and/or X band between a spacecraft and an Earth ground station. At Mars, such measurements are conducted since the 60s. The three most recent data sets are from MGS (1998-2006), Mars Express (since 2004) and MAVEN (since 2016). Taking advantage of two European spacecraft in orbit around Mars, the European Space Agency is currently preparing an experiment that consists of mutual radio occultations between Mars Express and the ExoMars Trace Gas Orbiter. Both spacecraft use UHF transceivers that are included primarily for communication between landers on the surface of Mars and the spacecraft, where the spacecraft act as relay orbiters to pass the data from the landers on to Earth. Therefore, these mutual occultations will be performed in the UHF range (centered around a frequency of 400 MHz). The feasibility of this technique on UHF was demonstrated between the NASA Mars Odyssey and Mars Reconnaissance Orbiters [Ao et al., 2015].In this presentation, the advantages and challenges of this technique over the traditional spacecraft to Earth occultation measurements, the plans for conducting these experiments with Mars Express and the Trace Gas Orbiter, and the envisaged data processing technique will be briefly reviewed.Before the data becomes available, and in order to prepare the data processing, a simulation-based strategy has been adopted to implement an algorithm able to retrieve vertical electron density profiles from Doppler shift measurements. More specifically, as a first step, simulated spacecraft orbits are calculated and a Chapman function is used to obtain the electron density of the Martian ionosphere. Subsequently, a numerical 3D ray-tracing algorithm [Kashcheyev et al., 2012] is applied to compute ray trajectories in the presence of the ionosphere and the relevant Doppler shift time series corresponding to the simulated radio occultation event. Then, assuming a spherical symmetry [Fjeldbo et al., 1971] for the ionosphere electron density, the (excess) Doppler data are converted to bending angles and impact parameters. Finally, the bending angle profile is inverted (through Abel integral) to a vertical refractivity profile, which, in turn, provides information about the ionospheric electron density.For completeness, the simulation described above has been carried out with an exponential refractivity function defining the neutral atmosphere alone and with both the Chapman and the exponential refractivity functions to simulate the whole atmosphere of Mars.The first results obtained by means of the mentioned approaches will be presented, with particular focus on the retrieval of the ionospheric electron density profiles.ReferencesAo, C. O., C. D. Edwards Jr., D. S. Kahan, X. Pi, S. W. Asmar, and A. J. Mannucci (2015), A first demonstration of Mars crosslink occultation measurements, Radio Sci., 50, 997–1007, doi:10.1002/2015RS005750.Fjeldbo, G., A. J. Kliore, and V. R. Eshleman (1971), The neutral atmosphere of Venus as studied with the Mariner V radio occultation experiments, Astron. J., 76, 123–140.Kashcheyev, A., B. Nava, and S. M. Radicella (2012), Estimation of higher-order ionospheric errors in GNSS positioning using a realistic 3-D electron density model, Radio Sci., 47, RS4008, doi:10.1029/2011RS004976

Surveying potential cruise fly-by opportunities for an Ice Giant mission Marc Costa Sitjà1, Olivier Witasse2, Alfredo Escalante López1 1RHEA for European Sapce Agency,2European Space Agency Abstract We present a systematic approach to analyse rapidly fly-by opportunities for the cruise phase of a mission to an Ice Giant. Such flyby would provide a unique opportunities to characterise Jupiter Trojans, Centaurs, or Jupiter Family comets. A Mission to the Ice Giants A mission to an Ice Giant (Neptune and/or Uranus) will be among the ones examined by NASA's next Planetary Sciences and Astrobiology Decadal survey. ESA was exploring in 2018-2019 a potential collaboration to a NASA-led mission to an ice giant and has carried out a concurrent engineering design study [1] for possible European contributions. In this study, a dual launch in 2031 was contemplated; after a Jupiter swingby in late 2032, one orbiter would go to Uranus while the second one would reach Neptune. The long cruise of a mission to Uranus and or Neptune would provide an excellent opportunity scientific investigations like heliophysics science [2], [3], [4]. In addition, it could provide an unexpected chance to visit an unexplored small body. Cruise fly-by opportunities Examples of such flybys by missions to the outer solar system are well known. To mention some, the Rosetta spacecraft performed two flyb-bys of asteroid, 2867 Steins and 21 Lutetia [5]; Galileo performed fly-bys of 951 Gaspra and 243 Ida (these images provided the first direct confirmation of an asteroid moon, Dactyl) [6] and Cassini-Huygens performed a more humble fly-by of 2685 Masursky at about 0.011 AU. In general flyby targets can only be chosen after launch from a list of candidates according to scientific interest, fly-by geometry, operational feasibility and the additional cost of propellant for the trajectory modifications [7]. The expected results from such observations include: the rotational properties of the target including the astrometric refinement of their orbit, the determination of their spin state and pole direction, global characteristics such as shape, volume, mass and bulk density, surface physical properties and morphology, detailed chemical and mineralogical characterization, effects of the space weathering on surface properties due to the solar wind interactions and exploration of the target's environment and activity. Mining fly-by opportunities We took a cruise trajectory to Neptune used in ESA's CDF study to search for a candidate flyby, as a check whether the science return of such mission could be enhanced. In this study, we checked whether a quick assessment of flyby opportunities for a candidate trajectory was possible. In our analysis, we considered to search for JupiterTrojans, Centaurs, TransNeptunian Objects, and Jupiter-Family Comets [8]. The description provided for each family (sorted by orbit type) is the following: JupiterTrojans (T): Asteroids trapped in Jupiter's L4/L5 Lagrange points (4.6 AU < a < 5.5 AU; e < 0.3). Centaurs (C): Objects with orbits between Jupiter and Neptune (5.5 AU < a < 30.1 AU). TransNeptunian Objects (TNO): Objects with orbits outside Neptune (a > 30.1 AU). JupiterFamily Comets (JFC): As defined either by Levison and Duncan (2 < TJupiter < 3) or by the classical definition (P < 20 y). For a preliminary assessment, we decided to use data from the JPL Small-Body Database Search Engine [9]. From the database we selected a total of 12507 bodies for which we retrieved the data in SPICE format (Spacecraft Kernel) [10]. To do so systematically, we used a Julia based client wrapper to Horizons [11] and then we took advantage of the SPICE Toolkit capabilities to perform a Closest Approach (CA) search for each body and obtain the time and distance of the event. We present preliminary results of our study hereby. First results The results provide us with some interesting figures. The histogram below - table and in Figure 1- provides a wider view of the resulting distribution of objects as a function of the CA distance. Distance Bin (AU) 0-0.1 0.1-0.5 0.5-1.0 1.0-2.0 2.0-100.0 Number of objects 1 7 12 42 12444 We selected some examples that are provided in the following table: Body Name Family Body ID Inclination (deg) CA (AU) Shoemaker-Levy 9 JFC 1000183 5.982 0.16 335P/Gibbs JFC 1003007 7.27 0.07 P/2015 TP200 JFC 1003474 8.77 0.38 2013 CT160 C 3667711 16.76 0.46 2019 TP13 C 3985102 4.93 0.44 The ongoing analysis shows that there is only one interesting result for the current trajectory: comet 335P/Gibbs. Such flyby could only be compared with the before mentioned Cassini 2685 Masursky at about 0.011 AU, in such case we would be seven times further and with such a rapid scenario we could already identify a potential flyby. Figure 2 shows a simulation of a theoretical Ice Giants flyby with 335P/Gibbs. We repeat that this report is a very preliminary and approximate result, an updated will be given at the time of the conference. The main purpose of this contribution was to prove that such studies are feasible and can later help to optimise the trajectory design and the target selection process for fly-by opportunities. We plan to conduct such search with other mission such as JUICE and also to expand the catalogue of bodies for which we will conduct such searches. References [1] P. F. S. Bayon, Cdf study report: Ice giants (2019). [2] L. N. Fletcher, Ice giant system exploration, white paper response to75esa call for voyage 2040 science themes (2019). [3] C. Arridge, et. al., The science case for an orbital mission to uranus: Exploring the origins and evolution of ice giant planets, Planetary and Space Science 104 (2014) 122 – 140 [4] T. Bocanegra-Bahamon, et. al., Muse mission to the uranian system: Unveiling the evolution and formation85of ice giants, Advances in Space Research 55 (2015) 2190 – 2216 [5] M. Barucci, M. Fulchignoni, A. Rossi,Rosetta asteroid targets:892867 steins and 21 lutetia, Space Science Reviews 128 (2007) 67–78. [6] M. J. Belton, C. R. Chapman, et.atl., Galileo’s encounter with 243 ida:An overview of94the imaging experiment, Icarus 120 (1996) 1 – 19 [7] F. B. T. Morley, Rosetta navigation for the fly-by of asteroid 2867 steins98(2009). [8] B. Gladman, B. Marsden, C. Vanlaerhoven, Nomenclature in the outer solar system, The Solar System Beyond Neptune (2008) [9] J. Giorgini, et.al., JP:’s on-line solar system data service [10] C.H.Acton, Ancillary datas ervices of nasa's navigation and ancillary information facility, Planeary and Space Science 44 (1996) 65–70. [11] J. A. Perez-Hernandez, An interface to nasa-jpl horizons system in julia

Thermal properties of frozen salt solutions are crucial to interpret the JUpiter ICy moons Explorer (JUICE) (ESA) and Europa Clipper (NASA) missions, which will be launched in the upcoming years to make detailed observations of the giant gaseous planet Jupiter and three of its largest moons (Ganymede, Callisto, and Europa) due to the scarcity of experimental measurements. Therefore, we have conducted a set of experiments to measure and study the thermal conductivity and calorimetry of macroscopic frozen salt solutions of particular interest in these regions, including Na-chloride (NaCl), Mg-sulphate (MgSO4), sodium sulphate (Na2SO4), and Magnesium chloride (MgCl2). A climatic chamber has been used to mimic the cryogenic conditions in the Jovian Icy Moons. Measurements were performed at atmospheric pressure and temperatures from 0 to -70ºC. Temperature and thermal conductivity were measured during the course of the experiments. A side effect of these measurements is that they served to spot phase changes in the ice mixtures. A small sample of the liquid salt-water solution was set aside for the calorimetry measurements. These experiments and the measurements of thermal conductivity and calorimetry will be valuable to constrain the chemical composition, physical state, and temperature of the upper layers of the icy crusts of Ganymede, Callisto, and Europa (please see abstracts EPSC Muñoz Iglesias et al. 2020 and EPSC Solomonidou et al. 2020).

The comparative study of the different planetary systems accessible to our observations is a unique source of new scientific insight: it can reveal to us the diversity of these systems and of the objects within them, help us better understand their origins and how they work, find and characterize habitable worlds, and ultimately, search for alien life in our galactic neighborhood. But, in the solar system itself, two of its secondary planetary systems, the ice giant systems, as well as their two main objects, Uranus and Neptune, remain poorly explored. We will present an analysis of our current limited knowledge of these systems in the light of six key science questions about planetary systems formulated in the “Planetary Exploration, Horizon 2061” long-term foresight exercise: (Q1) What is the diversity of planetary systems objects? (Q2) What is the diversity of their architectures? (Q3) What do we know of their origins and formation scenarios? (Q4) How do they work? (Q5) Do they host potential habitats? (Q6) Where and how to search for life? We will show that a long-term plan for the space exploration of ice giants and their systems, complemented by the combination of Earth and space-based observations, will provide major contributions to answers to these six questions. In order to do so, we identify the measurements that must be performed in priority to address each of these questions, the destinations to choose (Uranus, Neptune, Triton or a subset of them), and the combinations of space platform(s) (orbiter, atmospheric entry probe(s), lander…) and of flight sequences needed. Based on this analysis, we look at the different launch windows available until 2061, using a Jupiter fly-by, to send a mission to Uranus or Neptune and find that: (1) a single mission to one of the Ice giants, combining an atmospheric entry probe and an orbiter tour starting on a high-inclination, low-periapse orbit, followed by a sequence of lower- inclination orbits, at least at one of the planets, will make it possible to address a broad range of these key questions; (2) a combination of two well-designed missions to each of the ice giant systems, to be flown in parallel or in sequence, will make it possible to address five out of the six key questions, and to establish the prerequisites for addressing the sixth one. The 2032 Jupiter fly-by window offers a unique opportunity to achieve this goal; (3) if this window cannot be met, using the 2036 Jupiter fly-by window to send a mission to Uranus first, and then the 2045 window for a mission to Neptune, will achieve the same goals. As a back-up option, the feasibility of sending an orbiter + probe mission to one of the planets and using the opportunity of a mission on its way to the interstellar medium to execute a close fly-by of the other planet and deliver a probe into its atmosphere should be studied carefully; (4) based on the expected science return of the first two missions, a third mission focusing on the search for life at a promising moon, namely Triton based on our current knowledge, or perhaps one of the active moons of Uranus after due characterization, can be properly designed. By the 2061 horizon, the first two missions of this plan can be implemented and the design of a third mission focusing on the search for life can be consolidated. Given the likelihood that such a plan may be out of reach of a single national agency, international collaboration is the most promising way to implement it.

In the coming years The JUpiter ICy moons Explorer (JUICE) (ESA) and Europa Clipper (NASA) missions will study the icy crusts of the main Galilean moons of Jupiter. They will use the penetrating radars RIME and REASON, which will work at wave frequency ranges able to penetrate up to 9 and 30 Km depth respectively, in combination with other instruments [Bruzzone et al. 2013, Aglyamov et al. 2017]. In this regard, we have started a set of experiments to study the electrical properties of materials at low temperatures with the aim to help with the interpretation obtained from the level of attenuation of the radar waves. Ultimately, they will be useful to constrain the chemical composition, physical state and temperature of the upper layers of the icy crusts of Ganymede, Callisto and Europa (please see abstracts EPSC González Díaz et al. 2020 and EPSC Solomonidou et al. 2020). The first set of experiments have been done in a high-pressure chamber equipped with pressure and temperature sensors in direct contact with the sample and a large sapphire window which allows textural and spectroscopic analyses. We have characterized aqueous solutions with salts (MgSO4, NaCl, MgCl2, Mg(ClO4)2, Na2CO3), volatiles (CO2) and clays (nontronite, montmorillonite) at temperatures down to 223 K and pressures up to 60 MPa. Samples were studied by pressure-temperature (P-T) cycles in two ways: (a) first freezing the solution and pressurizing it (TPPT method) and (b) first pressurizing the solution and then freezing it (PTTP method), in order to examine textural and grain size heterogeneities and fracture formation depending on the method of formation. The cooling of the samples led to the final formation of water ice, hydrated salts and clathrate hydrates. Raman spectroscopy was used to control the mineral assemblages and understand better the crust environments and processes that can explain the resulting values, like the appearance of supercooled brines, amorphous phases and recrystallizations during the P-T cycles. We measured the dielectric properties of these samples with a BDS80 Broadband Dielectric Spectroscopy system (Novocontrol) which allows to work in a frequency range from 1 Hz to 10 MHz and temperatures from 143 to 323 K. Both permittivity and electric conductivity were measured at 0.1 MPa while cooling the samples in temperature steps of 10 K. From these data we estimated, on the one hand, the activation energy for motion of the electric charges of each solution, and on the other hand, the attenuation of the radar wave depending on the chemical composition and the temperature of the sample, and the frequency of the electric field applied [Pettinelli et al. 2015]. The already obtained novel data will be used as reference for a second set of experiments, consisting on the same dielectric properties’ characterization but, in this set, samples will be also subjected to high pressure conditions. References Aglyamov et al. (2017) Bright prospects for radar detection of Europa’s ocean, Icarus, 281, 334-337. Bruzzone et al. (2013) RIME: Radar for Icy moon Exploration, IEEE International Geoscience and Remote Sensing Symposium - IGARSS, Melbourne, 3907-3910. Pettinelli et al. (2015) Dielectric properties of Jovian satellite ice analogs for subsurface radar exploration: A review, Reviews of Geophysics, 53, 593-641.

We use Spacecraft Plasma Interaction Software (SPIS) simulations of the surface charging of the Jupiter Icy Moons Explorer (JUICE) spacecraft to study how the variable magnetospheric environment of Jupiter will impact the future JUICE particle and electric field measurements. The study has been limited to the magnetospheric region relevant for JUICE, that is, the environments of the inner and middle magnetosphere of Jupiter. The closest approach of Jupiter will be at 9.3 RJ. In the inner magnetosphere the spacecraft will charge a few volts negative for the typical plasma sheet environment, where ne,cold ≈ 50 cm-3 and Te,cold ≈ 20 eV. However, Galileo detected plasma densities of up to 600 cm-3 in the region around 9.4 RJ (Kurth et al., 2001). These densities could be due to activity on Europa, such as plumes, or a local disturbance of cold and dense iogenic plasma (Bagenal et al., 2015). Such high densities could result in surface potentials of tens of volts, when assuming Te,cold ≈ 5 eV, which would inhibit cold electron measurements performed by the electron spectrometer of JUICE, since the electrons would be repelled before reaching the detector. In addition, the large differential charging of tens of volts, due to the dielectric surfaces, would disturb electric field measurements. However, the cold electron temperature is not well constrained for this particular disturbance and a lower plasma temperatures would decrease the magnitude of the surface potential. Our SPIS simulations show surface potentials of a few volts positive for typical magnetospheric environments in the plasma sheet between 15 and 26 RJ, where ne,cold > 20 ne,hot and the hot electron component range from 1-5 keV. However, Galileo measurements occasionally show hot electron densities equal to or slightly larger than the typical cold electron densities (Futaana et al., 2018). Simulated surface potentials, using ne,cold ≈ ne,hot, show no significant difference compared to the typical environment since the increase in hot electrons is counterbalanced by the increase in the production of secondary electrons. In this particular environment, higher electron densities will charge the spacecraft more negative while higher secondary electron production will charge the spacecraft more positive. Assuming Maxwellian distributions, we obtain that an unusually dense hot, 1-5 keV, electron component, like the one measured by Galileo, would not disturb the particle measurements of JUICE. Our study shows that the absolute charging of the spacecraft strongly depends on the cold electron density and temperature, and, for certain environments, on the spacecraft orientation relative to the plasma flow and the solar radiation. An unusually dense and hot, 1-5 keV, electron plasma component will not have a substantial impact on the charging, in the studied region. We are investigating whether different energy distributons will change this conclusion. The SPIS JUICE surface charging simulation results show that only minor perturbations will be obtained in typical Jovian magnetospheric environments, while substantial perturbations will occasionally occur in the disturbed magnetosphere.

Planetary Space Weather is the discipline that studies the state of the Sun and how it interacts with the interplanetary and planetary environments. It is driven by the Sun’s activity, particularly through large eruptions of plasma (known as coronal mass ejections, CMEs), solar wind stream interaction regions (SIR) formed by the interaction of high-speed solar wind streams with the preceding slower solar wind, and bursts of solar energetic particles (SEPs) that form radiation storms. This is an emerging topic, whose real-time forecast is very challenging because among other factors, it needs a continuous coverage of its variability within the whole heliosphere as well as of the Sun’s activity to improve forecasting. The long cruise of BepiColombo constitutes an exceptional opportunity for studying the Space Weather evolution within half-astronomical unit (AU), as well as in certain parts of its journey, can be used as an upstream solar wind monitor for Venus, Mars and even the outer planets. This work will present preliminary results of the Space Weather conditions encountered by BepiColombo since its launch until mid-2020, which includes data from the solar minimum of activity and few slow solar wind structures. Data come from three of its instruments that are operational for most of the cruise phase, i.e., the BepiColombo Radiation Monitor (BERM), the Mercury Planetary Orbiter Magnetometer (MPO-MAG), and the Solar Intensity X-ray and particle Spectrometer (SIXS). Modelling support for the data observations will be also presented with the so-called solar wind ENLIL simulations.

The flux of energetic protons (80 keV-1.04 MeV) near the Galilean moons was measured by the Energetic Particle Detector (EPD) on the Galileo mission (1995 - 2003). Near Galilean moons (such as Io and Europa) depletions of the energetic ion flux, of several orders of magnitude, were observed (see Figure 1). Such energetic ion depletions can be caused by the precipitation of these particles onto the moon’s surface or charge exchange with the neutral atmosphere. In addition, a magnetic field gradient can restrict access of the ions to certain regions, creating a “forbidden region.” To interpret the depletion features in the EPD data, a Monte Carlo particle tracing code has been developed. The expected flux of the energetic ions is simulated under different scenarios including those with and without an atmosphere, plume or inhomogeneous electromagnetic field. By comparing the simulated distribution to the EPD data, the cause of the depletion features can be investigated. We identify the following causes of energetic proton depletions near Europa: Depletions are consistent with plumes during the flybys E12 and E26. These plumes coincide with the source location of Jia et al., 2018 and Arnold et al., 2019. Depletions are consistent with atmospheric charge exchange during the flyby E26 Depletions coincide with Europa’s Alfvén wing during the flybys E17 and E25A. The Alfvén wings are two cylindrical regions extending to the north and south of Europa in which the low-energy plasma and the magnetic field are modified compared to the upstream conditions. Furthermore, we investigate the effect of varying the atmospheric properties (scale height, density, presence of a sputtered component) and plume properties (density, location) on the depletions. Figure 1: Normalized flux of H+ (220 to 550 keV) during the Galileo flybys of Europa. Depletions shown as darker colors.

Abstract In this work, we compare simulation of the precipitating flux for different solar wind dynamic pressure with MAVEN observations. In particular, we focus on the fluxes of precipitating ion towards Mars' atmosphere as seen by MAVEN/SWIA (cs product), an energy and angular ion spectrometer [1]. We also use LatHyS, which is a 3D multispecies parallelized hybrid model that describes the formation of Mars electromagnetic environment induced by its interaction with the solar wind [2]. 1. Introduction Although atmospheric sputtering is a minor component of atmospheric escape today, it is thought to have been much more important four billion years ago [3]. Heavy ion precipitation is the primary driver of atmospheric sputtering. At the present epoch, the efficiency of Mars' atmospheric sputtering by precipitating heavy ions to induce atmospheric escape is expected to be small compared to other mechanisms of atmospheric erosion. However, since the main driver of sputtering is ion precipitation, it is crucial to constrain the dependence of the precipitating ion flux on present solar wind conditions, before any extrapolation to past solar conditions. By comparing simulation results and MAVEN observations, we here investigate the mechanisms controlling the precipitation when the solar wind dynamic pressure change. We will present how the precipitating ion flux, measured by MAVEN/SWIA, is influenced by the solar wind dynamic pressure and will analyze these observations by comparison with simulation results. 2. Observations and simulations results We define two sets of different solar wind dynamic pressure from the set of MAVEN observations of the precipitating flux and simulate Mars’ interaction with the solar wind for the average values of the solar parameters (Extreme Ultraviolet irradiance, Interplanetary magnetic field, solar wind density, solar wind speed...) for both sets. We then reconstruct map of the precipitating heavy ion flux at 250km in altitude and the simulated precipitating flux along each MAVEN trajectory used in our analysis. 3. Summary Comparing MAVEN observations with models improves our understanding of the parameters that control the precipitating ion flux. By defining two sets, characterized by different solar wind dynamic pressure and modelling them, we present the comparison between models and observations. Acknowledgements This work was supported by the DIM ACAV and the ESA/ESTEC faculty. This work was also supported by CNES “Système Solaire” program and by the “Programme National de Planétologie” and “Programme National Soleil-Terre”. This work is also part of HELIOSARES Project supported by the ANR (ANR-09-BLAN-0223), ANR MARMITE (ANR-13-BS05-0012-02) and ANR TEMPETE (ANR-17-CE31-0016). Spacecraft data used in this paper are archived and available in the Planetary Data System Archive (https://pds.nasa.gov/). Numerical simulation results used in this article can be found in the simulation database (http://impex.latmos.ipsl.fr). References [1] Leblanc F., R. Modolo and al. (2015), Geophys. Res. Lett, 42, 9135-9141, doi : 10.1002/2015GL066170. [2] Modolo, R., et al. (2016), J. Geophys. Res. Space Physics, 121, 6378–6399, doi: 10.1002/2015JA022324. [3] Luhmann, J.G., Johnson, R.E., Zhang, M.H.G., (1992), Geophys. Res. Lett., 19, 21, 2151-2154.

ESA’s Mars Exress spacecraft has been exploring the red planet since January 2004. The spacecraft is able to receive and transmit signals at both S-band and X-band. Changes in the radio signals properties while propagating through the atmosphere yield information on the electron density profile. The Mars’ ionosphere is very variable in time. One source of its variability is the solar activity. Here we study the effect of solar flares and coronal mass ejections on the Mars’ ionosphere using the publicly available Mars Express radio occultation data. A new software in python was developed to process the residual frequencies data sets, and was validated using higher-level archival data. We calculate the electron density profiles before, during, and after such solar events. The variations in ionospheric parameters (total electron content, peak density and altitude) are quantified in order to understand the ionospheric changes due to solar activity. As expected, significant variations in these parameters have been identified. The results are compared with additional measurements and models. Figure 1: The snapshots of the solar wind disturbances on 9 June 2011 (left). Electron density profiles observed by MEX (Right)

Solar energetic particles are one of the main sources of particle radiation seen in space. In the first part of September 2017 the most active solar period of cycle 24 produced four large X-class flares and a series of (interplanetary) coronal mass ejections, which gave rise to radiation storms seen over all energies and at the ground by neutron monitors. This paper presents comprehensive cross comparisons of in situ radiation detector data from near-Earth satellites to give an appraisal on the state of present data processing for monitors of such particles. Many of these data sets have been the target of previous cross calibrations, and this event with a hard spectrum provides the opportunity to validate these results. As a result of the excellent agreement found between these data sets and the use of neutron monitor data, this paper also presents an analytical expression for fluence spectrum for the event. Derived ionizing dose values have been computed to show that although there is a significant high-energy component, the event was not particularly concerning as regards dose effects in spacecraft electronics. Several sets of spacecraft data illustrating single event effects are presented showing a more significant impact in this regard. Such a hard event can penetrate thick shielding; human dose quantities measured inside the International Space Station and derived through modeling for aircraft altitudes are also presented. Lastly, simulation results of coronal mass ejection propagation through the heliosphere are presented along with data from Mars-orbiting spacecraft in addition to data from the Mars surface.