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Atomic hydrogen and oxygen are the dominant species in the Martian exosphere. Atomic hydrogen is essentially produced from the dissociation of H2O, whereas, hot oxygen atoms are populated by non-thermal processes such as the dissociative recombination of O2+ with electrons in the Martian ionosphere. The study of these species helps to understand the evolution of the Martian atmosphere and more specifically the history of water on Mars. The Emirates Mars Ultraviolet Spectrometer (EMUS), one of the primary instruments onboard the Emirates Mars Mission (EMM), has been observing atomic hydrogen and oxygen in the Martian exosphere over the Mars Year 36. We present the analysis of the cross-exospheric observations by the EMUS for hydrogen Lyman series and oxygen 130.4 nm emissions and their seasonal variability. The EMUS cross-exospheric observations cover the tangent altitude starting from 130 km to more than 35,000 km above the disk (see Fig. 1), with most of the observations below 25,000 km. The observations show that when Mars moved from perihelion to aphelion, the hydrogen emission line intensities increase by an order of magnitude or more whereas, for oxygen, it is an increment by a factor of about 2 at larger altitudes. Based on these observations, we also discuss the retrieval of densities, temperature, and the estimation of escape fluxes of hydrogen and oxygen species by applying 3D hydrogen ballistic corona and 3D Monte Carlo particle transport models, respectively.Figure 1: The EMM-observed cross-exosphere emission intensity profiles of atomic hydrogen and oxygen during Mars Year 3

One of the primary objectives of the Emirates Mars Mission (EMM) is to study the seasonal variation of the upper atmosphere of Mars and associated changes in the escape of atmosphere to space. Here we present a preliminary analysis of the oxygen population in the inner exosphere (1.06-1.6 Martian radii) with nearly-contiguous sampling across all Martian seasons from early MY 36 to early MY 37. This oxygen is thought to be a non-thermal photochemically generated population driven by solar EUV, which can produce energetic atoms with sufficient velocity to escape Mars’ gravity. The observations are made by measuring the atomic oxygen emission at 130.4 nm using the Emirates Mars Ultraviolet Spectrometer (EMUS). We compare the brightness of the exospheric oxygen population with the thermospheric population ( < 1.06 Mars radii, or < 200 km) and find that the exosphere is much more responsive to seasonal variations in solar energy input. The seasonal variations cannot be explained by modulations in solar irradiance at 130.4 nm alone, and are consistent with the expectation that the extended oxygen exosphere at Mars is generated by a photochemical source.

The surface of the planet Mars exhibits a record of dessiccation and oxidation, the legacy of significant water escape to space as hydrogen and oxygen. This H escape can be constrained using ultraviolet observations of the planet's upper atmosphere, where neutral atomic hydrogen scatters UV sunlight. In the time since its orbit insertion in early 2021, the Emirates Mars Ultraviolet Spectrometer (EMUS) on the Emirates Mars Mission (EMM) has been observing this hydrogen at 102.6 nm and 121.6 nm, H Lyman beta and Lyman alpha. Here we present H escape rates retrieved from these observations, obtained using a 3D radiative transfer model that simulates the brightness of both spectral lines, combining their information content to constrain the atmospheric state. In agreement with past results, we find that H escape peaks around Southern Summer solstice, after perihelion, exhibiting a more than 10x increase relative to Northern Summer conditions. Importantly, our retrievals extract information about both the hydrogen density and temperature, and do not require independent assumptions about the upper atmosphere temperature. We will discuss prospects for extending these retrievals beyond the current EMM dataset as well as implications for the long-term evolution of the Mars atmosphere.

Ions originating from the upper atmosphere of Mars may be picked up by the impinging solar wind and interplanetary magnetic field (IMF), which forms an energetic ion plume from the dayside of the planet as a key feature of the Martian induced magnetosphere and an important ion escape channel. Consisting of mostly ions in the beginning phase of the pickup process, the orientation and morphology of the plume are largely controlled by upstream IMF conditions.Using data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we will perform a thorough investigation of the pickup ion plume under different upstream IMF conditions. Previous statistical ion flux maps by Dong et al. [2015; 2017] from MAVEN data show the plume as a more spatially spread-out feature than that in many simulation models [e.g. Jarvinen et al. 2016 and others], which is possibly due the effects of highly variable IMF conditions for the data used in those maps. We will investigate how the plume appears with selected data under quasi-steady IMF conditions. Furthermore, we will compare the plume under strong and weak IMF conditions, as well as the conditions with IMF approximately perpendicular or parallel to the solar wind direction. The morphology of the plume and characteristics of escaping pickup ions under different IMF conditions will be discussed and compared with available model results to better understand how IMF affects the formation of the plume and ion escape through this channel.

We report the first detailed study of the diurnal thermal structure of upper mesosphere/lower thermosphere (∼80 to 160 km) of Mars from stellar occultation observations by the Imaging Ultraviolet Spectrograph (IUVS) aboard the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. Due to stray light contamination, analyses of this data set to date have been confined to the nighttime events. This study makes use of a revised algorithm for removal of stray light from occultation spectra to retrieve the dayside events as well. The dayside is observed to be warmer than the nightside, with the maximum day/night difference of ∼30 K in the lower thermosphere, ∼20 K around the mesopause, with little diurnal variations at lower altitudes. This is consistent with the radiative time constant which is of the order of 1 Mars day in the urn:x-wiley:21699097:media:jgre22064:jgre22064-math-0001 to urn:x-wiley:21699097:media:jgre22064:jgre22064-math-0002 Pa region. The data also shows that the regions at pressure less than urn:x-wiley:21699097:media:jgre22064:jgre22064-math-0003 Pa are under strong solar control with no prominent migrating tidal signatures. In contrast, on Earth, the radiative time constant near the mesopause is ∼10 Earth days and the temperature variations due to tides are quite large. The Mars Climate Database shows a diurnal trend opposite to the data in the mesosphere, with the dayside mesopause predicted to be cooler than the nightside by ∼10 K along with signatures of a vertically propagating tide. The IUVS data set provides an unprecedented constraint on the structure of the Martian mesosphere. © 2022. American Geophysical Union. All Rights Reserved., The MAVEN mission is supported by NASA through the Mars Exploration Program in association with the University of Colorado and NASA's Goddard Space Flight Center. F.G.-G. is funded by the Spanish Ministerio de Ciencia, Innovación y Universidades, the Agencia Estatal de Investigación 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 Astrofísica de Andalucía (SEV-2017-0709).

Though ion escape to space is an important mechanism for atmospheric loss on Mars, the processes that accelerate ions to escape velocity have not been identifed and quantified. The lowest altitude where suprathermal planetary ions appear is an important source region for ion escape, where electromagnetic forces and waves begin to energize ions to escape velocity. We have conducted a statistical study of O2+ distribution functions measured by Mars Volatile EvolutioN SupraThermal And Thermal Ion Composition (MAVEN-STATIC) in order to identify this source region for Martian ion escape. We have fit Maxwellians to each measured O2+ distribution function in order to identify distributions containing a suprathermal component. Suprathermal ions appear just above the exobase region at all solar zenith angles, but Maxwellian ion distributions persist to higher altitudes near the terminator than on the dayside or the nightside. We also investigated the effects of crustal magnetism, finding that crustal fields protect planetary plasma from energization on the dayside and enhance energization on the nightside.

Fundamentally, what limits the rate of atmospheric ion escape from non-magnetized planets? Previous orbit-based in situ measurements of escaping heavy ions (O+, O2+ and heavier species) at Mars have yielded conflicting estimates of the dependencies on upstream solar wind and solar extreme ultraviolet (EUV) conditions. We compile 7 years (2014-2021) of measured 0.1 eV – 30 keV ion distributions from the STATIC instrument on the MAVEN orbiter to globally map the phase-space ion flux distribution, from which we derive globally integrated outflow, inflow, and net ion fluxes. Through binning the measurements by upstream solar wind (measured simultaneously by the Mars Express orbiter) and EUV conditions, we separately quantify the O+ and O2+ escape dependencies on these external drivers. The found trends indicate that ion escape from Mars is a supply/source-limited process under low solar EUV conditions, however, the appearance and increase of gravitationally bound heavy ion return flows under moderate EUV conditions suggests that the escape process can transition to a Venus-like energy-limited state. The findings show that the state of the ion escape process does not only differ between planets, but the state and thus the drivers of ion escape can also differ under varying external conditions. We discuss the implications for ion observations at Mars during the upcoming solar activity maximum, for the evolution of the Martian atmosphere, and for our understanding of atmospheric ion escape as a general process in the solar system and beyond.

Mars is an unmagnetized planet meaning that it has no internally generated global dipole magnetic field; the solar wind interaction with Mars is thus highly dependent on upstream conditions that include the orientation of the Interplanetary Magnetic Field (IMF). This interaction controls the transfer of energy and momentum from the solar wind into the magnetosphere, ionosphere and atmosphere, driving structure and dynamics within each. The Mars-solar wind interaction has been studied in detail for “nominal” Parker Spiral IMF conditions, but few studies exist that investigate the interaction under less typical “radial IMF” conditions. We utilize in-situ measurements made by NASAs Mars Atmosphere and Volatile EvolutioN (MAVEN) mission during radial IMF conditions at Mars to identify several prominent features that arise during this interaction:Highly disturbed magnetic and plasma conditions exist over the nose of the planet, which are reminiscent of foreshock like conditions and indicative of radial IMF. Solar wind protons and alphas are observed to penetrate directly into the dayside ionosphere down to MAVEN periapsis altitudes (~230 km). The magnetic pileup region (or magnetic barrier) forms deep within the dayside ionosphere, directly exposing significant heavy planetary ion densities above to the solar wind flow. Planetary ions above the magnetic barrier are mass loaded by the solar wind flow, characterized by signatures consistent with VxB acceleration under near radial IMF conditions. Thermal ion distributions in the ionosphere are observed to possess significant suprathermal energetic tails, suggesting that additional energization mechanisms are present that heat the cold ion core. Electron and ion temperatures are 2-10 times higher than average values that occur under more typical IMF conditions. Significant erosion of the dayside upper ionosphere occurs and appears to drive substantial ion escape to space.

Discrete aurorae have been observed at Mars by multiple spacecraft, including Mars Express, Mars Atmosphere and Volatile EvolutioN (MAVEN), and most recently the United Arab Emirates’ Hope spacecraft. Meanwhile, there have been studies on the source particle responsible for producing these detectable aurorae, that is accelerated electrons or hotter solar wind electrons (termed “auroral electrons"). By utilizing empirical criteria to select auroral electrons established by Xu et al. [2022], we conduct statistical analyses of the impact of upstream drivers on the occurrence rate and electron fluxes of auroral electrons. We find the occurrence rate is well organized and increases with upstream dynamic pressure and weakly depends on the interplanetary magnetic field strength. Meanwhile, the integrated auroral electron flux is somewhat insensitive to the upstream drivers. In the meantime, the auroral emission is not the sole effect of electrons impacting the collisional atmosphere. Auroral electrons are expected to cause significant ionization and enhance the plasma density locally. In this study, we also quantify the ionospheric impact of auroral electron precipitation, specifically the thermal ion (O+, O2+, CO2+) density enhancement, with MAVEN observations and also modeling. Our results show the ion density to increase up to 1-2 orders of magnitude at low altitudes.

Water is lost from the Mars upper atmosphere to space as hydrogen and oxygen, both of which can be observed in scattered ultraviolet sunlight at 102.6 nm. We present Emirates Mars Mission Emirates Mars Ultraviolet Spectrometer (EMM/EMUS) insertion orbit observations of this airglow, resolving the independent altitude contributions of H and O for the first time. We present the first airglow modeling of the complete H and O 102.6 nm system and the first 3D azimuthally symmetric modeling of the O emission, retrieving temperatures and densities typical of northern spring. Our model reproduces the emission well above 200 km, but does not incorporate partial frequency redistribution needed to reproduce the observed O brightness at lower altitudes and on the disk. These results support future EMM/EMUS science orbit retrievals of H loss and the use of 102.6 nm observations to constrain planetary atmospheres across the solar system. UAE government; EMM/MBRSC; NASA through the MAVEN mission; KU-CU-LASP Space Sci. [8474000332] Published version Funding for development of the EMM mission was provided by the UAE government, and to co-authors outside of the UAE by MBRSC. Funding for the development of the radiative transfer model was provided by EMM/MBRSC and by NASA through the MAVEN mission. SR and KC are supported by the grant 8474000332-KU-CU-LASP Space Sci.

During the last decade, MAVEN space mission have emphasized a widespread spatial distribution of escaping O+ ions (Brain et al., 2015; Dong et al., 2015; Curry et al., 2015). Statistical studies have demonstrated that such structure is constant and present an asymmetry with respect to the solar wind convective electric field direction. In the Mars Solar Ecliptic coordinate system, continuous large O+ ion fluxes have been observed from the Martian wake to the Northward hemisphere. Global hybrid models have been developed since more than fiffteen years (Modolo et al., 2005, 2016; Brecht and Ledvina, 2006; Kallio et al., 2006) predicting and reproducing successfully the main characteristics of these escaping ion signatures. To further characterize this heavy-ion escape and its variability due to the solar wind forcing, global hybrid simulations have been performed with different set of upstream solar wind parameters. The impact of the solar wind drivers on the dynamics of O+ ion fluxes are reported and compared to the statistical ion fluxes maps derived from MAVEN/STATIC observations (Dong et al., 2015).Brain, D. A., McFadden, J. P., Halekas, J. S., Connerney, J. E. P., Bougher, S. W., Curry, S., et al. (2015). The spatial distribution of planetary ion fluxes near Mars observed by MAVEN. Geophys. Res. Lett. 42, 9142–9148. doi:10.1002/2015GL065293Dong, Y., Fang, X., Brain, D. A., McFadden, J. P., Halekas, J. S., Connerney, J. E., et al. (2015). Strong plume fluxes at Mars observed by MAVEN: An important planetary ion escape channel. Geophys. Res. Lett. 42, 8942–8950. doi:10.1002/2015GL065346Curry, S. M., Luhmann, J. G., Ma, Y. J., Dong, C. F., Brain, D., Leblanc, F., et al. (2015). Response of Mars O+ pickup ions to the 8 March 2015 ICME: Inferences from MAVEN data-based models. Geophys. Res. Lett. 42, 9095–9102. doi:10.1002/2015GL065304Modolo, R., Chanteur, G. M., Dubinin, E., and Matthews, A. P. (2005). Influence of the solar EUV flux on the Martian plasma environment. Annales Geophysicae 23, 433–444. doi:10.5194/angeo-23-433-2005 Brecht, S. H. and Ledvina, S. A. (2006). The Solar Wind Interaction With the Martian Ionosphere/Atmosphere 126, 15–38. doi:10.1007/s11214-006-9084-zKallio, E., Fedorov, A., Budnik, E., Sa¨les, T., Janhunen, P., Schmidt, W., et al. (2006). Ion escape at Mars: Comparison of a 3-D hybrid simulation with Mars Express IMA/ASPERA-3 measurements 182, 350–359. doi:10.1016/j.icarus.2005.09.018

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.

International audience; We report for the first time, simultaneous ion, electron, magnetic field vector and electric field wave measurements made possible by Mars Atmosphere and Volatile EvolutioN, during ion energy flux spikes in low-altitude radial crustal magnetic fields on the Mars dayside. Observations show energetic electrons and ions (E > 25 eV) precipitating on magnetic field lines assumed as closed. Ions (E < 1.4 keV) display broad velocity distributions toward Mars, showing ions flowing from higher altitude possibly after magnetic reconnection or loss cone filling from pitch angle scattering effects. Precipitating ions (E < 1.4 keV) show nonadiabatic features depending on ion mass and energy and returning ions (E < 1.4 keV) show evidence of conserving the first adiabatic invariant in a mirror field. We observe magnetic field perturbations up to 60 nT, electric field wave amplitudes up to 38 mV/m, and brief periods of peaked electron spectra. At ∼175 km and at times Mars Atmosphere and Volatile EvolutioN is below the mirroring altitude of electrons, we observe mirroring and transverse heating of H+ ions alongside increased electric field wave amplitude fluctuations. It suggests field aligned potential drops result from different mirror altitudes of ions and electrons. Ions E > 1.4 keV (O+) occur as injected accelerated ion beams and ions heated after energization or deceleration. Energy dispersed kilo-electron-volt ions suggest a selection effect in radial magnetic fields for lower-energy Marsward ions, compared to reflection of higher-energy anti-Sunward ions. Precipitating kilo-electron-volt ions show energy deposition rates of 3.6 ×10-6 W/m2 and sputtering escape rates from precipitating O+ ions of 1.5 ×105/(cm2.s) and 2.1 ×106/(cm2.s) are calculated.

International audience; In this work, we study the influence of the September 2017 solar event on the precipitating heavy ion fluxes towards Mars' atmosphere as seen by MAVEN/SWIA, an energy and angular ion spectrometer and by MAVEN/STATIC, an energy, mass and angular ion spectrometer. After a careful reconstruction of the background induced by the Solar Energetic Particle (SEP) event in the MAVEN/SWIA spectrometer, we investigate the precipitating ion flux responses to the space weather events that took place in September 2017. This period is a unique opportunity to analyze the respective role of various possible drivers of heavy ion precipitation into Mars’ atmosphere with a wide range of different space weather events occurring during the same month. This study shows an increase in the precipitation flux by more than one order of magnitude during the arrival of the September Interplanetary Coronal Mass Ejection (ICME) compared to the average flux during quiet solar conditions. We also showed that among the possible solar drivers, the solar wind dynamic pressure is the most significant during September 2017.

The Parker Solar Probe (PSP) spacecraft completed its second Venus gravity assist maneuver (VGA2) on 2019 December 26. For a 20 minute interval surrounding closest approach, the PSP/FIELDS Radio Fr...

We outline specific steps that NASA and the space science community can take to advance collaboration and coordination between the communities represented by the four NASA Science Mission Directorate Divisions. It is important to note that the only way that this effort can succeed is if NASA initiates and supports it through directed resources.

International audience; Depressions in magnetic field strength, commonly referred to as magnetic holes, are observed ubiquitously in space plasmas. Subproton-scale magnetic holes with spatial scales smaller than or on the order of a proton gyroradius, are likely supported by electron current vortices, rotating perpendicular to the ambient magnetic field. While there are numerous accounts of subproton-scale magnetic holes within the Earth’s magnetosphere, there are few, if any, reported observations in other space plasma environments. We present the first evidence of subproton-scale magnetic holes in the Venusian magnetosheath. During Parker Solar Probe’s first Venus Gravity Assist, the spacecraft crossed the planet’s bow shock and subsequently observed the Venusian magnetosheath. The FIELDS instrument suite onboard the spacecraft achieved magnetic and electric field measurements of magnetic hole structures. The electric fields associated with magnetic depressions are consistent with electron current vortices with amplitudes on the order of 1µA/m2.

Multi-spacecraft missions after 2000 (Cluster II, THEMIS, Van Allen Probes, and MMS) have revolutionized our understanding of the causes, patterns and variability of a wide array of plasma phenomena in the terrestrial magnetospheric environment. ESCAPADE is a twin-spacecraft Mars mission concept that will similarly revolutionize our understanding of how solar wind momentum and energy flows throughout Mars’ magnetosphere to drive ion and sputtering escape, two processes which have helped shape Mars’ climate evolution over solar system history. ESCAPADE will measure magnetic field strength and topology, ion plasma distributions (separated into light and heavy masses), as well as suprathermal electron flows and thermal electron and ion densities, from coordinated elliptical, 200 km x ~7000 km orbits. ESCAPADE are small spacecraft ( ESCAPADE is due to complete its preliminary design review in August 2020, thereafter moving toward build, test, integration and launch two years later. We will report on science goals and objectives, mission design challenges, and provide a status update.

The recent discoveries of telluric exoplanets in the habitable zone of different stars have led to questioning the nature of their atmosphere, which is required to determine their habitability. Atmospheric escape is one of the challenging problems to be solved: simply adapting what is currently observed in the solar system is doomed to fail due to the large variations in the conditions encountered around other stars. A better strategy is to review the different processes that shaped planetary atmospheres and to evaluate their importance depending upon the stellar conditions. This approach allowed us to show that processes like ion-pickup were a more important way to lose atmosphere at Mars in the past. We reviewed the different escape mechanisms and their magnitude in function of the different conditions. This led us to discover discrepancies in the current literature concerning problems such as the Xenon paradox or the importance of a magnetic field in protecting an atmosphere.This shows that one should be very careful before claiming the presence of an atmosphere on planets in the habitable zone of their M-dwarfs: new criteria such as the Alfven surface location with respect to the planet should be taken into account a-priori.Overall, the habitability of a planet should not be claimed only on by its location in the habitable zone but also after careful analysis of the interaction between its atmosphere and its parent star [Gronoff et al. 2020]. Gronoff, G., Arras, P., Baraka, S., Bell, J. M., Cessateur, G., Cohen, O., et al. ( 2020). Atmospheric Escape Processes and Planetary Atmospheric Evolution. Journal of Geophysical Research: Space Physics, 125, e2019JA027639. https://doi.org/10.1029/2019JA027639

Superthermal electron precipitation is one of the main sources supporting the Mars nightside ionosphere. It is expected that solar wind electron fluxes are to increase significantly during interplanetary coronal mass ejections (ICME) and therefore an enhanced nightside ionospheric density. This study is to quantify the variation of the precipitating and deposited electron fluxes during five of the most extreme ICMEs encountered by Mars Global Surveyor (MGS). We find energy fluxes correlate better with the upstream dynamic pressure proxy than number fluxes and electron fluxes increase more at high energies, which means electrons tend to have a lower peak production altitude during storm times. The precipitating and net/deposited fluxes are increased up to an order of magnitude from low to high dynamic pressures. The estimated total electron content (TEC) is a few times of 1014 m-2 for quiet times and on the order of 1015 m-2 for storm times, with an enhancement up to an order of magnitude locally near strong crustal fields. Crustal magnetic fields have an effect on the deposited fluxes with more prominent magnetic reflection over strong magnetic fields during quiet periods, which is significantly reduced during storm times. Lastly, we estimate a global energy input from downward fluxes of 1.3×108 W and 5.5×108 W and the globally deposited energy from net fluxes of 2.3×107 W and 1.6×108 W for quiet and storm time periods, a factor of 4 and 7 enhancement globally, respectively, but up to an order of magnitude locally near strong crustal fields.

We advocate for a mission concept study for a space telescope dedicated to solar system science in Earth orbit. Such a study was recommended by the Committee on Astrobiology and Planetary Science (CAPS) report "Getting Ready for the Next Planetary Science Decadal Survey." The Mid-Decadal Review also recommended NASA to assess the role and value of space telescopes for planetary science. The need for high-resolution, UV-Visible capabilities is especially acute for planetary science with the impending end of the Hubble Space Telescope (HST); however, NASA has not funded a planetary telescope concept study, and the need to assess its value remains. Here, we present potential design options that should be explored to inform the decadal survey., Whitepaper submitted to Planetary Science and Astrobiology Decadal Survey

The habitability of the surface of any planet is determined by a complex evolution of its interior, surface, and atmosphere. The electromagnetic and particle radiation of stars drive thermal, chemical and physical alteration of planetary atmospheres, including escape. Many known extrasolar planets experience vastly different stellar environments than those in our Solar system: it is crucial to understand the broad range of processes that lead to atmospheric escape and evolution under a wide range of conditions if we are to assess the habitability of worlds around other stars. One problem encountered between the planetary and the astrophysics communities is a lack of common language for describing escape processes. Each community has customary approximations that may be questioned by the other, such as the hypothesis of H-dominated thermosphere for astrophysicists, or the Sun-like nature of the stars for planetary scientists. Since exoplanets are becoming one of the main targets for the detection of life, a common set of definitions and hypotheses are required. We review the different escape mechanisms proposed for the evolution of planetary and exoplanetary atmospheres. We propose a common definition for the different escape mechanisms, and we show the important parameters to take into account when evaluating the escape at a planet in time. We show that the paradigm of the magnetic field as an atmospheric shield should be changed and that recent work on the history of Xenon in Earth's atmosphere gives an elegant explanation to its enrichment in heavier isotopes: the so-called Xenon paradox.

Multi-spacecraft missions after 2000 (Cluster II, THEMIS, Van Allen Probes, and MMS) have revolutionized our understanding of the causes, patterns and variability of a wide array of plasma phenomena in the terrestrial magnetospheric environment. ESCAPADE is a twin-spacecraft Mars mission concept that will similarly revolutionize our understanding of how solar wind momentum and energy flows throughout Mars’ magnetosphere to drive ion and sputtering escape, two processes which have helped shape Mars’ climate evolution over solar system history. ESCAPADE will measure magnetic field strength and topology, ion plasma distributions (separated into light and heavy masses), as well as suprathermal electron flows and thermal electron and ion densities, from elliptical, 200 km x 7000 km orbits. ESCAPADE are small spacecraft (ESCAPADE has been selected for Phase A and B study by NASA as one of three finalists in the SIMPLEX-II program. We will report on science goals, engineering and mission design challenges, and provide a status update.

The solar wind is slowed, deflected, and heated as it encounters Venus's induced magnetosphere. The importance of kinetic plasma processes to these interactions has not been examined in detail, due to a lack of constraining observations. In this study, kinetic‐scale electric field structures are identified in the Venusian magnetosheath, including plasma double layers. The double layers may be driven by currents or mixing of inhomogeneous plasmas near the edge of the magnetosheath. Estimated double‐layer spatial scales are consistent with those reported at Earth. Estimated potential drops are similar to electron temperature gradients across the bow shock. Many double layers are found in few high cadence data captures, suggesting that their amplitudes are high relative to other magnetosheath plasma waves. These are the first direct observations of plasma double layers beyond near‐Earth space, supporting the idea that kinetic plasma processes are active in many space plasma environments., Key Points Plasma double layers are detected near the Venusian bow shockMultiple double layers are identified in a small amount of burst dataKinetic processes may help mediate interaction between the solar wind and induced magnetospheres

The National Academy Committee on Astrobiology and Planetary Science (CAPS) made a recommendation to study a large/medium-class dedicated space telescope for planetary science, going beyond the Discovery-class dedicated planetary space telescope endorsed in Visions and Voyages. Such a telescope would observe targets across the entire solar system, engaging a broad spectrum of the science community. It would ensure that the high-resolution, high-sensitivity observations of the solar system in visible and UV wavelengths revolutionized by the Hubble Space Telescope (HST) could be extended. A dedicated telescope for solar system science would: (a) transform our understanding of time-dependent phenomena in our solar system that cannot be studied currently under programs to observe and visit new targets and (b) enable a comprehensive survey and spectral characterization of minor bodies across the solar system, which requires a large time allocation not supported by existing facilities. The time-domain phenomena to be explored are critically reliant on high spatial resolution UV-visible observations. This paper presents science themes and key questions that require a long-lasting space telescope dedicated to planetary science that can capture high-quality, consistent data at the required cadences that are free from effects of the terrestrial atmosphere and differences across observing facilities. Such a telescope would have excellent synergy with astrophysical facilities by placing planetary discoveries made by astrophysics assets in temporal context, as well as triggering detailed follow-up observations using larger telescopes. The telescope would support future missions to the Ice Giants, Ocean Worlds, and minor bodies across the solar system by placing the results of such targeted missions in the context of longer records of temporal activities and larger sample populations., Comment: A whitepaper submitted to the Planetary Science Decadal Survey

International audience; We discuss the influence of the solar wind dynamic pressure on the ion precipitation using observations performed by MAVEN from the 04 June 2014 to the 20 July 2017. The increase of the dynamic pressure from 0.63 to 1.44nPa is clearly associated with an increase of the same order of magnitude of the precipitating oxygen ion energy flux measured by MAVEN/STATIC from 9.9 to 20.6 × 106eV. cm−2. sr−1. s−1at low energy (from 30 to 650 eV). In the same way, from 650 eV to 25000 eV, MAVEN/SWIA (all species) observed an increase from 22.4 to 42.8 × 107eV. cm−2. sr−1. s−1 of the precipitating ion energy flux.Performing two simulations using the average solar wind conditions for both solar dynamic pressure regimes observed by MAVEN as input of the LatHyS model (LATMOS Hybrid Simulation), we reproduce some of the key characteristics of the observed oxygen ion precipitation. We characterize the oxygen ions simulated by LatHyS by their energy and time of impact, their time of injection in the simulation and initial position and the mechanism by which these ions were created. The model suggests that the main cause of the increase of the heavy ion precipitation during an increase of the solar dynamic pressure is the increase of the ion production by charge exchange, proportional to the increase of the solar wind flux, which becomes the main contribution to the ion precipitation at high energy.

International audience; Many aspects of the Sun-Mars interaction have been investigated during solar transient events with measurements from multiple spacecrafts and also simulation efforts. Limited discussion has been paid to magnetic topology response to disturbed upstream conditions. The implications of topology changes include, but are not limited to, the pattern of energetic particle precipitation into the Martian atmosphere and the impact on cold ion escape during solar transient events as low-energy ion escape is dependent on magnetic topology. In this study, we investigate the magnetic topology response to the 2017 September interplanetary coronal mass ejection (ICME) event with measurements collected by the Mars Atmospheric and Volatile EvolutioN spacecraft. It is found that the interface between draped interplanetary magnetic field and closed field lines was moved from 800-1400 km in altitude during quiet conditions to 200-400 km after ICME arrived at Mars and then relaxed back to high altitudes again after the event. To gain insight into magnetic topology response on a global scale, we first validate magnetic topology from a time-dependent simulation with a single-fluid multispecies magnetohydrodynamic (MHD) model by comparing magnetic topology determined from Mars Atmospheric and Volatile EvolutioN data, which shows a good agreement. Then we present MHD predictions of global magnetic topology changes during this ICME event. In addition to a deeper interplanetary magnetic field penetration, MHD results suggest more open field lines in response to the ICME event.