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International audience; 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 particles responsible for producing these detectable aurorae (termed "auroral electrons"). By utilizing empirical criteria to select auroral electrons established by Xu et al. (2022, https://doi.org/10.1029/2022GL097757), we conduct statistical analyses of the impact of upstream drivers on the occurrence rate and fluxes of auroral electrons. We find the occurrence rate increases with upstream dynamic pressure and weakly depends on the interplanetary magnetic field strength. Meanwhile, the integrated auroral electron flux somewhat decreases with increasing upstream drivers. Auroral electron precipitation also occurs more frequently and is more intense over regions of strong crustal fields compared to weak crustal fields. Aside from emissions, auroral electrons are expected to cause significant impact ionization and enhance the plasma density locally. In this study, we also quantify the nightside ionospheric impact of auroral electron precipitation, specifically the thermal ion (O+, O2+, and CO2+) density enhancement, with MAVEN observations. Our results show that the ion density is increased by up to an order of magnitude at low altitudes. The crustal effects on ion density profiles for nominal electron and auroral electron precipitation are also discussed.

International audience; The Martian bow shock is a rich example of a supercritical, mass-loaded collisionless shock that coexists with ultra-low frequency upstream waves that are generated by the pick-up of exospheric ions. The small size of the bow shock stand-off distance (comparable with the solar wind ion convective gyroradius) raises questions about the nature of the particle acceleration and energy dissipation mechanism at work. The study of the Martian shock structure is crucial to understand its microphysics and is of special interest to understand the solar wind—planet interaction with a virtually unmagnetized body. We report on a complete identification and first characterization of the supercritical substructures of the Martian quasi-perpendicular shock, under the assumption of a moving shock layer, using MAVEN magnetic field and solar wind plasma observations for two examples of shock crossings. We obtained substructures length-scales comparable to those of the Terrestrial shock, with a narrow shock ramp of the order of a few electron inertial lengths. We also observed a well defined foot (smaller than the proton convected gyroradius) and overshoot that confirm the importance of ion dynamics for dissipative effects.

In situ measurements of ionospheric and thermospheric temperatures are experimentally challenging because orbiting spacecraft typically travel supersonically with respect to the cold gas and plasma. We present

International audience; The ionospheric electron temperature is important for determining the neutral/photochemical escape rate from the Martian atmosphere via the dissociative recombination of O2+. The Langmuir Probe and Waves instrument onboard MAVEN (Mars Atmosphere and Volatile EvolutioN) measures electron temperatures in the ionosphere. The current paper studies electron temperatures in the dayside for two regions where (1) crustal magnetic fields are dominant and (2) draped magnetic fields are dominant. Overall, the electron temperature is lower in the crustal-field regions, namely, the strong magnetic field region, which is due to a transport of cold electrons along magnetic field lines from the lower to upper atmosphere. The electron temperature is also greater for high solar extreme ultraviolet conditions, which is associated with the local extreme ultraviolet energy deposition. The current models underestimate the electron temperature above 250-km altitude in the crustal-field region. Electron heat conduction associated with a photoelectron transport in the crustal-field regions is altered due to kinetic effects, such the magnetic mirror and/or ambipolar electric field because the electron mean free path exceeds the relevant length scale for electron temperature. The mirror force can affect the electron and heat transport between low altitudes, where the neutral density and related electron cooling rates are the greatest, and high altitudes, while the ambipolar electric field decelerates the electron's upward motion. These effects have not been included in current models of the electron energetics, and consideration of such effects on the electron temperature in the crustal-field region should be considered for future numerical simulations.

We model expected dynamo currents above, and resulting magnetic field profiles at, InSight's landing site on Mars, including for the first time the effect of electron-ion collisions. We calculate their diurnal and seasonal variability using inputs from global models of the Martian thermosphere, ionosphere, and magnetosphere. Modeled currents primarily depend on plasma densities and the strength of the neutral wind component perpendicular to the combined crustal and draped magnetic fields that thread the ionosphere. Negligible at night, currents are the strongest in the late morning and near solstices due to stronger winds and near perihelion due to both stronger winds and higher plasma densities from solar EUV photoionization. Resulting surface magnetic fields of tens of nanotesla and occasionally >100 nT may be expected at the InSight landing site. We expect currents and surface fields to vary significantly with changes in the draped magnetic field caused by Mars' dynamic solar wind environment. ©2019. American Geophysical Union. All Rights Reserved., R. J. L., C. M. F., and L. A. were funded by the NASA MAVEN mission prime contract. M. O. F. was funded by the NASA Insight mission prime contract. F. G. G. was funded by the Spanish National Research Council (CSIC) under intramural project CSIC 201450E022 and acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia-CSIC (SEV-2017-0709). F. F. was funded by the French Centre National De La Recherche Scientifique.

International audience; Open and draped magnetic field topologies are important at Mars because they can provide ionospheric particles a path to escape to space. Four years of Mars Atmosphere and Volatile EvolutioN data are analyzed in this study, demonstrating that the altitude at which the ionospheric density drops below 102 cm-3 is essentially coincident with the altitude down to which open and draped magnetic field lines are observed in the ionosphere. During times of enhanced solar wind dynamic pressure, a greater fraction of the magnetic topology was observed as open or draped (as opposed to closed) above densities of 102 cm-3. The altitudes at which the ionospheric density fell below 102 cm-3, and the magnetic field topology transitioned from closed to open or draped, also decreased during higher dynamic pressure conditions. Times of enhanced solar wind dynamic pressure thus appear to drive greater penetration of draped magnetic field into the ionosphere, enhancing the rate of reconnection between draped and crustal magnetic fields and producing more open field. Such observations may have implications for the long-term evolution of the Martian ionosphere; the historic solar wind is thought to have been denser and faster than present-day conditions, and "quiet time" conditions may have been equivalent to extreme dynamic pressure events today. Depending on past atmospheric conditions at Mars, draped topology may have routinely penetrated deep into the ionosphere, and quiet time rates of ionospheric escape to space may thus have been much greater for early Mars than today.

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.

We use more than 10years of the Martian topside ionospheric data measured by the Mars Advanced Radar for Subsurface and Ionosphere Sounding radar sounder on board the Mars Express spacecraft to der ...

The objective of this White Paper, submitted to ESA’s Voyage 2050 call, is to get a more holistic knowledge of the dynamics of the Martian plasma system, from its surface up to the undisturbed solar wind outside of the induced magnetosphere. This can only be achieved with coordinated multi-point observations with high temporal resolution as they have the scientific potential to track the whole dynamics of the system (from small to large scales), and they constitute the next generation of the exploration of Mars analogous to what happened at Earth a few decades ago. This White Paper discusses the key science questions that are still open at Mars and how they could be addressed with coordinated multipoint missions. The main science questions are: (i) How does solar wind driving impact the dynamics of the magnetosphere and ionosphere? (ii) What is the structure and nature of the tail of Mars’ magnetosphere at all scales? (iii) How does the lower atmosphere couple to the upper atmosphere? (iv) Why should we have a permanent in-situ Space Weather monitor at Mars? Each science question is devoted to a specific plasma region, and includes several specific scientific objectives to study in the coming decades. In addition, two mission concepts are also proposed based on coordinated multi-point science from a constellation of orbiting and ground-based platforms, which focus on understanding and solving the current science gaps. Part of a collection: Voyage 2050 – science themes for ESA’s long-term plan for the science programme: Solar Systems, ours and others (Part 2).

Thermal (, 10 pages, 7 figures

Tobacco smoke exposure is a major risk factor for the health of children and adolescents with CF. In this study, we assess whether cessation of smoke exposure is associated with improved outcomes in this population.We used annualized and encounter-based data from the U.S. CF Foundation Patient Registry (2006-2018) on all individuals born 1998-2010. The analytical sample included those who ever reported second-hand smoke exposure (daily or weekly), ever lived with a smoker, or ever reported smoking themselves. We used non-linear mixed models for pulmonary exacerbations and linear mixed models for ppFEVThe sample included 3,633 individuals contributing 19,629 person-years. Cessation of smoke exposure reduced the odds of a pulmonary exacerbation in 12 months by 17% (OR 0.83, p 0.001) in the first year of cessation, with an additional 6% decrease (OR 0.94, p = 0.003) for each additional year of cessation. Cessation was associated with improvements in ppFEVEliminating smoke exposure may reduce pulmonary exacerbations and improve respiratory and nutritional outcomes in children and adolescents with CF. Both smoking cessation and exposure prevention should be prioritized in pediatric CF care.

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 ionopause is a tangential discontinuity in the ionospheric thermal plasma density profile that marks the upper boundary of the ionosphere for unmagnetized planets. Since only Venus and Mars have no global “dipole” magnetic fields, ionopauses are unique to those planets. For Venus, the ionopause formation is well characterized because the thermal pressure of the ionosphere is usually larger than the solar wind dynamic pressure. For Mars, however, the maximum thermal pressure of the ionosphere is usually insufficient to balance the total pressure in the overlying magnetic pileup boundary. Therefore, the Martian ionopause is not always formed, and when it does, it is highly structured and is located at different altitudes. In this study, we characterise the Martian ionopause formation from the point of view of the electron density and electron temperature, as well as the thermal, magnetic and dynamic pressures. The objective is to investigate under which circumstances the Martian ionopause is formed, both over and far from crustal magnetic fields, and compare to the Venus’ case. We use several multi-plasma and magnetic field in-situ observations from the three deep dip campaigns of the MAVEN mission that occurred on the dayside of Mars (near subsolar point), as well as in-situ solar wind plasma observations from the Mars Express mission. We find that that 36% of the electron density profiles over strong crustal magnetic field regions had an ionopause event in contrast to the 54% of electron density profiles far from strong crustal magnetic field regions. We also find that the topside ionosphere is typically magnetized at mostly all altitudes. The ionopause, if formed, occurs where the total ionospheric pressure (magnetic+thermal) equals the upstream solar wind dynamic pressure.

Background The ion temperature is a key parameter controlling the structure of planetary ionospheres. In the lower ionosphere, where ion motion is dominated by collisions with neutrals, ion temperatures directly affect collision frequencies. At higher altitudes, in the collisionless regime, ion temperatures influence whether some fraction of the distribution can overcome the planet’s gravity to escape to space. Reliable knowledge of ion temperatures is critical to understanding current ionospheric structures as well as the long-term evolution of planetary atmospheres. For nearly 40 years, the only in-situ measurements of ion temperatures at Mars were obtained from ~375 km to ~120 km altitude during the descents of the Viking landers in 1976 [1]. These measurements were made by retarding potential analyzers. Assumptions about ion composition were required to derive temperatures, and all ion species were assumed to be the same temperature. While this assumption is reasonable in the collisional regime below the exobase (~200 km), mass-dependent electromagnetic acceleration can cause temperatures to diverge at higher altitudes. Until recently, ion temperatures at Mars have primarily been investigated using models. The majority of work has focused on explaining elevated electron temperatures in the upper ionosphere, concluding that a topside heat source (e.g. the solar wind) is required to achieve agreement between modeled profiles and Viking observations [2, 3]. The Combined Atmospheric Photochemistry and Ion Tracing (CAPIT) model reproduced Viking profiles by tracing ion paths while accounting for magnetic fields, major chemical reactions, and wave heating [4]. Models of the solar wind interaction with Mars (e.g. [5],[6]) have traditionally adopted a simplified lower boundary assuming equal electron and ion temperatures, which is significantly in error above ~200 km, in contrast to findings by Matta et al. [7] that different ion species have different temperatures. Recently, Ma et al. [8] showed that the electron pressure gradient significantly affects ion temperatures. Since 2014, comprehensive measurements of the ionosphere above 120 km have been made by the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter at all local times and most latitudes. Studies based on these data are beginning to revolutionize our understanding of the planet’s ionosphere. In this study, we use data collected by the MAVEN SupraThermal And Thermal Ion Composition (STATIC) instrument to present the first measurements of ion temperature at Mars since the Viking landers. Methodology We will present O2+ temperature profiles measured in the Martian ionosphere by STATIC. STATIC measures ion energies from 0.1 eV to 30 keV over a 360°x90° field of view, with mass resolution capable of distinguishing the main ionospheric and escaping species: CO2+, O2+, O+, and H+ [9]. Several instrumental effects contribute to the challenge of extracting ion temperatures from STATIC data, some of which require empirical corrections that are currently being calculated. Three different methods are used to calculate the O2+ temperature using different assumptions which are valid over different, overlapping altitude ranges. These calculations include corrections for spacecraft potential, ion suppression, and instrument response, as well as backscatter, straggling, and molecular fragmentation inside the instrument, among other effects. These calibrations have not been finalized, meaning that the O2+ temperatures presented require further correction. Selection of the best temperature is based on characteristics of the measured distribution. If the population is beam-like (i.e. narrow in energy or angle), then the width of the beam indicates the temperature. However, if the distribution is broad, then calculating moments of the three-dimensional velocity distribution function provides a kinetic temperature, which can be higher than the thermal temperature of the Maxwellian core of the distribution. Once temperatures have been calculated, the data are processed automatically to determine which estimate is the most appropriate. The resulting temperature profiles are largely continuous from MAVEN’s periapsis near 150 km up to altitudes well above 350 km. Results and Discussion We present O2+ temperature profiles measured by STATIC when MAVEN’s periapsis occurred close to local noon, midnight, dawn, and dusk. These temperature profiles will be presented alongside the neutral Ar temperature measured by the Neutral Gas and Ion Mass Spectrometer, and the electron temperature measured by the Langmuir Probe and Waves experiment [10, 11]. We use profiles measured on the inbound segment of the orbit to minimize the effect of changing solar zenith angle. In addition, Ar temperatures are only available on the inbound segment. The Ar temperature is expected to be representative of the entire neutral population. At altitudes below ~250 km, the ion distribution is usually dominated by O2+, and we anticipate that all ions will converge to the O2+ temperature. The ion, neutral, and electron temperatures are expected to converge below the exobase, where high collision rates force these populations to equilibrate. Although this thermalization begins to occur below ~200 km, temperature differences between Ar and O2+ persist down to MAVEN’s periapsis of 150 km. The electron temperature is several times higher than the ion temperature in this altitude range, contrary to the assumptions made in most modeling studies. We note differences in profiles measured at different local times. Unsurprisingly, the median periapsis ion temperature at midnight is colder than at noon, reaching ~250 K at noon compared to ~175 K at midnight. Variations in temperature between successive orbits are larger on the nightside than the dayside, indicated by the larger range of temperatures measured on the nightside, which is to be expected due to the patchy, tenuous nature of the nightside ionosphere. Measuring the cold thermal ion temperature at another planet poses many challenges. MAVEN STATIC is the first instrument capable of making such measurements at Mars–indeed, it is the first instrument capable of measuring the ion temperature since the Viking landers. Substantial progress has been made toward deriving ion temperatures from STATIC. Once the necessary calibrations are finalized, O2+ temperatures will be calculated for nearly the entire MAVEN mission, providing a new tool for systematically analyzing the Martian atmosphere. References [1] Hanson et al. https://doi.org/10.1029/JS082i028p04351 [2] Shinagawa & Cravens. https://doi.org/10.1029/JA094iA06p06506 [3] Cui et al. https://doi.org/10.1002/2014JE004726 [4] Andersson et al. https://doi.org/10.1016/j.icarus.2009.07.009 [5] Dong et al. https://doi.org/10.1002/2014GL059515 [6] Brecht & Ledvina. https://doi.org/10.1016/j.icarus.2009.04.028 [7] Matta et al. https://doi.org/10.1016/j.icarus.2013.09.006 [8] Ma et al. https://doi.org/10.1029/2019JA027091 [9] McFadden et al. https://doi.org/10.1007/s11214-015-0175-6 [10] Stone et al. https://doi.org/10.1029/2018JE005559 [11] Ergun et al. https://doi.org/10.1002/2015GL065280

The thermal electron temperature is an important parameter for planetary ionospheres because it drives several important processes in the photochemical region of the atmosphere. Various electron-neutral collision and ion dissociative recombination rates depend on the thermal electron temperature, which thus strongly influences the structure and composition of the ionosphere. The production of hot neutral atoms via the dissociative recombination of molecular ions (in particular O2+ to hot O) can drive atmospheric escape to space, and the thermal electron temperature is thus also important for the long term evolution of the Martian atmosphere. Multiple studies have attempted to model the thermal electron temperature profile at Mars but have been unable to match observations. A topside heat flux from the solar wind interaction with Mars is typically invoked in these models to bring modeled temperatures into agreement with observations [1, 2, 3, 4]. The similar scale size of the Martian magnetosphere with respect to the proton gyro radius in the upstream solar wind has long been posited as a facilitator for efficient wave-particle interactions between waves generated at the Martian bow shock, and charged particles in the topside ionosphere, to provide this topside heat flux [5, 6]. However, detailed observations of the relevant plasma characteristics required to investigate such wave-particle interactions in detail have been lacking at Mars, until the arrival of the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission in the fall of 2014. We present here MAVEN observations of such wave-particle interactions, driven by periodic (~ 25 s) large scale (100s km) magnetosonic waves propagating from the shock/sheath region into the Martian dayside upper ionosphere. These waves adiabatically modulate the suprathermal electron distribution function, and the induced electron temperature anisotropies drive the generation of observed electromagnetic whistler waves. The localized (in altitude) minimum in the ratio fpe / fce provides conditions favorable for the local enhancement of efficient wave-particle interactions, so that the induced whistlers act back on the suprathermal electron population to isotropize the plasma through pitch angle scattering. These wave-particle interactions break the adiabaticity of the large scale magnetosonic wave compressions, leading to local heating of the suprathermal electrons during compressive wave `troughs'. Further evidence of this heating is observed as the subsequent phase shift between the observed perpendicular-to-parallel suprathermal electron temperatures and compressive wave fronts. Full details are presented in [7]. Because the primary heat source for thermal electrons in the Martian ionosphere is heating via collisions with suprathermal electrons [8, 9], the above heating mechanism may thus play an important role in driving the enhanced thermal electron temperatures that have long been reported in the upper ionosphere of Mars. Such a heating mechanism may also be important at other unmagnetized bodies such as Venus and comets. [1] Hanson, W. B., & Mantas, G. P. (1988). Viking electron temperature measurements: Evidence for a magnetic field in the Martian ionosphere. Journal of Geophysical Research: Space Physics, 93(A7), 7538-7544. [2] Chen, R. H., Cravens, T. E., & Nagy, A. F. (1978). The Martian ionosphere in light of the Viking observations. Journal of Geophysical Research: Space Physics, 83(A8), 3871-3876. [3] Choi, Y. W., Kim, J., Min, K., Nagy, A. F., & Oyama, K. I. (1998). Effect of the magnetic field on the energetics of Mars ionosphere. Geophysical research letters, 25(14), 2753-2756. [4] Cui, J., Galand, M., Zhang, S. J., Vigren, E., & Zou, H. (2015). The electron thermal structure in the dayside Martian ionosphere implied by the MGS radio occultation data. Journal of Geophysical Research: Planets, 120(2), 278-286. [5] Moses, S. L., Coroniti, F. V., & Scarf, F. L. (1988). Expectations for the microphysics of the Mars‐solar wind interaction. Geophysical Research Letters, 15(5), 429-432. [6] Ergun, R. E., Andersson, L., Peterson, W. K., Brain, D., Delory, G. T., Mitchell, D. L., ... & Yau, A. W. (2006). Role of plasma waves in Mars' atmospheric loss. Geophysical research letters, 33(14). [7] Fowler, C. M., Agapitov, O. V., Xu, S., Mitchell, D. L., Andersson, L., Artemyev, A., ... & Mazelle, C. (2020). Localized Heating of the Martian Topside Ionosphere Through the Combined Effects of Magnetic Pumping by Large‐Scale Magnetosonic Waves and Pitch Angle Diffusion by Whistler Waves. Geophysical Research Letters, 47(5), e2019GL086408. [8] Fox, J. L., & Dalgarno, A. (1981). Ionization, luminosity, and heating of the upper atmosphere of Venus. Journal of Geophysical Research: Space Physics, 86(A2), 629-639. [9] Torr, M. R., Richards, P. G., & Torr, D. G. (1980). A new determination of the ultraviolet heating efficiency of the thermosphere. Journal of Geophysical Research: Space Physics, 85(A12), 6819-6826.

This is an excel data file for an analysis of NASA MAVEN date looking at magnetic reconnection in the ionosphere. It will accompany a later paper in the J. Geophysical Research on this topic.

This study assesses under what circumstances the Martian ionopause is formed on the dayside, both in regions where there are strong crustal magnetic fields and areas where these fields are small (

The Magnetic Pileup Boundary or Induced Magnetosphere Boundary (IMB) has been an enigma in Mars aeronomy. Previously dubbed the planetopause, magnetopause, ion-composition boundary, and protonopaus...

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.

International audience; We present Mars Atmosphere and Volatile EvolutioN (MAVEN) observations of periodic (∼25 s) large-scale (hundreds of km) magnetosonic waves propagating into the Martian dayside upper ionosphere. These waves adiabatically modulate the superthermal electron distribution function, and the induced electron temperature anisotropies drive the generation of observed electromagnetic whistler waves. The localized (in altitude) minimum in the ratio fpe/fce provides conditions favorable for the local enhancement of efficient wave-particle interactions, so that the induced whistlers act back on the superthermal electron population to isotropize the plasma through pitch angle scattering. These wave-particle interactions break the adiabaticity of the large-scale magnetosonic wave compressions, leading to local heating of the superthermal electrons during compressive wave "troughs." Further evidence of this heating is observed as the subsequent phase shift between the observed perpendicular-to-parallel superthermal electron temperatures and compressive wave fronts. This heating mechanism may be important at other unmagnetized bodies.

Martian sub-solar electron temperatures obtained below 250 km are examined using data obtained by instruments on the Mars Atmosphere Evolution Mission (MAVEN) during the three sub-solar deep dip ca...

International audience; From February to March 2019, the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft repeatedly observed aurora near periapsis over Mars' southern strong crustal fields. During these orbits, the Solar Wind Electron Analyzer observed accelerated electrons at similar locations to where the auroras were observed, resembling the inverted-V structure observed near Earth's auroral region. In this study, we present a case study of such an acceleration event, where we estimate a field-aligned electrostatic potential drop of ∼440 V. We determine the field-aligned current from the observed magnetic perturbation reaches 1.1 μA/m2, agreeing reasonably well with the estimated net electron current carried by acceleration electrons with a maximum of 2.5 μA/m2. Similar to Earth, the potential drop develops when the ambient plasma cannot sustain the imposed field-aligned current. We also estimate the potential layer to be located above 750- to 850-km altitude and the associated electric field to be ∼0.6 V/m.

International audience; Using data from the National Aeronautics and Space Administration Mars Atmosphere and Voltatile EvolutioN and the European Space Agency Mars Express spacecraft, we show that transient phenomena in the foreshock and solar wind can directly inject energy into the ionosphere of Mars. We demonstrate that the impact of compressive ultralow frequency waves in the solar wind on the induced magnetospheres drive compressional, linearly polarized, magnetosonic ultralow frequency waves in the ionosphere, and a localized electromagnetic "ringing" at the local proton gyrofrequency. The pulsations heat and energize ionospheric plasmas. A preliminary survey of events shows that no special upstream conditions are required in the interplanetary magnetic field or solar wind. Elevated ion densities and temperatures in the solar wind near to Mars are consistent with the presence of an additional population of Martian ions, leading to ion-ion instablities, associated wave-particle interactions, and heating of the solar wind. The phenomenon was found to be seasonal, occurring when Mars is near perihelion. Finally, we present simultaneous multipoint observations of the phenomenon, with the Mars Express observing the waves upstream, and Mars Atmosphere and Voltatile EvolutioN observing the response in the ionosphere. When these new observations are combined with decades of previous studies, they collectively provide strong evidence for a previously undemonstrated atmospheric loss process at unmagnetized planets: ionospheric escape driven by the direct impact of transient phenomena from the foreshock and solar wind.

The MAVEN mission has measured an electron temperature spike at altitudes where the Martian atmosphere becomes optically thick and changes occur in the atmospheric chemistry. The temperature spike ...