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The Emirates Mars Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission spacecraft, which observes ultraviolet emission between approximately 100 and 170 nm, has observed multiple instances of nightside aurora at Mars. Variations in the auroral brightness and morphology have been observed to change on timescales of tens of minutes. The brightest aurorae are typically seen following space weather events, i.e., coronal mass ejection and stream interaction region impacts. The InSight Fluxgate Magnetometer (IFG) on the Interior Explorations using Seismic Investigations, Geodesy and Heat Transport (InSight) lander measured the magnetic field at the surface of Mars. IFG has measured variations in the nightside surface magnetic field, presumably due to variations in ionospheric and magnetospheric currents. Periodic and aperiodic variations in the surface field have been observed, including with timescales of a few minutes to tens of minutes. The magnitude of the fluctuations is often larger following space weather events. We examine the connection between the presence of aurora as observed by EMUS and surface magnetic field fluctuations as measured by IFG. Coincident EMUS and IFG observations show enhanced surface magnetic field fluctuations during times when aurorae were present. Additionally, the timescale of fluctuations in the auroral brightness are similar to the timescale of surface magnetic field fluctuations for non-coincident observations. These results suggest that IFG measured the surface magnetic field effect of time varying ionospheric auroral currents.

The Emirates Mars Mission (EMM) Hope probe launched on 20 Jul 2020 and entered Mars orbit on 9 Feb 2021, carrying a payload of 3 complementary instruments to characterize the global atmosphere across the full range of altitudes (surface to exosphere) at diurnal and seasonal timescales. The unique, high-altitude orbit of the Hope probe (19,970 km periapse, 42,650 km apoapse altitude, 25 deg inclination, 54.5-hour period) that enables its synoptic view of the red planet also brings the spacecraft across the orbit of Mars’ outermost moon, Deimos. The Hope trajectory was slightly modified by two maneuvers in Aug 2022 and Jan 2023 that will allow the surface of Deimos to be observed in a series of flybys in Feb-Mar 2023. Here we present preliminary results from the Emirates Mars Ultraviolet Spectrometer (EMUS), an imaging spectrograph with a wavelength range of 100-170 nm and a field of view of 10.75 x 0.18 deg (using the high-resolution slit position). We will derive the absolute reflectance of the surface, search for any compositionally distinct spectral features (e.g. carbon, polycyclic aromatic hydrocarbons, water ice), and examine any spatial heterogeneity across the surface.

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.

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.

Here we report on synoptic (or “disk”) observations of Martian discrete aurora in the extreme and far ultraviolet (

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.

Using Mars Atmosphere and Volatile EvolutioN (MAVEN) observations from 2014 to 2019, we characterize how the structure and composition of the nightside ionosphere varies on solar cycle and seasonal timescales. At fixed altitudes between 150 and 200 km, plasma densities vary substantially on these timescales in response to variations in fixed thermospheric pressure levels, which cause the ionosphere to rise and fall in altitude. Additionally, solar cycle and seasonal trends in the electron impact ionization (EII) rate affects nightside densities; higher densities are observed near solar maximum and Mars perihelion (when EII rates are largest), and lower densities are observed near solar minimum and Mars aphelion (when EII rates are smallest). Lastly, densities in the high-altitude ( > 200 km) nightside ionosphere vary significantly over the solar cycle: topside O + densities vary by a factor of ∼ 50 and topside O 2 + densities vary by a factor of ∼ 40. Topside ion densities were relatively stable throughout the solar minimum of 2018–2019.

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

Understanding and predicting processes that perturb planetary ionospheres is of paramount importance for long-distance radio communication. Perhaps the oldest known ionospheric disturbances are ‘sporadic E layers’1: unpredictable and short-lived concentrations of plasma2, which can bounce radio signals over the horizon for thousands of kilometres3. Consequentially, local radio broadcasts can become jammed by more distant transmissions, and thus sporadic E layers are a potentially serious complication for commercial radio, aviation, shipping or the military. According to the current theory of their formation, we should also expect an equal proportion of localized ionospheric density depletions to develop. However, no such ‘sporadic E rifts’ have been detected in over 85 years of ionospheric research. In addition, despite being common at Earth, no sporadic E layers have yet been reported at other planets. Here we report the detection of sporadic E-like phenomena in the ionosphere of Mars by NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, providing a physical explanation for previous unexplained observations at Mars4–7. We observe enhanced-density layers that can be explained through the presence of a sporadic E-like mechanism, and we establish the existence of sporadic E rifts in nature. We find that, unlike the case at Earth, Martian sporadic E features are trapped in a near-perpetual state of dynamic formation and may form at predictable locations. Also unlike the case at Earth, Martian sporadic E features are readily accessible to satellites, and indeed MAVEN has already encountered more of the phenomena at Mars than have ever been explored in situ at Earth with suborbital rockets. Sporadic E layers are unpredictable terrestrial ionospheric phenomena that can perturb telecommunication. Plasma features akin to sporadic E layers and their opposite (sporadic E rifts), never observed on Earth, were detected in the ionosphere of Mars from MAVEN data. In contrast to those observed on Earth, they are long lived and form at predictable locations.

The Emirates Mars Mission (EMM) Hope probe was launched on 20 July 2020 at 01:58 GST (Gulf Standard Time) and entered orbit around Mars on 9 Feb 2021 at 19:42 GST. The high-altitude orbit (19,970 km periapse, 42,650 km apoapse altitude, 25° inclination) with a 54.5 hour period enables a unique, synoptic, and nearly-continuous monitor of the Mars global climate. The Emirates Mars Ultraviolet Spectrometer (EMUS), one of three remote sensing instruments carried by Hope, is an imaging ultraviolet spectrograph, designed to investigate how conditions throughout the Mars atmosphere affect rates of atmospheric escape, and how key constituents in the exosphere behave temporally and spatially. EMUS will target two broad regions of the Mars upper atmosphere: 1) the thermosphere (100–200 km altitude), observing UV dayglow emissions from hydrogen (102.6, 121.6 nm), oxygen (130.4, 135.6 nm), and carbon monoxide (140–170 nm) and 2) the exosphere (above 200 km altitude), observing bound and escaping hydrogen (121.6 nm) and oxygen (130.4 nm).EMUS achieves high sensitivity across a wavelength range of 100–170 nm in a single optical channel by employing “area-division” or “split” coatings of silicon carbide (SiC) and aluminum magnesium fluoride (Al+MgF2) on each of its two optical elements. The EMUS detector consists of an open-face (windowless) microchannel plate (MCP) stack with a cesium iodide (CsI) photocathode and a photon-counting, cross-delay line (XDL) anode that enables spectral-spatial imaging. A single spherical telescope mirror with a 150 mm focal length provides a 10.75° field of view along two science entrance slits, selectable with a rotational mechanism. The high and low resolution (HR, LR) slits have angular widths of 0.18° and 0.25° and spectral widths of 1.3 nm and 1.8 nm, respectively. The spectrograph uses a Rowland circle design, with a toroidally-figured diffraction grating with a laminar groove profile and a ruling density of 936 gr mm−1 providing a reciprocal linear dispersion of 2.65 nm mm−1. The total instrument mass is 22.3 kg, and the orbit-average power is less than 15 W.

To date, Mars’s weather has been monitored mainly from spacecraft in polar or quasi-polar orbits, which sample only a narrow range of local times, or several local times over multiple sols with discontinuous spatial coverage (Fig.1). When observations have been made and/or analyzed at different local times, a high magnitude of diurnal variability often has been found [see e.g. 1 to 5]. The significance of diurnal meteorological variability at Mars argues for orbital observations that span the diurnal cycle. The rapid dynamics of meteorological phenomena such as dust storms (typical timescale of a few hours) and water/CO2 ice clouds (typical timescale of half an hour or less), together with their spatial extension (up to the planetary scale for dust events) and duration/repeatability, argues for continuous and simultaneous observations across the planet (Fig.1). As it happened for the study of meteorology on Earth in the 1970s, now is the right time to introduce monitoring to the observation paradigm for the martian atmosphere, so far almost exclusively focused on mapping. The Emirates Mars Mission (EMM), which entered Mars’s orbit in February 2021, is the first orbiter fully dedicated to the study of its climate. Thanks to its high, eccentric, low inclination orbit, it is also the first satellite that can reasonably observe the evolution of meteorological phenomena over multiple local times simultaneously, thus operating the transition from the mapping to the monitoring paradigm. Although unique so far, EMM alone cannot provide what has been identified as a high priority requirement to improve the spatiotemporal coverage of existing data and to enable future human exploration missions, i.e. global, continuous, and simultaneous monitoring, leading to forecasting of meteorological phenomena [6]. Quasi-global monitoring (excluding the polar regions) can be achieved by a constellation of areostationary platforms, i.e. satellites in equatorial, circular orbits in which the orbital period of the satellite matches the rotational period of Mars. The minimum number required for covering all equatorial longitudes is three [7]. The required number to cover all longitudes in a continuous latitude band extending from nearly 80°S to nearly 80°N with some large overlapping in longitude is four (Fig.2). If the areostationary constellation is coupled with at least one satellite in low polar orbit, the continuous (high cadence) and simultaneous (all locations at once) monitoring becomes nearly global [8]. Areostationary observations would revolutionize Mars weather forecasting as geostationary satellite imagery did for Earth weather forecasting in the 1970s. The quasi-global, continuous, and simultaneous view that observations from an areostationary network provide would allow forecast initialization from atmospheric states that properly account for teleconnections, large-scale weather and dust events, tides, and other diurnally varying, global-scale phenomena (Fig. 3). Operational monitoring coupled to modelling will enable forecasting, allowing to take preventive actions and minimize risks. It will take several attempts to optimize an operational monitoring and forecasting system, primarily because extreme events such as dust storms attaining the planetary scale occur at irregular times. It is thus essential to send precursor missions aimed at developing the operative infrastructure well in advance of the first human mission. Areostationary platforms do not only offer advantages in meteorology. Satellites in areostationary orbit would spend nearly 75% of their time outside the bow shock of Mars, offering monitoring of the upstream solar wind at an unobstructed vantage point (Fig. 4). The high distance of an areostationary orbit from Mars could also allow for globally mapping the escape of atmospheric species in response to changes in upstream drivers, a task only partially fulfilled by EMM. Last but not the least, areostationary relay satellites could advance telecommunication capabilities for future robotic and human Mars missions far beyond current capabilities [9 to 11]. They are also ideal to support the communication requirements of a future generation of small, low-cost Mars science orbiters and be part of a Global Navigation Satellite System (GNSS), which would greatly improve mission safety and reliability for sustainable, long-term exploration [12]. See [7] for more information on the benefits and applications of satellites in areostationary orbit. Furthermore, the architecture of the constellation, and recent advancements on on-board computational capabilities, would enable significant degrees of autonomy, such as coordination of observations, event-driven operations, and goal-based monitoring. In order to fully shift paradigm from mapping to monitoring, therefore, we have developed a mission concept to send a constellation of at least three satellites in the second half of the current decade, place them in an areostationary orbit, and monitor atmospheric and space weather over the course of at least two Martian years. We name our concept MACAWS, which stands for "Monitoring Areostationary Constellation for Atmosphere and Weather in Space" (Fig. 5). The nature and objectives of this novel mission lend themselves to the use of SmallSats to reduce costs and accept higher risks, while maximizing impact. The scientific and operational achievements of this precursor mission will directly feed into the subsequent planning of larger-scale monitoring constellations. The stated goal of MACAWS is to be a low-cost, precursor, orbital mission to monitor atmospheric and space weather events continuously and simultaneously at most locations on the planet and in the upstream solar wind, in preparation for the human exploration of Mars. The scientific payload, mission architecture, and ConOps are defined accordingly (Fig. 6). The planned outcomes are a better scientific understanding of the dynamics of such events, and the development of an operational forecasting system in order to reduce the risks for humans when in orbit around Mars or on the ground. REFERENCES [1] Glenar+ 2003 Icarus 161 297, https://doi.org/10.1016/S0019-1035(02)00046-5 [2] Zent+ 2016 JGR Plan. 121 626, https://doi.org/10.1002/2015JE004933 [3] Wolkenberg & Giuranna 2020 Icarus 113823, https://doi.org/10.1016/j.icarus.2020.113823 [4] Kleinboehl+ 2020 JGR Plan., e2019JE006115, https://doi.org/10.1029/2019JE006115 [5] Montabone+ 2020 JGR Plan., e2019JE006111, https://doi.org/10.1029/2019JE006111 [6] Banfield+ 2020 MEPAG Science Goals, https://mepag.jpl.nasa.gov/reports/MEPAGGoals_2020_MainText_Final.pdf [7] Montabone+ 2020 White Paper PSA Decadal Survey, https://bitly.com/areowhitepaper [8] Lillis+2021, Planet. Sci. J., in press [9] Breidenthal+2018 SpaceOps Conf. 2426, https://doi.org/10.2514/6.2018-2426 [10] Edwards+2016 Proc. IEEE Aerosp. Conf., https://doi.org/10.1109/AERO.2016.7500680 [11] Lock+2016 Proc. IEEE Aerosp. Conf., https://doi.org/10.1109/AERO.2016.7500899 [12] Pirondini & Fernandez 2003 ESA Executive Summary, https://esamultimedia.esa.int/docs/Aurora/execsummaries/Interplanetary_GNSS.pdf

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.

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.

National Natural Science Foundation of China [41525015, 41774186, 41525016]; Science and Technology Development Fund of Macau SAR [039/2013/A2, 119/2017/A3]; National Aeronautics and Space Administration (NASA); Swedish National Space Agency [135/13, 166/14]; Swedish Research Council (VR grant) [621-2013-4191]

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 Thalassa mission concept was developed in response to the 2019 NASA Planetary Mission Concept Studies call. Using a multi-platform mission architecture, Thalassa seeks to address a single science goal: to determine the extent to which water has played a role in the geological evolution of Venus.

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.

International audience; Crustal magnetic fields influence a range of plasma processes at Mars, guiding the flow of energy from the solar wind into the planet's atmosphere at some locations while shielding the atmosphere at others. In this study we investigate how the topology of crustal fields varies with changes in the direction of the incoming interplanetary magnetic field (IMF). Using plasma measurements from Mars Atmosphere and Volatile Evolution (MAVEN) and Mars Global Surveyor (MGS), we identify magnetic topology throughout the Martian ionosphere and perform a statistical analysis of crustal magnetic field topology during different IMF configurations. We find that the topology of crustal field cusp regions is dependent on IMF direction and that cusps transition between open and closed topology regularly as they rotate through the nightside of Mars. Finally, we determine that cusps often become topologically closed due to reconnection with open magnetic fields in the Martian magnetotail, creating large closed loops that connect the dayside and nightside of Mars.

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.

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.

With both the Mars Atmosphere and Volatile Evolution (MAVEN) mission and the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission concurrently operating at Mars, we are able to make two point comparisons of the vector magnetic field at Mars for the first time. During MAVEN overflights of the InSight landing site, we compared deviations in the ionospheric magnetic field to variations in the surface level magnetic field. We find significant orbit to orbit variability in the magnitude and direction of the ionospheric magnetic field as well as significant day to day variability of the surface level magnetic field. We attribute this variability to time varying ionospheric currents. However, when analyzing the ensemble of 16 individual MAVEN overflights of the InSight landing location, we see no clear correlation between the magnitudes or directions of the ionospheric magnetic field and the surface magnetic field as might be expected. If the presumed ionospheric currents have a small scale size, then the ionospheric magnetic field will display increased variability as MAVEN flies through the current structure. Whereas the present analysis is restricted to mostly nightside MAVEN overflights where current are expected to be weak, future analyses should incorporate dayside overflights where current are expected to be stronger and current signatures more clear.

As Mars has no intrinsic magnetic field, it is inherently strongly influenced by the solar wind. However, little is known about the scale of variability of the solar wind at this distance from the Sun. The lack of an upstream solar wind monitor at Mars sometimes necessitates assumptions about the variability of solar wind and interplanetary magnetic field (IMF) conditions at Mars, and without a clear understanding of how the solar wind varies at Mars it is difficult to know whether these assumptions are appropriate. We present a study which quantifies the variation of the IMF at Mars during periods near solar maximum and minimum, by comparing magnetometer measurements of the pristine IMF from the Mars Global Surveyor (MGS) mission (between 1997 and 1999) and the MArs Volatile EvolutioN (MAVEN) mission (between 2014 and 2016). This study finds the IMF to be notably steadier in field strength and cone angle direction during the MAVEN mission than the MGS mission (shown in Figures 1 and 2), with little difference in the clock angle variation between the two missions. Additionally, the variability of both the field strength and the clock angle is found to be dependant on the cone angle of the measurements, with periods of IMF oriented close to the orbital plane of Mars being considerably steadier than periods of IMF oriented approximately perpendicular to it. Results from this study suggest that the IMF at Mars is steadier at times near solar maximum than at times near solar minimum, and quantify the error in estimates of IMF parameters hours after measurement. However, using solar 10.7cm flux as a proxy for solar activity, we show that the time for the IMF to decorrelate does not directly depend on the solar activity. Figure 3 shows the decorrelation time and the solar activity for both the MGS and MAVEN datasets. No clear correlation is visible in the graphs, suggesting that the reason for the differences in the IMF variability between the two missions is still unclear.

The Martian atmosphere (from the surface up to the outer layers) is a very dynamic system, quickly responding to strong radiative forcing coming from the absorption of solar radiation from dust particles lofted during dust storms. So far, such dynamical phenomena at short time scales and large spatial scales have been observed mainly from spacecraft in polar or quasi-polar orbits, which cannot provide continuous and simultaneous observations over fixed, large regions. This limitation can be bypassed using spacecraft in equatorial, circular, planet-synchronous (i.e. areostationary) orbit at an altitude of 17,031.5 km above the Martian surface. Besides their possible use as communication relays for ground-based assets, for space weather monitoring (they orbit outside Mars' bow shock), and for the study of surface properties (e.g. thermal inertia and albedo), the unique scientific advantages of areostationary satellites for weather monitoring are comparable to those provided by geostationary satellites. These platforms greatly increase the temporal resolution and coverage of single events, and are ideally suited for data assimilation in global climate models. Thanks to NASA PSDS3 program, we have elaborated a mission concept to put a low-cost, low-weight, ESPA-class SmallSat in areostationary orbit, which is capable of supporting various tank sizes in order to provide a wide range of ΔV for three different Mars arrival scenarios. ExoTerra Resource LLC adapted its "Electrically Propelled Interplanetary CubeSat" bus as part of the mission design. Despite the optimization of the flight trajectories and the use of machine learning algorithms to prioritize data downlink, the conclusions of the concept study clearly point towards the current challenges represented by propulsion, communication, and possibly radiation tolerance for scientific SmallSat missions to Mars. Such conclusions are generally common among all low-cost interplanetary SmallSat concepts. Furthermore, a single areostationary satellite is enough to provide a full-disk view to monitor regional dust storms and water ice clouds at specific locations, but cannot provide the global coverage required to understand extreme phenomena such as Martian planetary-scale dust events. For this reason, we have recently started to study a more advanced mission concept involving the use of at least three areostationary satellites. This new study is carried out in collaboration with the Jet Propulsion Laboratory within the scope of a wider NASA-funded project (PMCS program) looking at a constellation concept. The challenge is to keep the areostationary satellite configuration within the ESPA class limits, in order to take advantage of possible future rideshare opportunities.

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.