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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.

Amongst various escape channels, ion outflow is a major contributor to atmospheric loss at Mars over geologic time. On Mars' nightside, observations have indicated that cusp regions within crustal magnetic fields are associated with phenomena such as accelerated particle populations, discrete auroral emissions, and ionospheric outflow; however, the kinetic physics occurring within crustal magnetic cusps is poorly understood. Here, we present 1.5-dimensional particle-in-cell simulations of magnetospheric-ionospheric interactions within martian crustal magnetic cusp regions of varying strength. Simulation results demonstrate the formation of quasi-static, field-aligned potentials pointing away from Mars that accelerate electrons into the martian atmosphere while accelerating ions away, thereby enhancing ionospheric escape. Escaping ionospheric flux scales with crustal field strength, with 160 nT crustal fields yielding >2× the ion escape flux than in the case with no crustal fields. We discuss these results andconclude that magnetic cusp regions may be significant sources of ion loss at Mars.

On day 138 of 2010, the plume of dust and gas emerging from Enceladus' South Polar Terrain passed between the Sun and the Cassini spacecraft. This solar occultation enabled Cassini's Ultraviolet Imaging Spectrograph (UVIS) and the Visual and Infrared Mapping Spectrometer (VIMS) to obtain simultaneous measurements of the plume's gas and dust components along the same lines of sight. The UVIS measurements of the plume's gas content are described in Hansen et al. (2011, GRL 38:11202) , while this paper describes the VIMS data and the information they provide about the plume's particle content. Together, the VIMS and UVIS measurements reveal that the plume material above Baghdad and Damascus sulci has a dust-to-gas mass ratio that is roughly an order of magnitude higher than the material above Alexandria and Cairo sulci. Similar trends in the plume's dust-to-gas ratio are also found in data obtained when Cassini flew through the plume in 2009, during which time the Ion and Neutral Mass Spectrometer (INMS), Radio and Plasma Wave Science instrument (RPWS) and Cosmic Dust Analyzer (CDA) instruments made in-situ measurements of the plume's gas and dust densities (Dong et al. 2015 JGR 120:915-937). These and other previously-published systematic differences in the material erupting from different fissures likely reflect variations in subsurface conditions across Encealdus' South Polar Terrain., 24 pages, 14 figures, submitted for publication in Icarus

Through phase-space mapping 6 yr of H+, O+, and O 2 + distributions measured in situ by the Mars Atmosphere and Volatiles EvolutioN (MAVEN) orbiter, we derive semiempirical average energetic neutral atom (ENA) distributions near Mars. Differential fluxes of H-ENAs and O-ENAs are estimated by line-integrating ENA production and loss rates in the average phase-space ion distributions. By repeating the procedure for a systematic series of vantage points, we produce synthetic ENA observations for virtual circular orbits with radii twice that of Mars, revealing the angular dependence of the observer’s position. Accounting for known ENA production and loss terms, we find that H+ in the upstream solar wind yields total antisunward H-ENA fluxes of ∼3 × 105 cm−2 s−1. The dayside magnetosheath produces H-ENA angular-differential fluxes of up to 3 × 105 cm−2 s−1 sr−1, while the magnetosheath flanks populate the planet’s nightside with H-ENA fluxes in the range of 104–105 cm−2 s−1 sr−1. The O-ENA environment is dominated by a near-isotropic ∼105 cm−2 s−1 sr−1 relatively low-energy (tens of eV) population originating in the top-side ionosphere, particularly on the dayside. Lower fluxes (103–104 cm−2 s−1 sr−1) of energetic O-ENAs (≳100 eV) are mainly found on the nightside and above the electric polar regions of the induced magnetosphere. Asymmetries in the ENA flow are largely limited to the energetic O-ENA populations, while the H-ENA distribution is mostly symmetric around the Sun‒Mars line. We discuss how synthetic ENA observations can provide insight into the near-Mars space environment, including the planet’s plasma environment and exosphere.

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.

We report the first global, time-dependent simulation of the Mars upper atmospheric responses to a realistic solar flare event, an X8.2 eruption on 10 September 2017. The Mars Global Ionosphere-Thermosphere Model runs with realistically specified flare irradiance, giving results in reasonably good agreement with the Mars Atmosphere and Volatile EvolutioN spacecraft measurements. It is found that the ionized and neutral regimes of the upper atmosphere are significantly disturbed by the flare but react differently. The ionospheric electron density enhancement is concentrated below ~110-km altitude due to enhanced solar X-rays, closely following the time evolution of the flare. The neutral atmospheric perturbation increases with altitude and is important above ~150-km altitude, in association with atmospheric upwelling driven by solar extreme ultraviolet heating. It takes ~2.5 hr past the flare peak to reach the maximum disturbance and then additional ~10 hr to generally settle down to preflare levels.

Much can be learned from terrestrial planets that appear to have had the potential to be habitable, but failed to realize that potential. Mars shows evidence of a once hospitable surface environment. The reasons for its current state, and in particular its thin atmosphere and dry surface, are of great interest for what they can tell us about habitable zone planet outcomes. A main goal of the MAVEN mission is to observe Mars’ atmosphere responses to solar and space weather influences, and in particular atmosphere escape related to space weather ‘storms’ caused by interplanetary coronal mass ejections (ICMEs). Numerical experiments with a data-validated MHD model suggest how the effects of an observed moderately strong ICME compare to what happens during a more extreme event. The results suggest the kinds of solar and space weather conditions that can have evolutionary importance at a planet like Mars.

We investigate a generation mechanism of O+ ion beams observed above the Martian bow shock by analyzing ion velocity distribution functions (VDFs) measured by the Suprathermal and Thermal Ion Composition instrument on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. In the solar wind near Mars, MAVEN often observes energetic O+ ion beams (similar to 10 keV or higher). Accompanied with the O+ ion beam events, we sometimes observe characteristic ion VDFs in the magnetosheath: a partial ring distribution. The partial ring distribution corresponds to pickup ions with a finite initial velocity (i.e., not newborn pickup ions), and its phase space density is much smaller than that of local pickup O+ ions of the magnetosheath. Thus, the partial ring distribution is most likely produced by the reflection of pickup O+ ions precipitating from the upstream solar wind below the bow shock. After being injected into the magnetosheath from the solar wind, the precipitating O+ ions are subject to the significantly enhanced magnetic field in this region and start to gyrate around the guiding center of the plasma frame in the magnetosheath. Consequently, a part of precipitating O+ ions are reflected back to the solar wind, generating O+ beams in the solar wind. The beams direct quasi-sunward near the subsolar region but have large angle with respect to the sunward direction at high solar zenith angles (>50 degrees). The reflected O+ beams are accelerated by the convection electric field of the solar wind and may escape Mars.

The accepted version of the above article was posted prematurely on September 11, 2015. The final version of record will be made fully available at later date along with a special collection of related papers.

We study the solar wind interaction with the Martian upper atmosphere during the 8 March 2015 interplanetary coronal mass ejection (ICME) by using a global multifluid MHD model. Comparison of the simulation results with observations from Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft shows good agreement. The total ion escape rate is increased by an order of magnitude, from 2.05 × 1024 s−1 (pre-ICME phase) to 2.25 × 1025 s−1 (ICME sheath phase), during this time period. Two major ion escape channels are illustrated: accelerated pickup ion loss through the dayside plume and ionospheric ion loss through the nightside plasma wake region. Interestingly, the tailward ion loss is significantly increased at the ejecta phase. Both bow shock and magnetic pileup boundary (BS and MPB) locations are decreased from (1.2RM, 1.57RM) at the pre-ICME phase to (1.16RM, 1.47RM), respectively, during the sheath phase along the dayside Mars-Sun line. Furthermore, both simulation and observational results indicate that there is no significant variation in the Martian ionosphere (at altitudes ≲ 200 km, i.e., the photochemical region) during this event.

The Mars Atmosphere and Volatile EvolutioN mission (MAVEN), launched on 18 November 2013, is now in its primary science phase, orbiting Mars with a 4.5 h period. In this study, we use a time-dependent MHD model to interpret plasma observations made by MAVEN particle and field instruments. Detailed comparisons between the model and the relevant plasma observations from MAVEN are presented for an entire Mars rotation under relatively quiet solar wind conditions. Through comparison along MAVEN orbits, we find that the time-dependent multispecies single-fluid MHD model is able to reproduce the main features of the plasma environment around Mars. Using the model results, we find that photoionization beyond the terminator is the dominant ion source as compared with day-night transport in maintaining the nightside ionosphere. Model results also show that both the time-varying solar wind conditions and the continuously rotating crustal field work together to control the ion escape variation with time.

International audience; We present a novel method to determine solar wind proxies from sheath measurements at Mars. Specifically, we develop an artificial neural network (ANN) to simultaneously infer seven solar wind proxies: ion density, ion speed, ion temperature, and interplanetary magnetic field magnitude and its vector components, using spacecraft measurements of ion moments, magnetic field magnitude, magnetic field components in the sheath, and the solar extreme ultraviolet flux. The ANN was trained and tested using 3 years of data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. When compared with MAVEN spacecraft's in situ measured values of the solar wind parameters, we find that the ANN proxies for the solar wind ion density, ion speed, ion temperature, and interplanetary magnetic field magnitude have percentage differences of 50% or less for 84.4%, 99.9%, 86.8%, and 79.8% of the instances, respectively. For the cone angle and clock angle proxies, 69.1% and 53.3% of instances, respectively, have angle differences of 30∘ or less.

International audience; We simulate and compare three phases of the Mars-solar wind interaction with the 8 March interplanetary coronal mass ejection (ICME) event using Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observations in order to derive heavy ion precipitation and escape rates. The MAVEN observations provide the initial conditions for three steady state MHD model cases, which reproduce the observed features in the solar wind density, velocity, and magnetic field seen along the MAVEN orbit. Applying the MHD results to a kinetic test particle model, we simulate global precipitation and escape maps of O+ during the (1) pre-ICME phase, (2) sheath phase, and (3) ejecta phase. We find that the Case 1 had the lowest precipitation and escape rates of 9.5 × 1025 and 4.1 × 1025 s−1, Case 2 had the highest rates of 9.5 × 1025 and 4.1 × 1025 s−1, and Case 3 had rates of 3.2 × 1025 and 1.3 × 1025 s−1, respectively. Additionally, Case 2 produced a high-energy escaping plume >10 keV, which mirrored corresponding STATIC observations.

International audience; We present the results of an initial effort to statistically map the fluxes of planetary ions on a closed surface around Mars. Choosing a spherical shell ~1000 km above the planet, we map both outgoing and incoming ion fluxes (with energies >25 eV) over a 4 month period. The results show net escape of planetary ions behind Mars and strong fluxes of escaping ions from the northern hemisphere with respect to the solar wind convection electric field. Planetary ions also travel toward the planet, and return fluxes are particularly strong in the southern electric field hemisphere. We obtain a lower bound estimate for planetary ion escape of ~3 × 1024 s−1, accounting for the ~10% of ions that return toward the planet and assuming that the ~70% of the surface covered so far is representative of the regions not yet visited by Mars Atmosphere and Volatile EvolutioN (MAVEN).

[1] There have been three Cassini encounters with the south-pole eruptive plume of Enceladus for which the Cassini Plasma Spectrometer (CAPS) had viewing in the spacecraft ram direction. In each case, CAPS detected a cold dense population of heavy charged particles having mass-to-charge (m/q) ratios up to the maximum detectable by CAPS (∼104 amu/e). These particles are interpreted as singly charged nanometer-sized water-ice grains. Although they are detected with both negative and positive net charges, the former greatly outnumber the latter, at least in the m/q range accessible to CAPS. On the most distant available encounter (E3, March 2008) we derive a net (negative) charge density of up to ∼2600 e/cm3 for nanograins, far exceeding the ambient plasma number density, but less than the net (positive) charge density inferred from the RPWS Langmuir probe data during the same plume encounter. Comparison of the CAPS data from the three available encounters is consistent with the idea that the nanograins leave the surface vents largely uncharged, but become increasingly negatively charged by plasma electron impact as they move farther from the satellite. These nanograins provide a potentially potent source of magnetospheric plasma and E-ring material.