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

Measurements provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft are analyzed to investigate the Martian magnetotail configuration as a function of interplanetary magnetic field (IMF) BY. We find that the magnetotail lobes exhibit a ~45deg twist, either clockwise or counterclockwise from the ecliptic plane, up to a few Mars radii downstream. Moreover, the associated cross-tail current sheet is rotated away from the expected location for a Venus-like induced magnetotail based on nominal IMF draping. Data-model comparisons using magnetohydrodynamic simulations are in good agreement with the observed tail twist. Model field line tracings indicate that a majority of the twisted tail lobes are composed of open field lines, surrounded by draped IMF. We infer that dayside magnetic reconnection between the crustal fields and draped IMF creates these open fields and may be responsible for the twisted tail configuration, similar to what is observed at Earth.

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.

An important mechanism in the generation of polar wind outflow is the ambipolar electric potential which assists ions in overcoming gravity and is a key mechanism for Terrestrial ionospheric escape. At Mars, open field lines are not confined to the poles, and outflow of ionospheric electrons is observed far into the tail. It has thus been hypothesized that a similar electric potential may be present at Mars, contributing to global ionospheric loss. However, no direct measurements of this potential have been made. In this pilot study, we examine photoelectron spectra measured by the Solar Wind Electron Analyzer instrument on the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) Mars Scout to put an initial upper bound on the total potential drop in the ionosphere of Mars of Φ♂≾⊥2V , with the possibility of a further ≾4.5 V potential drop above this in the magnetotail. If the total potential drop was close to the upper limit, then strong outflows of major ionospheric species (H+, O+, and O2+) would be expected. However, if most of the potential drop is confined below the spacecraft, as expected by current theory, then such a potential would not be sufficient on its own to accelerate O2+ to escape velocities, but would be sufficient for lighter ions. However, any potential would contribute to atmospheric loss through the enhancement of Jeans escape.

International audience; With electron and magnetic field data obtained by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we have identified closed magnetic field lines, with both foot points embedded in the dayside ionosphere, extending up to 6,200 km altitude into the Martian tail. This topology is deduced from photoelectrons produced in the dayside ionosphere being observed traveling both parallel and antiparallel to the magnetic field. At trapped-zone pitch angles (within a range centered on 90° where electrons magnetically reflect before interacting with the atmosphere), cases with either solar wind electrons or photoelectrons have been found, indicating different formation mechanisms for these closed loops. These large closed loops are present in MHD simulations. The case with field-aligned photoelectrons mixed with solar wind electrons having trapped-zone pitch angles is likely to be associated with reconnection, while the case with photoelectrons at all pitch angles is probably due to closed field lines being pulled tailward by the surrounding plasma flow. By utilizing an algorithm for distinguishing photoelectrons from solar wind electrons in pitch angle-resolved energy spectra, we systematically map the spatial distribution and occurrence rate of these closed magnetic loops over the region sampled by the MAVEN orbit. We find that the occurrence rate ranges from a few percent to a few tens of percent outside of the optical shadow and less than one percent within the shadow. These observations can be used to investigate the general magnetic topology in the tail, which is relevant to cold ion escape, reconnection, and flux ropes.

The crustal remnant field on Mars rotates with the planet at a period of 24 h 37 min, constantly varying the magnetic field configuration interacting with the solar wind. Until now, there has been no self-consistent modeling investigation on how this varying magnetic field affects the solar wind plasma interaction. Here we include the rotation of this localized crustal field in a multispecies single-fluid MHD model of Mars and simulate an entire day of solar wind interaction under normal solar wind conditions. The MHD model results are compared with Mars Global Surveyor (MGS) magnetic field observations and show very close agreement, especially for the field strength along almost all of the 12 orbits on the day simulated. Model results also show that the ion escape rates slowly vary with rotation, generally anticorrelating with the strength of subsolar magnetic crustal sources, with some time delay. In addition, it is found that in the intense crustal field regions, the densities of heavy ion components enhance significantly along the MGS orbit, implying strong influence of the crustal field on the ionospheric structures.

The 3-D multifluid Block Adaptive Tree Solar-wind Roe Upwind Scheme (BATS-R-US) MHD code (MF-MHD) is coupled with the 3-D Mars Thermospheric general circulation model (MTGCM). The ion escape rate from the Martian upper atmosphere is investigated by using a one-way coupling approach, i.e., the MF-MHD model incorporates the effects of 3-D neutral atmosphere profiles from the MTGCM model. The calculations are carried out for two cases with different solar cycle conditions. The calculated total ion escape flux (the sum of three major ionospheric species, O+, O2+, and CO2+) for solar cycle maximum conditions (6.6×1024 s−1) is about 2.6 times larger than that of solar cycle minimum conditions (2.5×1024 s−1). Our simulation results show good agreement with recent observations of 2–3×1024 s−1 (O+, O2+, and CO2+) measured near solar cycle minimum conditions by Mars Express. An extremely high solar wind condition is also simulated which may mimic the condition of coronal mass ejections or corotating interaction regions passing Mars. Simulation results show that it can lead to a significant value of the escape flux as large as 4.3×1025s−1.

[1] While the Mars upper atmosphere is continuously bombarded by charged particles of solar and planetary origins, the energy flux carried is often not sufficient to significantly affect the neutral atmosphere. However, we show that this is not the case during major space weather events. By applying two Mars global models—a Monte Carlo model for simulating pickup O+ precipitation at the exobase and a thermosphere-ionosphere model for assessing its global impact, we find that the thermospheric effects of reentering ions can change from negligible to very important when upstream solar wind conditions vary from normal to extreme. The atmospheric response under the most extreme conditions includes dramatic neutral temperature enhancement, significant neutral composition and wind changes, and increased importance of sputtering loss and possibly even thermal escape of heavy species.

[1] A 3D, multi-species, non-ideal MHD numerical code was used to calculate the ion escape fluxes from Mars. The calculations were carried out for six cases with different nominal solar wind, solar cycle and crustal field orientation conditions and the total escape fluxes (the sum of the three major ionospheric species, O+, O2+, and CO2+) varied by about an order of magnitude from 2.7 × 1023 to 2.4 × 1024 sec−1. These results were compared to the recently measured Mars Express results of 3.2 × 1023 sec−1 (O+, O2+, and CO2+), which were obtained near solar cycle minimum conditions, indicating a good agreement between measured and calculated fluxes. We also calculated the escape flux for “extremely” high solar wind conditions which leads to a flux of 3 × 1025 sec−1.

[1] The global features of the interaction between Saturn’s magnetospheric plasma flow and Titan’s atmosphere/ ionosphere are simulated by using a 3-D, multi-species, high spatial resolution, global MHD model. Our model uses a spherical grid structure leading to very good (36 km) altitude resolution in the ionospheric region of Titan. The model also provides good resolution and meaningful results in the upstream and wake regions. Titan’s atmosphere and ionosphere are approximated by 10 neutral and 7 ion species. Calculations, which make predictions for the anticipated results to be obtained by the Cassini spacecraft during its first close flyby (TA) of Titan, are presented. INDEX TERMS: 2427 Ionosphere: Ionosphere/ atmosphere interactions (0335); 2732 Magnetospheric Physics: Magnetosphere interactions with satellites and rings; 2753 Magnetospheric Physics: Numerical modeling. Citation: Ma, Y.-J., A. F. Nagy, T. E. Cravens, I. V. Sokolov, J. Clark, and K. C. Hansen (2004), 3-D global MHD model prediction for the first close flyby of Titan by Cassini, Geophys. Res. Lett., 31, L22803