Poster presentations and abstracts

Introduction

Comets are unique objects. Due to their varying distance to the Sun, and the resulting variation of the plasma environment, they provide a unique opportunity to study plasma processes and an objects interaction with the solar wind. The comet’s neutral coma is ionized through photoionization, electron impact ionization and charge exchange, creating a comet ionosphere. The newly born ions are initially cold and flowing with the neutral gas, but are eventually accelerated by the convective electric field of the solar wind and are incorporated into the solar wind flow, a process often referred to as mass loading. The solar wind is as a consequence slowed down and deflected, leading to the creation of a bow shock, a cometopause and, closest to the comet nucleus, a magnetic field free region. This region is known as the diamagnetic cavity.

The diamagnetic cavity is filled with newly born low-energy ions. Pick up processes are unimportant in this region; instead the ions are accelerated radially outwards due to an ambipolar electric field. Also important in this region is the interaction with the neutral particles. After the visit of Giotto to comet 1P/Halley it was suggested that the collisional coupling of the ions to the neutrals is dominating in this region (e.g. Cravens, 1989), making the ions flow with the same velocity as the neutrals. The resulting ion-neutral drag force was suggested to be the force balancing the outside magnetic pressure at the contact surface. This picture may, however, have to be revised after Rosetta’s visit to comet 67P/Churyumov-Gerasimenko. Measurements indicate that the ions may not be coupled to the neutrals. Odelstad et al. (2018) found ion velocities in the diamagnetic cavity of 2-4 km/s, which is above the expected velocity of the neutral particles (<1 km/s). Vigren et al. (2017) estimated ion velocities of 2-8 km/s near perihelion, and modelling efforts by Vigren & Eriksson (2017) show that the strength of the ambipolar field is sufficient to, at least partly, decouple the ions from the neutrals. Further studies of the low-energy ions in this region is, however, necessary to establish the physical processes governing this region.

The Ion Composition Analyzer (ICA, Nilsson et al., 2007) on board Rosetta was measuring ions down to energies of just a few eV. The substantially negative spacecraft potential of Rosetta has, however, distorted the low-energy data, which has therefore not been fully exploited. In recent studies by Bergman et al. (2020a,b), the influence of the spacecraft potential has, however, been modelled, making it possible to study the low-energy ions in more detail. In the current study we aim to use the method developed by Bergman et al. (2020a,b) to estimate the bulk velocity, temperature and flow direction of the low-energy ions observed by ICA inside the diamagnetic cavity.

Method

Data

ICA is a mass resolving ion spectrometer, measuring the three-dimensional distribution function of positive ions within an energy range of a few eV/q to 40 keV/q. The nominal FOV is 360ºx90º, and the time resolution is 192 seconds. During the mission ICA was occasionally run in a mode with a higher time resolution of 4 seconds. In this mode, the instrument is measuring in 2D and only sweeps over the lowest energies (up to ~80 eV). Fast changes in the low-energy ion environment can then be captured. In this study, we only use data obtained with this high time resolution mode. In total ~80 events of high time resolution data have been obtained by ICA inside the diamagnetic cavity. One energy-time spectrogram is, as an example, shown in Figure 1.

Simulations

We use the Spacecraft Plasma Interaction Software (SPIS, Thiébault et al., 2013), and the method developed by Bergman et al. (2020a,b), to model the distortion of the velocity distribution of the low-energy ions, caused by the negatively charged spacecraft. The principle is illustrated in Figure 2. From an initially Maxwellian velocity distribution with bulk velocity v and temperature T, the model provides a resulting detected energy distribution and a flux distribution over the azimuthal sectors of the instrument. By comparing the model results for different bulk velocity-temperature combinations to the ICA data, conclusions can be drawn about the initial velocity distribution of the detected ions.

Expected Results

In this presentation, we will show the most probable bulk speeds and temperatures of the low-energy ions inside the diamagnetic cavity, as estimated from the ICA data. We will also use the simulation results from Bergman et al. (2020a,b) to estimate the flow direction of the ions.

Acknowledgements

The work of S. Bergman is supported by the Swedish National Space Agency through grant 130/16.

References

Bergman, S. et al. (2020a). JGR: Space Physics, 125. doi: 10.1029/2019JA027478

Bergman, S. et al. (2020b). JGR: Space Physics, 125. doi: 10.1029/2019JA027870

Cravens, T. (1989). JGR, 94(A11). doi: 10.1029/JA094iA11p15025

Nilsson, H. et al. (2007). Space Science Reviews, 128. doi: 10.1007/s11214-006-9031-z

Odelstad, E. et al. (2018). JGR: Space Physics, 123. doi: 10.1029/2018JA025542

Thiébault, B. et al. (2013). SPIS 5.1 User Manual.

Vigren, E. & Eriksson, A. (2017). The Astronomical Journal, 153. doi: 10.3847/1538-3881/aa6006

Vigren, E. et al. (2017). MNRAS, 469. doi: 10.1093/mnras/stx1472

How to cite: Bergman, S., Stenberg Wieser, G., Wieser, M., Nilsson, H., Williamson, H., Nemeth, Z., and Johansson, F.: Low-energy ion bulk velocities and temperatures inside the diamagnetic cavity of comet 67P, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-282, https://doi.org/10.5194/epsc2020-282, 2020.

A useful property of the direction of the ion velocity vectors measured across the Venus wake is that they retain a nearly unchanged configuration; that is, the flow orientation maintains an orderly distribution. Evidence to support this view is provided by the flow pattern presented in the top left panel of Figure 1. The average velocity vectors of the planetary O+ ions collected in several orbits of the VEX spacecraft remain well organized along the tail with some of them displaying a common deflection towards the Y axis. That pattern is entirely different from the erratic distribution of the magnetic field vector orientation presented in the top right panel of that figure. The varying direction of the magnetic field vectors differs from the well organized orientation of the velocity vectors which thus is not influenced by changes of the magnetic field direction; namely, their orientation is not dependant on the J x B force. Their direction of motion is subject to a combination of the solar wind aberration force and the Magnus force along the Y-axis as indicated in the top  left panel of Figure 1. As a result the direction of the velocity vectors of the planetary ions is not solely controlled by the J x B force. Other forces mostly derived from wave-particle interactions are necessary to justify the organized distribution of the velocity vectors of the streaming flow. The data presented here thus provide an important source of information regarding the orderly direction of the ion velocity vectors along the tail which is unrelated to the J x B force.

A general displacement of the velocity vectors of the solar wind in the Venus wake in the southbound direction is illustrated in the bottom panel of Figure 1. Measurements conducted with the ASPERA instrument show an overall tendency for the flow to shift towards the –Z  direction as it has been reported from the data obtained in several VEX orbits (Perez-de-Tejada and Lundin (EPSC-DPS 2019 – 184-1,Vol. 13. 2019),

The tendency of the vortex structure to shift to lower negative Z values with increasing X distances downstream from Venus is more noticeable in orbits approaching maximum conditions of the solar cycle. A comparable difference is also measured in the different width values of the vortex structures becoming smaller during solar cycle maximum conditions.

Figure 1. Average values of the planetary O+ velocity vectors (top left panel) and the magnetic field vectors (top right panel) measured with the VEX spacecraft along the Venus tail. The direction of the velocity vectors exhibits an orderly configuration while the magnetic field vectors become erratic. Red and blue arrows correspond to Z > 0 and Z < 0 locations.  (Bottom panel) Schematic view of the corkscrew shape in the distribution of average values of velocity vectors of planetary O+ ions inferred from measurements in several VEX orbits as the ions move downstream from Venus.

How to cite: Pérez-de-Tejada, H. and Lundin, R.: Velocity vectors in the Venus wake unrelated to the J x B force, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-63, https://doi.org/10.5194/epsc2020-63, 2020.

Abstract

The escape of atmospheric particles to space is an important process to understand the evolution of planetary atmospheres. Venus is thought to have lost a large part of its water content to space throughout its history. The escape to space is inherently coupled with the interaction between the planet and the solar wind, and how much energy and momentum that are transferred from the solar wind to the escaping particles. In this study, we determine how much solar wind power is transferred to the ionospheric plasma that escape to space. We also investigate how the transfer coefficient depends on solar wind conditions.

1. Introduction

Today, the Venusian atmosphere is massive and contains only tiny amounts of water. However, measurements indicate that the atmosphere contained a significant amount of water in its early history [e.g.  9]. Several processes are capable of removing water from Venus atmosphere, which can be summarised into two main parts: (1) interaction between surface and atmosphere, and (2) escape of atmospheric constituents to space. In this study, we focus on the second process.

We investigate how non-thermal escape of O⁺ is affected by the upstream solar wind (SW) conditions. As the SW flows past Venus, some of its energy and momentum are transferred to the upper atmospheric particles [e.g. 3, 4]. The additional momentum allows the upper atmospheric O⁺ ions to reach above escape energy (~8 eV) and escape the planet [e.g. see review in 2]. An increase in the available energy in the upstream SW was shown to increase the total O⁺ escape in the magnetotail [5]. However, to fully characterise the interaction between the SW and the ionosphere, the efficiency of the coupling between them is important to determine.

In this study, we compare the available power in the upstream SW that can potentially reach the ionosphere, with the power escaping the atmosphere in the form of O⁺ ions in the magnetotail, to address the efficiency of the energy transfer.

2. Data

We use the full dataset from 2006-2014 of the Ion Mass Analyser (IMA), part of the Analyser of Space Plasmas and Energetic Atoms (ASPERA-4) instrument onboard Venus Express (VEx). The IMA instrument has the capability to measure ions of energy 0.01-36 keV/charge, with a total field-of-view of 90x360˚, where the resolution is 5.6x22.5˚. The moderate mass separation capability of IMA allows to efficiently separate the heavier species from the lighter. For details see [1].

3. Method

We calculate the escape rate by systematically combining O⁺ distribution functions in the magnetotail to create average ion distributions. The distributions are combined with respect to spatial location and upstream SW conditions (solar wind energy flux (SWEF) and solar extreme ultraviolet (EUV) radiation flux).

The upstream SWEF is measured during time periods when VEx was located outside the bow shock [6]. The SWEF is separated into 5 bins, where each is separated into high and low EUV flux. The EUV flux is propagated from measurements at Earth [see details in 5, 6]. The average distributions made for each of the ten upstream conditions are then integrated spatially over the magnetotail to calculate the total average escape rate for each condition [5].

The coupling between the upstream SW and the escape rate is calculated as the ratio of their respective powers. The SW power is calculated as SWEF multiplied by the area over which energy and momentum can be transferred. Here we assumed the size of the interaction area to be the induced magnetosphere boundary at the terminator. The escape power is calculated as an integration of the differential energy flux of the escaping ions. The ratio indicates how efficient the energy transfer is from the SW to the ionosphere and the escaping ions.

4. Results & discussion

The results show that the coupling efficiency decreases as the available power in the SW increases. Even though there is an increase in the number of ions escaping with an increased available energy [5], there is a smaller fraction of the available energy that is transferred.

On average only ~0.008 % of the SW power is transferred to the escaping ions. This indicates that the Venusian plasma environment actively and efficiently screens the ionosphere from the SW. The induced magnetosphere is capable of diverting the majority of the incoming SW energy and momentum, and divert the flow around itself, rather than absorbing it.

We can compare the coupling coefficient at Venus with that at Mars and Earth. The average coupling coefficient at Mars was found as ~0.67 % [7], which is a factor ~100 times higher than that at Venus. This may in part be due to that the induced magnetosphere of Venus is larger than that of Mars, which means that the amount of available energy that can be transferred to the induced magnetosphere is larger. The average escape rates are also comparable with ~2·10²⁴ s^-1 at Mars [6], and (3-6) ·10²⁴ s^-1 at Venus [2]. Therefore, the coupling coefficient is smaller at Venus than at Mars.

At Earth, the coupling was shown to increase as the available power upstream increased, after a threshold was reached [8]. Earth, with its magnetosphere, has a completely different interaction with the SW, compared to the induced magnetospheres of e.g. Venus and Mars. The difference in the coupling between the SW and the escape from Earth and Venus (and Mars) indicates that an intrinsic magnetic field does not provide better protection against SW erosion than an induced magnetosphere.

Acknowledgements

M. Persson acknowledges support of her graduate studies from SNSA (Dnr: 129/14).

References

[1] Barabash, et al. (2007). PSS, 10.1016/j.pss.2007.01.014

[2] Futaana, et al. (2017). Sp. Sci. Rev., 10.1007/s11214-017-0362-8

[3] Lundin, et al. (2011). Icarus, 10.1016/j.icarus.2011.06.034

[4] Perez-de-Tejada, (1986). JGR: 91.A6, pp. 6765–6770

[5] Persson, et al. (2020). JGR, 10.1029/2019JE006336

[6] Ramstad, et al. (2015). JGR, 10.1002/2015JE004816

[7] Ramstad, et al. (2017). JGR, 10.1002/2017JA024306

[8] Schillings, et al. (2019). EPS, 10.1186/s40623-019-1048-0

[9] Way, et al. (2016). GRL. 10.1002/2016GL069790

How to cite: Persson, M., Futaana, Y., Ramstad, R., Masunaga, K., Nilsson, H., Fedorov, A., and Barabash, S.: Global Venus-solar wind coupling and oxygen ion escape, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-344, https://doi.org/10.5194/epsc2020-344, 2020.

The physics of the interaction of unmagnetized planets with the Solar wind has
been investigated since the first Mariner spacecraft did reach Mars and Venus
more than 50 years ago. Recent observations of the magnetic fields at Mars allowed 
to derive the global electric current configuration in the Martian system.
Earlier magneto hydro-dynamic models were able to predict the formation
and location of the bowshock in front of the planets. More sophisticated models 
of the interaction with the magnetized solar wind later could demonstrate
the global static picture of the plasma environment of Mars and Venus. But earlier models were rarely
able to model dynamic effects and the timing of physical process in this interaction.
We here use the open source PLUTO code in its 3D spherical hydrodynamic and magneto-hydrodynamic version. 
We also develop a multi-species extension of this code. 
We investigate the interaction of the solar wind with the ionospheres of Mars and Venus with the aim to understand the 
importance of  different physical effects on bow shock location, ion escape and specifically the electric current structures. 
We compare these simulations to observations by the VEX and MAVEN spacecraft.

How to cite: Fränz, M., Dubinin, E., and Maes, L.: Electric current systems at Mars and Venus, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1017, https://doi.org/10.5194/epsc2020-1017, 2020.

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.

How to cite: Fowler, C., Agapitov, O., Xu, S., Mitchell, D., Andersson, L., Artemyev, A., Espley, J., Ergun, R., and Mazelle, C.: 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, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-463, https://doi.org/10.5194/epsc2020-463, 2020.

Mirror mode (MM) structures have been evidenced everywhere in solar system plasmas, from the solar wind to Earth, Mars and Venus, as well as comets. MM waves are low-frequency long-wavelength transverse waves, usually linearly polarised and non-propagating in the plasma rest frame. In the data they commonly appear as sudden dips or peaks in the magnetic field intensity, anti-correlated with plasma density variations. They grow in a high-β plasma from an ion temperature anisotropy itself triggered by any asymmetry upstream in the solar wind flow, or typically as a result of the crossing of a quasi-perpendicular bow shock.

We present here statistical maps of MM waves detected by magnetic-field-only measurements as observed by the NASA/MAVEN spacecraft and its fluxgate magnetometer MAG. Candidate detections are validated against high-cadence plasma moments given by the Solar Wind Ion Analyzer (SWIA) to yield the best set of B-field-only criteria. We examine the dependence of these MM structures on Martian Year (MY, see figure), season (solar longitude Ls) and solar activity (EUV flux). They appear to be bound by the bow shock on one side and by the magnetic pile-up boundary on the other. Occurrence probability is less than 6% on average at any time. Distribution qualitatively agrees with previous studies with a smaller data subset.

The figure shows B-field-only candidate detections for MM waves at Mars, MY32 to MY35 (with ΔB/B ≥ 0.25, and the angles to the minimum/maximum variance direction Φ_minV ≥ 80° and Θ_maxV ≤ 20°).

How to cite: Simon Wedlund, C., Volwerk, M., Mazelle, C., Möstl, C., Rojas-Castillo, D., Espley, J., and Halekas, J.: On Mirror Mode Waves at Mars: Results from MAVEN, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-777, https://doi.org/10.5194/epsc2020-777, 2020.

We report on the local structure of the Martian subsolar Magnetic Pileup Boundary (MPB) from minimum variance analysis of the magnetic field measured by the MAVEN spacecraft for six orbits. In particular, we detect a well defined current layer within the MPB’s fine structure and
provide a local estimate of its current density and compare these results with the current density obtained by multi-fluid simulations.
This current is of the order of hundreds of nAm^-2 which results in a sunward Lorentz force of the order of 10^-14 Nm^-3. We compare these results with multifluid numerical simulations.
This force is associated with the gradient of the magnetic pressure, it accounts for the deflection of the solar wind ions near the MPB and for the acceleration of solar wind electrons which carry the interplanetary magnetic field through the MPB into the MPR. We also find that the
thickness of the MPB current layer is of the order of both the upstream (magnetosheath) solar wind proton inertial length and convective gyroradius. The former is consistent with the demagnetization of the ions due to the Hall electric field, an effect observed recently at the Earth magnetopause, while the latter would imply kinetic processes are important at the MPB.
This study supports recent results that report the presence of a steady current system around Mars in a similar way to the Earth.

How to cite: Boscoboinik, G., Bertucci, C., Gomez, D., Morales, L., Mazelle, C., Regoli, L., Halekas, J., Gruesbeck, J., Mitchell, D., and Jakosky, B.: The fine structure of the subsolar MPB current layer from MAVEN observations: Implications for the Lorentz force, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-985, https://doi.org/10.5194/epsc2020-985, 2020.

The study of the structure of the Martian shock is crucial to understand its microphysics and it is of special interest to understand the solar wind interaction with an unmagnetized, atmospheric body. 

The Martian bow shock is a rich example of a supercritical, mass-loaded, collisionless shock and it is one of the smallest of the solar system (both in absolute size and in terms of the solar wind ion gyroradii, of the same order of the curvature radius). This raises questions related to which particle acceleration and energy dissipation mechanism can take place, when its small size means dissipation timescales are too long for a stationary shock to convert the excess kinetic energy into heat. In addition, this shock coexists with ultra-low frequency (ULF) upstream waves, that are generated from the pick-up of exospheric ions.  

We use MAVEN plasma and magnetic field data to show that the fine structure of the Martian supercritical quasi-perpendicular shock (given by the typical supercritical substructures: the foot, ramp and overshoot) is in many ways comparable with that of the Terrestrial shock, which presents a substantially different solar wind – planet interaction. We observe a shock foot of the order of an upstream ion convected gyroradius, that agrees with the model of specular reflection of foot formation (Woods, 1971; Livesey et al., 1984; Gosling and Thomsen, 1985). Also, we find that the shock ramp is typically very narrow, of the order of a few electron inertial lengths. The presence of a well-defined foot and overshoot confirm the importance of dissipative effects, even in such a small bow shock boundary. 

In this work we also provide a meticulous analysis methodology that stresses the importance on the correct processing of MAVEN data, and the clarity and consistency of the criteria used in the data selection and analysis. We pay special attention to the determination of the external limit of the entry to the ion foot and the identification of the main and secondary overshoots, where the presence of the ULF waves could mean an erroneous identification of these shock features. We also attempt to assess the non-stationarity of the shock substructures, even with the limitations of a single spacecraft mission, by computing a range of local shock speeds to obtain the substructures spatial widths from the timeseries within an upper and lower value.

How to cite: Burne, S., Bertucci, C., Mazelle, C., Morales, L., Meziane, K., Espley, J., Halekas, J., Mitchell, D., and Penou, E.: Refined study of the structure of the quasiperpendicular supercritical Martian shock: new results and methodology, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-986, https://doi.org/10.5194/epsc2020-986, 2020.

We investigate the effects of the upstream solar wind magnetic field on the Martian induced magnetosphere. This is a two-spacecraft study, for which we use Mars Express (MEX) magnetic field magnitude data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument and Interplanetary Magnetic Field (IMF) measurements and solar wind density and velocity from the magnetometer (MAG) and the Solar Wind Ion Analyzer (SWIA) on board Mars Atmosphere and Volatile EvolutioN (MAVEN), from November 2014 to November 2018. Equally temporally spaced echoes appear in MARSIS' ionograms from which the electron cyclotron frequency and eventually the magnitude of the local magnetic field can be calculated. At the same time solar wind magnetic field data and solar wind parameters from MAG and SWIA respectively are utilized, providing the solar wind input to the Martian system. We make real time comparisons of the IMF and the induced magnetic field in the environment of Mars and we test the ratio B_(MEX) /B_(MAVEN)  against various parameters such as the solar wind dynamic pressure, velocity, density, Mach number as well as the Martian seasons, latitudes and heliocentric distances. Additionally, we search for disturbances in IMF which then can be traced in the induced field ultimately revealing the response time of the induced magnetosphere to the solar wind behaviour. 
MEX and MAVEN measurements combined allow us to investigate the response of the Martian induced magnetosphere to the solar wind magnetic field. Real time comparisons of the IMF and the induced field could help us understand the mechanisms controlling the structure of the Martian induced magnetosphere. 

How to cite: Stergiopoulou, K., Edberg, N., Andrews, D., and Sánchez-Cano, B.: A two-spacecraft study of Mars induced magnetosphere's response to upstream conditions, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-788, https://doi.org/10.5194/epsc2020-788, 2020.

Figure 1: MEX-MaRS X-band observations of the dayside ionosphere of Mars for (a) Day of Year (DoY) 343 (2005) and (b) DoY 215 (2014).  Combined X- and S-band (differential Doppler) observations for (c) DoY 011 (2014) and (d) DoY 006 (2006). The gray dashed line indicates the noise level, while the black dashed line marks the lowest valid altitude of the individual observation (details about the parameter derivation in [2]).

The Mars Express Radio Science experiment (MaRS) on board the Mars Express spacecraft has observed the Mars atmosphere and ionosphere since 2004. More than 900 high-resolution MaRS height profiles of the ionospheric electron density from the topside down to the ionospheric base are available.

The two dominant features of the undisturbed Martian dayside ionosphere are the main peak (M2), caused mainly by solar radiation in the Extreme Ultraviolet, and the secondary layer (M1), mostly formed by primary and secondary impact ionization of short solar X-rays < 10 nm [1]. The region below the M1 peak is highly variable and regularly contains merged excess electron density regions (Mm) in various shapes [2] (Figures 1).

More than 15 years of MaRS radio science observations are used to study the behavior of the lowest region of the Martian dayside ionosphere. Categories for the identified Mm shapes are defined and statistics of the individual Mm shape occurrences are provided. The 1-D photochemical model IonA-2 (Ionization in Atmospheres 2 [2]) is applied to investigate which of the identified Mm shapes can be reproduced by solar radiation of the quiet Sun and under solar M- and X-flare conditions.

References

  [1] Fox J. L. et al. (1996), Adv. Space Res., 17, 11, 203-218.

  [2] Peter K. (2018), PhD Dissertation, https://kups.ub.uni-koeln.de/8110/.

How to cite: Peter, K., Pätzold, M., Molina-Cuberos, G., González-Galindo, F., Witasse, O., Tellmann, S., Häusler, B., and Bird, M.: The lower dayside ionosphere of Mars in light of MEX MaRS radio science observations, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-528, https://doi.org/10.5194/epsc2020-528, 2020.

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.

How to cite: Fillingim, M., Johnson, C., Mittelholz, A., Langlais, B., Russell, C., Joy, S., Chi, P., Lillis, R., Espley, J., Smrekar, S., Banerdt, B., and Jakosky, B.: A First Comparison Between Ionospheric and Surface Level Magnetic Fields at Mars, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-999, https://doi.org/10.5194/epsc2020-999, 2020.