TP2
This session focuses on the space environments, including auroral phenomena of Mars, Venus, Pluto, Titan, Jovian moons, comets, and related comparative studies, including analogies with the ionospheres of magnetized bodies. We invite abstracts addressing remote‑sensing and in‑situ observations, modelling efforts, instrumentation, and mission concepts.
Topics may include, but are not limited to: day‑ and night‑side ionospheric variability; sources and drivers of ionization; ion‑neutral interactions; current systems; comparative ionospheric and auroral studies across bodies; and solar‑wind–ionosphere coupling, including the response of neutral and ionized regimes to transient space‑weather events. Abstracts addressing general plasma processes and atmospheric escape are also welcome.
It is widely believed that Mars had a warm and humid climate more than 4 billion years ago, as it maintained a thick atmosphere and sustained liquid water. In contrast, present-day Mars has only a thin atmosphere, and no liquid water remains on its surface. This indicates that Mars has undergone significant atmospheric escape into space and associated atmospheric evolution over the past 4.6 billion years. A key process in understanding this evolution is the escape of carbon dioxide (CO2) and carbon monoxide (CO), the dominant components of the Martian atmosphere. These gases escape not only as molecules but also as carbon (C) and oxygen (O) atoms or, particularly in the upper atmosphere, as ions through dissociative ionization. This suggests that carbon is a useful tracer of thermospheric CO2 and CO variation, as well as ionospheric variability on Mars. Sakai et al. (2024) investigated the emission mechanisms of C II 133.5 nm and found that C II emission is driven by both dissociative ionization and electron impact ionization of CO2 and CO in the lower ionosphere. Their findings suggest that C II emission may not serve as a tracer of ionospheric variability but rather as an indicator of variability in the Martian thermosphere, where CO2 and CO dominate.
In contrast, C I emission has the potential to be a more direct tracer of Martian ionospheric variability. Lo et al. (2022) demonstrated that C I 156.1 nm emission is primarily driven by electron impact below an altitude of 140 km, where the emission is most intense. This suggests that suprathermal electrons associated with the ionosphere may play a key role in determining this emission. Gérard et al. (2026) further showed that electron impacts with both CO2 and CO contribute significantly to C I 156.1 nm emission. The present study aims to elucidate the relationship between suprathermal electrons and C I 156.1 nm emission. Furthermore, an investigation is conducted into whether C I emission can serve as a diagnostic tool for ionospheric variability by estimating electron flux from the intensity of C I emission.
For this analysis, data from Solar Wind Electron Analyzer (SWEA) and Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft were used, focusing on deep dip campaigns #2 (17 – 22 April 2015), #8 (16 – 23 October 2017), and #9 (14 – 30 April 2018) as well as the aerobraking campaign (12 February – 29 March 2019). The results have indicated that C I 156 nm emission is proportional to the integrated electron flux, particularly in the energy range of 25 – 400 eV, and the CO2 density rather than to altitude. In contrast, Imaging Ultraviolet Spectrograph (IUVS) onboard MAVEN has observed C I emission brightness approximately one order of magnitude greater than that inferred from in-situ observations. Even when observations are made at the same altitude, differences in CO2 density can alter the relative contributions of multiple C I emission processes; therefore, the brightness observed by IUVS may be higher than that observed in situ. Electron impact on CO can contribute up to about 30% of the C I emission relative to that produced by electron impact on CO2. However, at altitudes where CO2 density exceeds 1010 cm-3, electron-impact C I emission remains dominant, indicating that this emission can serve as a tracer of suprathermal electrons in the Martian ionosphere.
References:
Gérard, J. C., Soret, L., Hubert, B., Lillis, R., Jain, S., & Deighan, J. (2026). Far ultraviolet carbon emissions in the Mars aurora: Brightness, intensity ratios and seasonal dependence. Icarus, 448, 116919. https://doi.org/10.1016/j.icarus.2025.116919
Lo, D. Y., Yelle, R. V., Deighan, J. I., Jain, S. K., Evans, J. S., Stevens, M. H., et al. (2022). MAVEN/IUVS observations of C I 156.1 nm and 165.7 nm dayglow: Direct detection of carbon and implications on photochemical escape. Icarus, 371, 114664. https://doi.org/10.1016/j.icarus.2021.114664
Sakai, S., Nakagawa, H., Deighan, J., Jain, S. K., Masunaga, K., Tsuchiya, F., et al. (2024). C+ 133.5 nm emission mechanisms on Mars revealed by the MAVEN observations. Ap. J., 977:226. https://doi.org/10.3847/1538-4357/ad8e35
How to cite: Sakai, S., Deighan, J., Nakagawa, H., Tsuchiya, F., Masunaga, K., Mitchell, D., Benna, M., Schneider, N., Terada, N., Jain, S., Mayyasi, M., Mazelle, C., Lillis, R., Curry, S., and Seki, K.: Electron-impact C I 156.1 nm emission as a probe of Martian ionospheric variability, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-165, https://doi.org/10.5194/epsc2026-165, 2026.
The Martian upper atmosphere exhibits strong variability driven by both external forcing from the Sun, like flares, interplanetary coronal Mass Ejection (iCME), and internal atmospheric processes [1]. Among the latter, regional and global dust storms modify the thermal structure and circulation of the lower atmosphere, with effects that can propagate upward into the thermosphere and exosphere [2]. It is important to understand how these processes alter the composition and structure of the upper atmosphere is essential for interpreting atmospheric escape and for future aeronomy investigations at Mars.
In this work, we investigate the response of the Martian thermosphere and ionosphere during the disturbed period of late March–early April 2015 using measurements from the Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard MAVEN. This interval coincided with both intense solar activity, including SEP/iCME events, and the development of a regional dust storm. To quantify the atmospheric response, quiet-time reference conditions were first established using MAVEN observations from 1–3 March 2015. Variations in neutral density profiles, scale heights, and composition were then examined for CO₂, O, N₂, and Ar in the 180–220 km altitude region.
The analysis reveals a clear thermospheric expansion in CO₂, N₂, and Ar densities during the disturbed period, while atomic oxygen exhibits a significant decrease above ~180 km. In addition, the O/CO₂ ratio decreases substantially, indicating a shift toward a more CO₂-dominated upper atmosphere. Density profiles also show signatures of wave-like structures, suggesting enhanced vertical coupling associated with dust-driven atmospheric dynamics. Dust maps constructed using Mars Climate Database simulations confirm the presence and growth of a regional dust storm during the same interval, supporting the interpretation that lower-atmosphere forcing played a major role in the observed thermospheric variability.
The ionospheric response derived from NGIMS ion measurements shows enhanced CO₂⁺ and O⁺ densities, whereas O₂⁺ remains comparatively stable. These variations appear closely linked to the changes in neutral composition and thermospheric structure. While simultaneous SEP/iCME activity may also have contributed to the observed perturbations, the results indicate that dust storm effects were likely the dominant driver of the large-scale neutral and ionospheric modifications during this period.
This study contributes to ongoing efforts to delineate the coupled influences of space weather and lower-atmospheric forcing on the Martian upper atmosphere and exosphere. The results are important in the context of the proposed M-MATISSE mission, particularly for the scientific definition of the M-INEA instrument, by helping identify the key neutral and ionized species, altitude regions, and variability signatures that future in situ investigations should target.
References
[1] Lee CO, Sánchez-Cano B, DiBraccio GA, Mayyasi M, Xu S, Chamberlin P, Davies E, Scolini C, Filwett RJ, Ramstad R, Palmerio E, Lynch BJ, Luhmann JG, Ehresmann B, Guo J, Allen RC, Vines S, Winslow R and Elliott H (2023), Heliophysics and space weather science at ∼1.5 AU: Knowledge gaps and need for space weather monitors at Mars.Front. Astron. Space Sci. 10:1064208. doi: 10.3389/fspas.2023.1064208
[2] Elrod, M. K., Bougher, S. W., Roeten, K., Sharrar, R., & Murphy, J. (2020). Structural and Compositional Changes in the Upper Atmosphere Related to the PEDE‐2018 Dust Event on Mars as Observed by MAVEN NGIMS. Geophysical Research Letters, 47, e2019GL084378. https://doi.org/10.1029/2019GL084378
How to cite: Mukundan, V., Milillo, A., Mangano, V., Leblanc, F., Felici, M., Stumpo, M., D’Amicis, R., and Benna, M.: Dust-Storm-Driven Variability in the Martian Thermosphere and Ionosphere Observed by MAVEN/NGIMS, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-492, https://doi.org/10.5194/epsc2026-492, 2026.
The martian atmosphere is sensitive to disturbances in interplanetary space due to the absence of a strong planetary magnetic field. Solar energetic particle (SEP) events comprise high-energy, electrically-charged sub-atomic particles and are produced during solar flares and coronal mass ejections. Previous work has shown that SEPs result in diffuse aurorae, disruption of radio propagation, the dispersion of atmospheric compounds, and the ionisation of atmospheric layers. In this study, we explore the relationship between SEP events and lower-atmospheric heating at Mars. Five SEP events with durations of four days or longer were identified in the years 2020-2021. Measurements from the Mars Atmosphere And Volatile EvolutioN (MAVEN) mission and the Trace Gas Orbiter (TGO) spacecraft are compared to atmospheric temperature profiles derived from the Mars Climate Database. Specifically, Mars’ lower-atmospheric temperature profiles before, during and after the SEP events are analysed. No strong evidence is found that indicates SEP events lead to the heating of Mars’ atmosphere. However, in the one case, a SEP event occurred concurrently with an expanding global dust storm. In this case, a clear heating effect is observed, but further research is required to attribute atmospheric temperature variations as a result of the global dust storms and SEP events where the two occur simultaneously.
How to cite: Williams, L., Wild, J. A., Sanchez-Cano, B., Lopez Valverde, M.-A., and Gonzalez-Galindo, F.: Do Solar Energetic Particle events impact lower-atmospheric temperatures on Mars? , Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-221, https://doi.org/10.5194/epsc2026-221, 2026.
Mars has no global intrinsic magnetic field; however, it does have strong remnant crustal magnetic fields concentrated mainly in the southern hemisphere of the planet. Whether or not these crustal magnetic fields shield Mars from radiation or allow the precipitation of high energy particles is currently an unanswered question. To help address this outstanding problem, we have analysed radar observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on Mars Express at 0.1 – 5.5 MHz and the SHAllow RADar sounder (SHARAD) on Mars Reconnaissance Orbiter (MRO) at 20 MHz, both across both the dayside and nightside of the planet.
During solar energetic particle events, high energy particles from the sun create a sporadic ionospheric layer at 60 – 90km in Mars’ ionosphere, a region not typically ionised. This leads to the attenuation of the MARSIS and SHARAD radar signals which propagate through the sporadic layer as shown in Figure 1. The extent of the radar signal attenuation is inversely proportional to the radar frequency. Since SHARAD uses a higher frequency, it is in principle more difficult to attenuate and this can help us understand the threshold of solar energetic particle fluxes and energies for shielding effects. The absence of the sporadic layer over the crustal field regions - when the sporadic layer appears elsewhere - indicates that an extra process has limited the ability of incoming solar particles to penetrate into the atmosphere. The extent of attenuation is also affected by the energy of the incoming solar particles, whether they are electrons or ions, the Martian season, column of the atmosphere, and the solar cycle.
In our study, we focus on three major events that occurred at different phases of the solar cycle, with all of them occurring on the day and nightsides. We show that the lack of attenuation of the MARSIS and SHARAD radars in the southern hemisphere of Mars may be due to localised crustal magnetic field shielding during solar energetic particle events.
By analysing where the attenuation of these two radars occurs over the planet, we have found indications that potential regional shielding may be in place over the stronger crustal magnetic fields. We have developed a catalogue of attenuated measurements during radar observations from 2006 to 2024 and found that statistically, there is a 50% greater probability of finding partial radio attenuation outside of the strong crustal field regions in the northern hemisphere, indicating a potential magnetic shielding effect. We compare three major solar energetic particle events, namely the 10 September 2017 event, the 15 February 2022 event, and the 20 May 2024 event, using analysis of radar attenuation as well as incoming particle fluxes and energies using Mars Atmosphere and Volatile Mission’s (MAVEN) Solar Energetic Particle (SEP) instrument. We have found evidence of shielding during at least the 15 February 2022 event and the 20 May 2024 event, with greater particle fluxes required to form the sporadic layer over the strong crustal field regions of the planet. This indicates a potential affect of the solar cycle in local magnetic shielding when comparing the two latest events to the 10 September 2017 event.
Figure 1: A schematic showing possible radar interactions with Mars’ ionosphere and surface. The spacecraft housing the radar is shown in grey. The purple shows the radar beam’s reflection from the main ionospheric layer. The green shows the radar beam’s path in the case of a surface reflection. The red shows the beam’s path when absorption by the sporadic layer causes attenuation and a non-reflection of the beam.
How to cite: Hanna, C., Sánchez-Cano, B., Meggi, D., Joyce, S., Contreras-Dominguez, M., Lester, M., Martindale, A., Cartacci, M., Witasse, O., Espley, J., Guo, J., Lee, C., Fowler, C., and Campbell, B.: Potential Crustal Magnetic Field Shielding Using Mars Radar Observations, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-752, https://doi.org/10.5194/epsc2026-752, 2026.
We model the interaction of non-magnetized planets with the solar wind by combining observations and a hybrid plasma solver. The model's ionospheric ion production rate is adjusted until the simulated bow shock matches the observed location. We have studied how global characteristics, such as ionospheric ion escape and bow shock location, depend on upstream solar wind conditions. At Mars using Mars Express and MAVEN observations, and at Venus using Venus Express observations. The findings can be generalized to the interactions of non-magnetized planets with stellar winds, and changes in the interactions that depend on the upstream solar wind conditions.
How to cite: Holmström, M., Wang, X.-D., Zhang, Q., and Brössner, L.: Ion Escape and Bow Shock Location at Non-Magnetized Planets, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-409, https://doi.org/10.5194/epsc2026-409, 2026.
Mars was impacted by a series of Interplanetary Coronal Mass Ejections (ICMEs) during a period of intense solar activity in May 2024. A particularly strong ICME arrived on May 17, and its impact was observed by plasma and fields instruments on the Mars Atmosphere and Volatile EvolutioN (MAVEN) and Mars Express (MEX) orbiters. At this time, MEX was well-positioned to observe the upstream solar wind, while MAVEN's orbit had fortuitously precessed to cover the deep induced magnetotail, providing an unusually clear-cut view of escaping atmospheric plasma and the effects of the ICME impact. We compare MAVEN and MEX measurements of solar wind and escaping ions before, during, and after the May 17 ICME impact to investigate how the evolution of the upstream solar wind properties affected the acceleration and resulting fluxes of escaping atmospheric ions. Our analysis of this event reveals non-linear time-dependent effects of the solar wind properties on the ion escape process.
How to cite: Ramstad, R., Hanley, K. G., Holmström, M., Halekas, J., Espley, J., Brain, D., and Curry, S.: The Evolving State of the Ion Escape Process During the May 17, 2024 ICME Impact on Mars, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1232, https://doi.org/10.5194/epsc2026-1232, 2026.
Venus’ induced magnetosphere forms through the interaction between the solar wind and the planet’s highly conductive ionosphere. The solar wind, which is frozen-in to the interplanetary magnetic field (IMF), slows down upstream of the obstacle, while it flows largely unaffected away from it. The interaction causes the IMF to drape around Venus, forming the induced magnetotail on the nightside. The magnetotail acts as the main channel for atmospheric escape, as planetary plasma is accelerated downstream by the highly bent magnetic field lines [1]. However, plasma in the magnetotail is often observed flowing Venusward, reducing the net escape to space [2]. These Venusward flows, also known as return flows, have been quantified by Venus Express plasma measurements [3]. However, the process responsible for reversing the plasma velocity and creating the return flows is yet unknown, although magnetic reconnection was proposed as a possible triggering mechanism [4].
Here, we analyse magnetic field (MAG) [5], ion (ASPERA-4/IMA), and electron (ASPERA-4/ELS) [6] data throughout the Venus Express (VEX) mission, aiming to understand the physics of return flows. We perform a statistical analysis correlating return flows with magnetotail plasma processes, including Hall magnetic field configurations, electron bursts, multiple current sheet crossings, and flux ropes. Hall magnetic fields are a consequence of ions and electrons decoupling from the magnetic field around a reconnecting X line, and are widely interpreted as a signature of collisionless reconnection [7]. Energetic and periodic electron bursts [8], multiple current sheet crossings associated with magnetic field fine structures or current sheet flapping [9], and closed magnetic loops such as flux ropes [10] were also observed in the Venus magnetotail and suggested to be a consequence of reconnection.
We find that ion return flows are observed more frequently when the Hall magnetic field configuration is measured, compared to orbits with quiet magnetotail intervals. This indicates that magnetic reconnection can drive the return flows. However, return flows are still observed in cases without Hall magnetic field structures. Correlations with the other potential magnetic reconnection signatures were also studied, but our results show that return flows occur less frequently with these plasma processes than with Hall magnetic field events.
In the presentation, we will discuss the different magnetotail plasma processes, their effect on magnetotail dynamics, and their role as possible return flow drivers.
[1] Futaana, Y., Stenberg Wieser, G., Barabash, S., & Luhmann, G. J. 2017, SSR, 212, 1453, doi: 10.1007/s11214-017-0362-8
[2] Dubinin, E., Fränz, M., Zhang, T. L., et al. 2013, JGRA, 118, 7624, doi: 10.1002/2013JA019164
[3] Persson, M., Futaana, Y., Fedorov, A., et al. 2018, GRL, 45, 10805, doi: 10.1029/2018GL079454
[4] Zhang, T. L., Baumjohann, W., Lu, Q. M., et al. 2012, Science, 336, 567, doi: 10.1126/science.1217013
[5] Zhang, T. L., Baumjohann, W., Delva, M., et al. 2006, P&SS, 54, 1336, doi: 10.1016/j.pss.2006.04.018
[6] Barabash, S., Sauvaud, J., Gunell, H., et al. 2007, PSS, 55, 1772, doi: 10.1016/j.pss.2007.01.014
[7] Halekas, J. S., Eastwood, J. P., Brain, D. A., Phan, T. D., Øieroset, M., Lin, R. P 2009, JGR, 114, A11204, doi: 10.1029/2009JA014544
[8] Dubinin, E., Fränz, M., Woch, J., et al. 2012, GRL, 39, L01104, doi: 10.1029/2011GL049883
[9] Masunaga, K., Futaana, Y., Persson, M., et al. 2019, Icarus, 321, 379, doi: 10.1016/j.icarus.2018.11.017
[10] Hara, T., Huang, Z., Mitchell, D. L., et al. 2022, JGRA, 127, e2021JA029867, doi: 10.1029/2021JA029867
How to cite: Rollero, U., Futaana, Y., and Wang, X.-D.: Magnetotail plasma dynamics and return flow at Venus , Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-439, https://doi.org/10.5194/epsc2026-439, 2026.
Callisto possesses a tenuous atmosphere and ionosphere that play an important role in its interaction with the Jovian magnetospheric plasma. However, the structure, asymmetry, and vertical distribution of the atmosphere remain poorly constrained. These uncertainties may significantly affect plasma interaction processes and the interpretation of magnetic induction signatures, which are important for investigating the subsurface properties of Callisto and for future observations by the JUICE mission. In this work, we systematically investigate how different atmospheric structures and asymmetries influence the plasma environment around Callisto. Our preliminary results suggest that atmospheric properties can substantially modify the amplitudes and spatial distributions of magnetic perturbations associated with the interaction. While different atmospheric scale heights generally produce similar large-scale trends and dominant characteristics, noticeable differences appear in the amplitudes of the perturbation signals and in the extent of the interaction region. These findings highlight the importance of realistic atmospheric parameterizations in future studies of Callisto’s plasma environment and magnetic induction processes.
How to cite: Long, M., Saur, J., and Duling, S.: Effects of Atmospheric Structure on the Plasma Interaction at Callisto, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-354, https://doi.org/10.5194/epsc2026-354, 2026.
Electron density is one of the most important measurable parameters in space plasma. The electron density provides important information about the local plasma properties at Titan, constraining the plasma wave propagation, possible photochemical reactions and effectiveness of the energy-momentum processes. Therefore, the accurate measurement is critical for the understanding of the general structure and dynamics of Titan’s plasma environment. Cassini-Huygens performed 126 close flybys of Titan, performing both active and passive measurements of the electron density. In this study, we focus on the Radio and Plasma Wave Science (RPWS) instruments, such as the Langmuir probe and electrical antennas, and the comparison of the derived electron density values in Titan’s ionosphere. We show that the estimates from the electrical antennas (using the identification of the upper-hybrid resonance line) systematically overestimate the electron density in the lower ionosphere of Titan. We propose that the main cause is the inability to identify precisely the upper-hybrid resonance line. Moreover, the upper-hybrid line splits into the upper- and lower-band, with the lower-band identified as the upper-hybrid wave and the upper of unknown origin. After the electron density correction, we find that the overestimation comes from the wrong identification of the upper-hybrid line, and show that the corrected electron densities are overestimated, but by the LP. We discuss possible reasons for the discrepancy and recommendations on how to implement corrections to the analysis.
How to cite: Kim, K., Wahlund, J.-E., Edberg, N. J. T., Wu, S., and Kurth, W.: Comparison of the electron density measurements in Titan’s ionosphere, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-856, https://doi.org/10.5194/epsc2026-856, 2026.
Comets are strong sources of energetic neutral atoms(ENAs)originating from solar wind charge exchange within their extended neutral gas environments. Moreover, acceleration processes in the vicinity of comets produce energetic particles with energies significantly higher than the solar wind, in the range of tens to hundreds of keV. Charge exchange of these particles generates high-energy ENAs that propagate like photons, unaffected by electromagnetic fields and only negligibly influenced by gravity. Observations of cometary high-energy ENAs reveal acceleration processes at the comet, characterize its neutral environment, and can effectively deliver direct samples of cometary material to the observation point. The JUICE spacecraft, carrying the high-energy ENA imager JENI (Jovian Energetic Neutrals and Ions), covering the energy range 1–110 keV (ENAs), attempted for the first time to detect ENAs from a comet in this energy range. The target was 3I/Atlas, an interstellar object, making this attempt particularly valuable. On 4 November, 3I/Atlas was at a minimum distance of 66 million km from the JUICE spacecraft. The comet was observed from 8 to 19 November, when the observation geometry became compatible with spacecraft constraints. During this period, the spacecraft–comet distance ranged from approximately 80 to 150 million km. For a reported outgassing rate of (1–2) × 1029 s-1, the expected ENA intensity is estimated to be 10-4 to 10-3 (eV cm² s sr)-1, which remains above the JENI detection limit of 10-5 (eV cm² s sr)-1 against the ultraviolet background. The 10-day observation period enabled extremely long integration times. The data from this period were downlinked in February and being analyzed. We report the results of these observations, which will either constitute the first direct detection of particles from an interstellar object or provide an upper limit for high-energy ENA intensity from a comet.
How to cite: Barabash, S., Clark, G., Brand, P., Kollmann, P., Mitchell, D., Regoli, L., Gkioulidou, M., Allegrini, F., Wurz, P., Krupp, N., Roussos, E., Turner, D., and Paty, C.: ESA’s JUICE: first-ever attempt to observe energetic neutral atoms from an interstellar object, the 3I/Atlas comet, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1226, https://doi.org/10.5194/epsc2026-1226, 2026.
How to cite: Steinwand, V., Chittenden, J., Chaturvedi, N., Beth, A., and Galand, M.: A new multifluid cometary plasma model, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1197, https://doi.org/10.5194/epsc2026-1197, 2026.
Electromagnetic waves at the local proton cyclotron frequency are frequently observed upstream from the Martian bow shock. They are excited by unstable velocity distributions of newborn protons continuously produced locally by ionization of exospheric hydrogen atoms (pickup protons). The analysis of MAVEN magnetic field data demonstrates for the first time that the amplitude of these waves undergo a sharp change when crossing the electron foreshock boundary. Moreover, a decrease of the amplitude with the increasing distance from the shock along the ambient average magnetic field is observed inside the foreshock. Both signatures are correlated with the variations of the energetic electron fluxes. These two properties connecting the wave growth to electron physics raise an issue since the waves are excited purely through an ion-ion instability. We propose that the extra free energy necessary to increase the wave amplitude is due to additional ionization of hydrogen atoms by electron impact ionization inside the foreshock. These results imply that extreme caution is needed when directly deriving the exospheric density at Mars and other similar environments from the local pickup ion wave amplitude, especially in the foreshock region.
How to cite: Mazelle, C., Meziane, K., Simon-Wedlund, C., Bertucci, C., Zhang, C., Romanelli, N., Fruchtman, J., Hamza, A., Halekas, J. S., Espley, J. R., Mitchell, D. L., and Curry, S.: Effect of Foreshock Electron Impact Ionization on the Amplitude of Pickup Proton Driven Waves: Implication for Exosphere Density Estimates, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1042, https://doi.org/10.5194/epsc2026-1042, 2026.
In the terrestrial foreshock, sunward propagating ion beam of several keV collimated along the interplanetary field lines (Field-Aligned Beams)
are usually observed within a region upstream from the quasi-perpendicular shock. Numerous observations indicate that these beams are not seen along IMF lines that make a angle larger than 70o with the local shock normal, thereby marking
the edge of the ion foreshock. The ion foreshock boundary reflects the maximum level of energization that solar wind ions can reach via coherent interaction with a planetary shock. In the present study, the Martian ion foreshock boundary
is investigated for the first time using MAVEN particle and magnetic field data. We found that no FAB is observed for a shock-θBn larger than 50o-55o. Our results indicate that the Martian ion foreshock boundary is located downstream of its terrestrial counterpart. This finding is in good agreement with
a recent report showing that FABs observed in the Martian foreshock have noticeably lower speeds than those observed at Earth.
How to cite: Meziane, K., Mazelle, C., Hamza, A., Simon-Wedlund, C., Bertucci, C., Halekas, J., Mitchell, D., Espley, J., and Curry, S.: An Ion Foreshock Boundary Upstream of the Martian Bow Shock, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1074, https://doi.org/10.5194/epsc2026-1074, 2026.
KHI can grow into finite-amplitude Kelvin–Helmholtz waves (KHWs), which may subsequently roll-up into large-scale vortices (KHVs). These vortices can twist magnetic field lines and trigger vortex-induced tearing mode instability (TMI). In the context of planetary magnetospheric dynamics, such instabilities are fundamental because they (i) drive substantial mass, energy, and momentum transport from the MSH into the MSP; (ii) generate ultra-low-frequency magnetospheric waves; and (iii) drive field-aligned currents (FACs), that are the major means of coupling the magnetosphere to the ionosphere, contributing to the auroral activity.
In this work, we analyze two prominent SWE events that occurred in January and November 2025, during which the Sun produced some of the strongest flares of Solar Cycle 25, associated with Earth-directed coronal mass ejections (CMEs).
In the January event case, we combine in-situ magnetospheric observations from MMS with ionospheric measurements from Swarm in order to assess the generation of FACs (Figure 1) due to the twisting and shearing of magnetic flux tubes by KHVs. To confirm the development of the vortices and the correpsonding currents firstly we use a magneto-hydrodynamic (MHD) model (Figure 2), MIM (Biasiotti et al. 2024, Ivanovski et al. 2011), and then we examine ionospheric irregularities using data from a network of ground-based observatories, including GNSS receivers providing total electron content (TEC) and scintillation measurements, as well as ground magnetometer observations of the horizontal equivalent ionospheric currents (EIC) and the vertical spherical elementary current (SEC).
Whereas, for the November 2025 SWE, we investigate the development of KHI following the arrival of a interplanetary CME combining in-situ observations from THEMIS (Figure 3) with magneto-hydrodynamic (MHD) simulations, in order to assess wheter the periodic variations of the IMF Bz expose the magnetospheric system to successive intervals of magnetic flux and mass loading, which can enhance the ring current (and hence the strength of the geomgnetic storm) through plasma energization driven by tail reconnection, as proposed by Nykyri (2024). More specifically, intervals of southward IMF enable magnetic flux entry via dayside reconnection, while subsequent northward IMF can facilitate plasma transport from the flanks into the plasma sheet due to KHI.
Figure 1. Geographic maps of J acquired by the Swarm constellation during orbits 19 and 20 (from T0 at 16:55 UT) in the Northern hemisphere. The red and yellow points mark the ionospheric region corresponding to that identified by the TA15 model, and the longitude of the subsolar point, respectively.
Figure 2. Temporal evolution of plasma density (upper panel) and jz (lower panel), from 1 to 15 s. Kelvin-Helmholtz vortices are formed rapidly at 5 s. As the KHVs develop, twin-vortex structures, i.e. oppositely rotating current cells, are generated.
Figure 3. Overview of ACE real-time solar wind data and THEMIS observations. SYM-H index from OMNI (a), ACE data of magnetic field magnitude and components (b), ion density (c), ion bulk velocity (d), and ion temperature (e). Position of THA and THD in respect to the magnetopause (f). THA/THD observations of ion energy spectrogram (g/m), ion velocity (h/n), ion density and temperature (i/o), magnetic field components and magnitude (j/p), the mangetic field normal direction estimated with MVAE method (k/q) and the total pressure of the plasma (l/r) during the interval 14:05-15:05 UT on 13 November 2025. The coloured bars at the top show a classification of the THEMIS data based on (Grimmich et al., 2023), indicating whether it is more likely to be magnetosheath data (orange) or magnetosphere data (blue).
Acknowledgment:
This research has been carried out within the framework of the Space It Up project funded by the Italian Space Agency, ASI, and the Ministry of University and Research, MUR, under contract n. 2024-5-E.0 - CUP n. I53D24000060005.
References:
Biasiotti L, Ivanovski S, Calderone L, et al., 2024, Evidence of Kelvin-Helmholtz and tearing mode instabilities at the magnetopause during space weather events, Front. Astron. Space Sci., 11:1395775, doi: 10.3389/fspas.2024.1395775
Grimmich, N., Plaschke, F., Archer, M. O., et al., 2023, Study of extreme magnetopause distortions under varying solar wind conditions, Journal of Geophysical Research: Space Physics, 128, e2023JA031603, https://doi.org/10.1029/2023JA031603
Ivanovski, S., Kartalev, M., Dobreva, P., et al., 2011, Coupled Kelvin-Helmoltz and tearing mode instabilities in the magnetopause layer, JTAM, 41(3), 31–42.
Nykyri, K.,2024, Giant Kelvin-Helmholtz (KH) waves at the boundary layer of the coronal mass ejections (CMEs) responsible for the largest geomagnetic storm in 20 years, Geophysical Research Letters, 51, e2024GL110477, https://doi.org/10.1029/2024GL110477
How to cite: Biasiotti, L., Ivanovski, S., Alfonsi, L., De Michelis, P., Dogo, F., Giannattasio, F., Grimmich, N., Nykyri, K., and Simonetti, P.: Exploring the development of Kelvin-Helmholtz instability at the Earth's magnetospheres during intense space weather events, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-477, https://doi.org/10.5194/epsc2026-477, 2026.
Fig. 1:. 4 VEX VeRa nightside electron density profiles. nS are the smoothed electron density profiles. 6ˑσS indicates the conservative threshold for ionospheric signature detection. hval is the lowest valid altitude of the observation. nu/hu and nL/hL are the identified upper and lower peak electron density/altitude, respectively.
Earth occultation radio science observations provide a powerful tool to probe the structure of planetary ionospheres. During its mission at Venus from 2006 and 2014, the Venus Express (VEX) spacecraft conducted more than 900 ingress and egress occultations with the Venus Radio Science experiment (VeRa), providing high resolution electron density profiles of the Venus dayside, terminator, and nightside ionosphere. In this study, 335 low noise level VeRa observations are analyzed to characterize the temporal and spatial variability of ionospheric structures at solar zenith angles (SZA) ranging from the terminator to the deep nightside.
On the planetary dayside, the altitude of the main ionospheric peak (V2) remains remarkably stable, with an average altitude of ~141 km and only minor variability. A modest increase in peak altitude is observed near the terminator, in good agreement with earlier results from the Pioneer Venus Orbiter radio science (ORO) experiment.
For SZAs > 90°, the ionosphere exhibits increased temporal and spatial variability. A valid ionospheric signature is detected in 97% of the lit nightside observations - where the ionosphere remains directly illuminated – and in 87% of observations on the deep nightside. Two distinct ionospheric regions are frequently identified on the planetary nightside: an upper peak and a lower peak separated by a significant reduction in electron density, indicating different formation mechanisms (Figure 1). Upper peaks occur on both the lit and deep nightside. In contrast, lower peaks are detected almost exclusively on the deep nightside, effectively ruling out direct solar EUV ionization as their primary source. Although lower peaks are observed under both low and high solar activity conditions, their occurrence rate increases with solar activity, suggesting an indirect solar-driven contribution to their formation.
Results show that the Venus nightside ionosphere is a persistent yet highly variable feature throughout the Venus Express mission time. A combined analysis of VEX VeRa electron density profiles and VEX ASPERA-4 plasma measurements will further constrain the origin and relative contributions of the processes responsible for the two distinct nightside ionospheric features.
How to cite: Peter, K., Pätzold, M., Tellmann, S., Oschlisniok, J., and Häusler, B.: The terminator and nightside ionosphere of Venus as seen by Venus Express VeRa radio science, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-208, https://doi.org/10.5194/epsc2026-208, 2026.
We present the observations of the solar wind flow into the Martian wake using the measurements by Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. It is shown that the magnetospheric boundary at the nightside is not a perfect and the solar wind protons penetrate into the tail region filled by the ionospheric plasma streaming in the antisunward direction. A more strong penetration in the E+ hemisphere results to a shift of the magnetospheric cavity to the E- hemisphere. Close to Mars, at altitudes less ~2000 km the sunward flows of the solar wind protons dominate. The sunward flows are also observed at larger distances in the ion trail filled by the low-energy ionospheric plasma. The results are compared with the hybrid simulations of the solar wind interaction with Mars. Mechanisms of a such behavior are discussed.
How to cite: Dubinin, E., Fraenz, M., Modolo, R., Paetzold, M., Tellmann, S., McFadden, J., and DiBraccio, G.: Solar wind flow into the Martian wake, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-212, https://doi.org/10.5194/epsc2026-212, 2026.
Fig. 1:. 7 MaRS terminator/nightside electron density profiles observed between August and September 2005. All profiles have an offset of 3·1010 m−3 to the neighbouring profiles. The vertical gray line indicates zero electron density for each profile. The red dot indicates the identified peak electron density, and the vertical red line indicates the lowest valid altitude of the profile.
The Mars Express (MEX) spacecraft has been orbiting Mars since December 2003. Its MaRS (Mars Radio Science) experiment uses spacecraft-Earth radio occultations to provide information about the ionospheric electron density and the pressure, density and temperature of the lower neutral atmosphere.
In this study, the variability of the Martian ionosphere (Figure 1) for solar zenith angles (SZAs) > 90° is investigated using Mars Express MaRS Earth occultation measurements acquired between 2004 and 2021. A total of 587 high-quality MaRS profiles is analyzed, supported by solar flux proxies derived from MAVEN LPW-EUVM observations, heliocentric distance, and model-derived crustal magnetic field information. The selected dataset covers SZAs up to 125°.
A substantial ionosphere is identified in 96% of the lit nightside observations, indicating that direct ionization by solar irradiation remains sufficient to sustain an ionosphere in this region under all observed levels of solar irradiance at Mars. In the deep nightside region, 68% of the observations still contain a detectable ionospheric signature. A clear correlation is observed between the occurrence of ionospheric signatures and solar irradiation flux.
The altitude of the upper ionospheric peak on the lit nightside increases up to SZAs of ~100°, showing a clear correlation with enhanced solar irradiation and atmospheric dust loading. Peak electron densities and total electron content on the deep nightside are small compared to those on the lit nightside, apart from isolated profiles likely associated with intense solar events (profile 2 in Figure 1).
These results highlight the complex and variable nature of the Martian terminator and nightside ionosphere and emphasize the importance of future radio science investigations of the deep nightside. Upcoming missions such as the proposed ESA M-MATISSE mission would provide critical new constraints on the structure and dynamics of the deep nightside ionosphere of Mars.
How to cite: Peter, K., Pätzold, M., Thiemann, E., and Tellmann, S.: The terminator and nightside ionosphere of Mars as seen by Mars Express MaRS radio science, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-213, https://doi.org/10.5194/epsc2026-213, 2026.
The meteorology and climatology of the Martian atmosphere are significantly influenced by dust activity, particularly during southern spring and summer when dust content increases. This study investigates the inter-annual variability of the Martian ionosphere. Using radio occultation data from the Mars Express Radio Science experiment (MaRS) and the MAVEN Radio Occultation Science Experiment (ROSE), vertical atmospheric profiles are generated to analyse electron densities and the underlying neutral atmospheric temperatures.
Data processing is performed with the "radiocc" code developed at the Royal Observatory of Belgium, which converts Doppler residual data into vertical profiles for both the ionosphere and neutral atmosphere. This research provides a comprehensive comparison of ionospheric data across multiple Mars Years. Key electron density parameters are derived from occultation profiles to assess the influence of dust and solar activity on the Martian Ionosphere. In addition, profile anomalies are identified as a function of location and time.
How to cite: Krishnan, A., Karatekin, O., and Witasse, O.: Martian Ionospheric Variability from Mars Express and MAVEN Radio Occultations, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1004, https://doi.org/10.5194/epsc2026-1004, 2026.
In situ measurements from the dual Langmuir Probe (LAP) and Mutual Impedance Probe (MIP) onboard the Rosetta Plasma Consortium have shown that the electron environment in the coma of comet 67P/Churyumov-Gerasimenko is typically characterized by a pronounced bimodality, consisting of a cold component with energies below approximately 0.1 eV and a warmer component centered around 5 eV. This dual structure has often been interpreted using electron-neutral collisionopause concepts, which separate electron populations based on a prescribed spatial transition. While useful for qualitative interpretation, such approaches do not explicitly resolve the underlying electron energy distribution. By assuming that electrons and ions created simultaneously experience similar time-averaged neutral density fields it becomes possible to assess electron energy distributions semi-analytically via a continuous electron energy degradation model, grounded in laboratory work for electrons in water vapor. Preliminary results show that such a model reasonably well reproduces observed fractions of cold versus warm electrons in the coma of 67P during March 2016.
How to cite: Vigren, E. and Eriksson, A.: Collisional electron cooling in the coma of comet 67P, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1154, https://doi.org/10.5194/epsc2026-1154, 2026.
