Following its launch, BepiColombo has already performed three flybys at Mercury. The next three flybys at Mercury are time wise very close together and are planned with about four months starting in September 2024. About 10 months after these flybys the orbit insertion preparation will start. When in orbit, BepiColombo with its state of the art and very comprehensive payload will perform measurements to increase our knowledge on the fundamental questions about Mercury’s evolution, composition, interior, magnetosphere, and exosphere.
Although the two BepiColombo spacecraft are in a stacked configuration during the cruise and only some of the instruments can perform scientific observations, the mission produces already some very valuable results. As an example, Mercury’s southern inner magnetosphere, a so far unexplored region, has been observed by the BepiColombo ion and fields instruments during the pass.  Data taken during the Mercury's flybys revealed a magnetosphere populated by diverse populations and confirmed a really dynamic regime. 
BepiColombo is a joint mission between the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA) for comprehensive exploration of planet Mercury. BepiColombo, has been launched on 20 October 2018 from the European spaceport Kourou in French Guyana and it is currently on a seven-year-long cruise to Mercury. BepiColombo consists of two orbiters, the Mercury Planetary Orbiter (MPO) and the Mercury Magnetospheric Orbiter (Mio). In late 2025/early 2026 these orbiters will be put in orbit around the innermost planet of our Solar System. 
During the talk a status of the mission and results from science operations during cruise will be presented.

How to cite: Benkhoff, J. and Murakami, G.: BepiColombo Mission Update, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10851, https://doi.org/10.5194/egusphere-egu24-10851, 2024.

The ESA-JAXA joint mission BepiColombo is now on the track to Mercury. After the successful launch of the two spacecraft for BepiColombo, Mio (Mercury Magnetospheric Orbiter: MMO) and Mercury Planetary Orbiter (MPO), commissioning operations of the spacecraft and their science payloads were completed. BepiColombo will arrive at Mercury in the end of 2025, and it has 7-years cruise with the heliocentric distance range of 0.3-1.2 AU. The long cruise phase also includes 9 planetary flybys: once at the Earth, twice at Venus, and 6 times at Mercury. Even before arrival, we already obtained fruitful science data from Mercury during three Mercury flybys completed on 1 October 2021, 23 June 2022, and 19 June 2023. We performed science observations with almost all the instruments onboard Mio and successfully obtained comprehensive data of Mercury’s magnetosphere such as magnetic fields, plasma particles, and waves. Here we present the updated status of BepiColombo/Mio, initial results of the science observations during the Mercury flybys, and the upcoming observation plans.

How to cite: Murakami, G. and Benkhoff, J.: Updated status of BepiColombo and initial reports on Mercury flyby observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15387, https://doi.org/10.5194/egusphere-egu24-15387, 2024.

Tolstoj quadrangle is located in the equatorial area of Mercury, between 22.5°N and 22.5°S of latitude and 144° and 216°E of latitude. In this work we present the geological map (1:3M scale) performed on the quadrangle. The main basemap used for the mapping is the MDIS (Mercury Dual Imaging System) 166 m/pixel BDR (map-projected Basemap reduced Data Record) monochrome mosaic compiled using NAC (Narrow Angle Camera) and WAC (Wide Angle Camera) 750 nm-images. Moreover, to distinguish spectral characteristics and topography of the surface, MDIS global color mosaics [Denevi et al., 2016)] and the MDIS global DEM [Becker et al., 2009), have been taken into account. Then, the quadrangle has been mapped using ArcGIS at an average scale of 1:400k for a final out-put of 1:3M. The mapping highlights as Caloris basin related features dominate the geology of H08. Indeed, the southern half of the basin is located in the upper left corner of quadrangle. Inside and outside the basin extended smooth plains were emplaced and they represent the most extended volcanic deposits in the quadrangle. Also structural framework is mainly linked with the basin with radial and concentric grabens located in its floor and wrinkle ridges widespread both on the interior and exterior Caloris smooth plains. Further, lobate scarps have been detected in the quadrangle: they are located outside the Caloris basin but they are absent within its floor. These thrusts show a preferential orientation in the smooth plains located outside the basin whereas they are more randomly oriented in the intercrater plains. Besides smooth plains, products of effusive volcanism, features related to explosive volcanism have also been frequently detected. Interestingly, several volcanic vents have been identified in the inner Caloris smooth plains, aligned with the rim of Caloris basin, suggesting a correlation between these two features. However, vents are not clustered only inside Caloris basin, but other crater floors are affected by this type of features. The vents are surrounded by extended pyroclastic deposits appearing in bright yellow in MDIS enhanced global color mosaics. Finally, hollow fields have also been mapped, although they are not very frequent. Some of them are associated to the pyroclastic deposits located along Caloris rim, the others are detected within floors or peaks of a few craters in the intercrater plains.

The geological map will be integrated into the global 1:3M geological map of Mercury (Galluzzi et al., 2021), which is being prepared in support to ESA/JAXA (European Space Agency, Japan Aerospace Agency) BepiColombo mission.

Acknowledgements:  We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0 and from the GMAP, Europlanet RI 20-24 grant n.: 871149-GMAP

References:

Becker K. J., et al. AGU, Fall Meeting, ab-stract#P21A-1189, 2009

Denevi et al.:LPS XLVII. Abstract#1264, 2016

Galluzzi V. et al.:. Planetary Geologic Mappers 2021, LPI #2610, 2021

How to cite: Giacomini, L., Guzzetta, L., Galluzzi, V., Ferranti, L., and Palumbo, P.: Geological map of Tolstoj quadrangle (H08) of Mercury, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6003, https://doi.org/10.5194/egusphere-egu24-6003, 2024.

Geological cartography and structural analysis are essential for understanding Mercury’s geological history and tectonic processes. This work focuses on the geological and structural analysis of the Michelangelo quadrangle (H12), located at latitudes 22.5°S-65°S and longitudes 180°E-270°E. We present the first geological map of H12 at 1:3,000,000 scale, based on the photointerpretation of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Mercury Dual Imaging System (MDIS) imagery. The present study is a contribution to the 1:3M geological map series, planned to identify targets to be observed at high resolution during the ESA-JAXA BepiColombo mission [1]. 

We mapped tectonic structures and geological contacts using the MDIS derived basemaps, characterized by an average resolution of 166 m/pixel. Linear features are subdivided into large craters (crater rim diameter > 20 km), small craters (5 km < crater rim diameter < 20 km), subdued or buried craters, certain or uncertain thrusts, certain or uncertain faults, wrinkle ridges and irregular pits. Geological contacts, mapped as certain or approximate, delimit the geological units grouped into three classes of crater materials (c1-c3) based on degradation degree, and plains (smooth, intermediate and intercrater plains).

Michelangelo appears as a densely cratered quadrangle dominated by degraded crater materials (c2) and intermediate plains. We identified two main regional thrust system trending NW-SE and NE-SW. We found that many lobate scarps developed at the edges of ancient, large impact basins. Clear examples of such tectonic structures in the Michelangelo quadrangle are provided by the Beethoven basin (20.8°S–236.1°E) or by the Vincente-Yakovlev basin (52.6°S–197.9°E). We propose a thick-skinned tectonic model according to which the lobate scarps were formed after positive reactivation of previous impact-related normal faults, due to the contractional tectonic regime deriving from the global contraction. Evidence of thick-skinned tectonics on Mercury are provided by the presence of fault systems exceeding the basin rim, and by the estimated rooting depth of thrusts bordering large basins (e.g., Discovery Rupes, Soya Rupes).

Following [2], we found that the NW-SE system largely borders the southwestern edge of the HMR. We also show that the volcanic vents on Mercury are often associated with impact craters and/or lobate scarps (e.g., [3,4]), which can be considered as possible preferential areas for magma uprising.

Acknowledgements: We gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0.

References:

[1] Galluzzi, V. et al. (2021). LPI Contrib., 2610.

[2] Galluzzi, V. et al. (2019). J. Geophys. Res., 124(10), 2543-2562.

[3] Thomas, R. J. et al., (2014). J. Geophys. Res., 119, 2239-2254.

[4] Jozwiak, L. M. et al., (2018). Icarus, 302, 191-212.

How to cite: Buoninfante, S., Galluzzi, V., Ferranti, L., Milano, M., and Palumbo, P.: Geology and tectonic structures of the Michelangelo (H12) quadrangle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4401, https://doi.org/10.5194/egusphere-egu24-4401, 2024.

The results from planetary investigation in the last years strongly point out that the integration of compositional information with the morphology, stratigraphy and tectonics permits to produce a more comprehensive geological approach, obtaining geological maps instead of purely morpho-stratigraphic maps. In this view, firstly PLANMAP project, and then GMAP (within EUROPLANET-RI 20-24), have given indications on different approaches to follow for such integration.
Investigating the surface of Mercury is an important task of the Bepicolombo mission. To be prepared for this task we are investigating the data obtained by past MESSENGER mission in order to understand which geological features and/or region of Mercury should hide key information.
In this work we investigate the Kuiper crater (62 kilometer in diameter) which overlies the northern rim of the larger crater Murasaki. The Kuiper crater is one of the highest albedo features on the surface of Mercury with an important ray system, indicative of  its young age. From this point of view Kuiper can be considered an important feature on hermean surface history, such as to give the name at the last period of Mercury timeline (the Kuiperian age). However, on the other side,its relatively young age does not permit it to investigate the local geology by using the global basemaps, since the albedo is saturating within the crater, making difficult to understand the variegation on it and on the proximal and distal ejecta. Whereas considering the color variegation from the different filters of the WAC camera onboard MESSENGER, at relatively high spatial resolution (385 m/px), we clearly highlighted how several peculiar geological features arise. These regions have been later investigated by ad-hoc mosaics considering the highest resolution images available (~ 120 m/pixel) from the NAC camera onboard MESSENGER.
The extension of the ejecta could be improved and differentiated from reflectance properties of the crater floor, showing an asymmetry towards S-SE. Moreover, the crater wall seems to reveal the possible impact direction. Evidence of pyroclastic-like material, from spectral reflectance properties, are present on the N-E wall, whereas from north to west the terraced wall seems to show the presence of re-melted material. Interestingly, two different hollows-like terrain are present on both the inner peaks and on the southern wall, indicating that hollows could be emplaced on different bedrock terrains. In addition, the spectral indication shows a clear distinction from Kuiper material with respect to the Murasaki terrains.
We want to acknowledge the GMAP, Europlanet RI 20-24 grant n.: 871149-GMAP and the Bepicolombo (SIMBIO-SYS) project, ASI-INAF agreement n.: 2017-47-H.0

How to cite: Carli, C., Giacomini, L., Massironi, M., Zambon, F., Galiano, A., Capaccioni, F., and Palumbo, P.: Geological mapping of Kuiper Crater: a break within Mercury crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6397, https://doi.org/10.5194/egusphere-egu24-6397, 2024.

A planet’s orbital eccentricity can experience major changes over time as a result of planetary secular perturbations. Mercury's proximity to the Sun, its unique 3:2 spin-orbit resonance, and its high orbital eccentricity makes it an intriguing subject for investigating tidal forces and their resulting stresses. Throughout its history, Mercury may have experienced a state of further heightened eccentricity, potentially leading to tidal forces significant enough to modify the planet's surface. In the study presented here, we explore the tidal potential currently influencing Mercury and examine possible historical values of eccentricity to estimate past stress values. Employing a four-layer crustal model, we calculate Love numbers that reflect Mercury's internal physical properties and compute global tidal potential, surface stresses, and radial tidal displacement with respect to location and position in orbit. A suggested past orbital eccentricity of e = 0.41 could produce estimated maximum principal surface stresses of ~ +/-70 kPa which are comparable to current diurnal tidal principal stress values for Europa and Enceladus (~ +/-85 kPa). At present, Mercury experiences tidal stress values of up to ~ +/-15 kPa with a tidal bulge that can radially displace the surface by a mean of ~ 2.3 m. As tidal stresses could have been significantly higher in the past, we can hypothesize that Mercury might have experienced surface alterations induced by its orbital dynamics. On the other hand, the present-day surface of the planet has not retained evidence of any tidal stress modifications, suggesting that these characteristics, if present, would have been likely covered by the volcanic activity that persisted up to 3 billion years ago. Sophisticated instruments like the BepiColombo Laser Altimeter (BELA), to be inserted into orbit around Mercury in early 2026 onboard the European Space Agency’s BepiColombo mission, promise to provide unprecedented data and will be instrumental in precisely measuring Mercury's global topography, contributing to a more accurate understanding of the planet's surface variations. This, in turn, will aid in refining our calculations and representations of Mercury's internal structure and its evolution.

How to cite: Burkhard, L. and Thomas, N.: Insights into Mercury’s tidal stresses: Linking present and past potentials, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7623, https://doi.org/10.5194/egusphere-egu24-7623, 2024.

The BepiColombo spacecraft, designed by ESA/JAXA, is currently in its cruise phase towards Mercury. The Mercury Orbiter Radio-science Experiment (MORE), one of the scientific investigations of the mission, will exploit a multi-frequency microwave tracking system with an advanced Ka-band transponder to fulfill scientific goals in Mercury’s geodesy and fundamental physics. Thanks to the precise measurements enabled by the state-of-the-art radio tracking system, MORE is expected to provide new insights on the planet and its interior, expanding and improving the results of the MESSENGER mission. In this work, we assess the performance of the geodesy investigation conducted by MORE, focusing on the orbital phase, starting in early 2026. In particular, this study evaluates how BepiColombo's refined gravity data can reduce the uncertainty in the estimate of the Love Number k₂, rotational state and crustal thickness of Mercury.  We report the results of the numerical simulation based on the up-to-date mission scenario, which consists of a two-year orbital phase. We simulate synthetic radio observables and estimate the model parameters through a precise analysis of the spacecraft orbital motion. We include different sources of mismodelling to reproduce a perturbed dynamical state of the probe, such as errors in the thermo-optical coefficients of the spacecraft, wheel off-loading maneuvers with unbalanced ΔVs and random fluctuations of solar irradiance, which cannot be modelled or measured by the onboard accelerometer. We use the covariance matrix coming from this analysis to perform a Monte Carlo simulation to obtain a set of gravity fields statistically compatible with a reference field (HgM009, derived from a recent reanalysis of the MESSENGER dataset). By combining these gravity fields with available topographic data, we produce a distribution of Mercury’s crustal thickness maps, from which we infer the corresponding estimation uncertainty. We compare the expected accuracies of the BepiColombo gravity experiment with the current state of knowledge. We show that MORE shall fulfill its scientific goals by improving the estimate of the planet’s gravity field, tidal response and rotational state. Our findings demonstrate how the estimate of Mercury’s crustal thickness benefits from BepiColombo’s high precision gravity measurements. The uncertainties derived from our simulation show that MORE will provide a reliable and high resolution basis for associating gravity anomalies with geological surface features on Mercury, such as impact craters, rift zones, and lobate scarps.

How to cite: Zurria, A., di Stefano, I., Cappuccio, P., De Filippis, U., and Iess, L.: Expected performance of the MORE geodesy experiment during the orbital phase of BepiColombo, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18499, https://doi.org/10.5194/egusphere-egu24-18499, 2024.

We will present the design and establishment of a cutting-edge molecular beam facility at Southwest Research Institute (SwRI). The primary focus of this facility is to support the operations of Strofio, the neutral mass spectrometer and payload of the BepiColombo mission. Testing of this instrument requires a molecular beam with an average speed of 3 km/s. Beyond serving the immediate needs of Strofio, our vision extends to collaborative efforts with other organizations in the development of future instrumentation. We look forward to fostering partnerships that will collectively advance the capabilities of in-situ particle instruments and contribute to the broader scientific community.

How to cite: Schroeder, J., Livi, S., Patrick, E., and Turner, J.: Strofio Operations: A New Molecular Beam Facility, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20823, https://doi.org/10.5194/egusphere-egu24-20823, 2024.

Mercury’s exospheric atoms are mainly ejected from the surface through several processes such as thermal input, UV irradiation, solar wind particle sputtering, and micro-meteoroid impact. Observations by the MESSENGER spacecraft have shown that Mercury magnesium (Mg) exosphere is related to its surface abundance. Additionally, Mg is an interesting species as its surface abundance reflects the non-uniformity of magma compositions. However, spatial distribution (especially in the latitude direction) and seasonal variability of Mg exosphere is not well understood due to its dark brightness and the geometry of observations.

BepiColombo, the Mercury orbiting mission led by ESA and JAXA, is on its way to the planet. The 2nd and 3rd Mercury swing-bys were conducted on 22/06/2022 and 19/06/2023 (UTC), respectively, and many instruments observed the Mercury environments then. In this study, we analyzed Mg exosphere data from PHEBUS, the UV spectrometer onboard BepiColombo, to deduce temperature and production rate of Mg exosphere during each swing-by.

As a result, similar signals were obtained through both swing-bys. Season, local time, and longitude of Mercury during both observations were similar, but boresights of PHEBUS were different (2nd: northward, 3rd: southward). These results show that Mg production rates have little year-to-year variability, which is consistent with the fact that Mg is mainly ejected by micro-meteoroid impact. Besides, these results mean that dust impact flux has little north-south asymmetry.

In this presentation, we introduce the results obtained by observations of the spectrometer onboard BepiColombo, PHEBUS, during the 2nd and 3rd swing-bys. 

How to cite: Suzuki, Y., Quémerais, E., Robidel, R., Chaufray, J.-Y., Murakami, G., Leblanc, F., Yoshioka, K., and Yoshikawa, I.: Comparison of Exospheric Mg Distributions Observed by BepiColombo/PHEBUS During the 2nd and 3rd Mercury Swing-bys, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-798, https://doi.org/10.5194/egusphere-egu24-798, 2024.

The NASA/MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission provided measurements of Mercury’s Ca exosphere, allowing the study of its configuration and its seasonal variations. The observed Ca column densities exhibit a scale height consistent with a temperature > 50,000 K, and with a source located mainly on the dawn-side of the planet. It was suggested that the originating process is due to MMIV (Micro-Meteoroids Impact Vaporization), but previous estimations were not able to justify the observed intensity and energy. The most likely origin of this exospheric element is very probably a combination of different processes involving the release of atomic and molecular surface particles. We use an exospheric Monte Carlo model (Mura et al., 2007) to simulate the 3-D spatial distribution of the Ca-bearing molecule and atomic Ca in the exosphere of Mercury generated by the MMIV process. We investigate the possible pathways to produce the observed Ca exosphere and we discuss about the generating mechanism. Following previous studies, we consider that the atomic Ca in Mercury’s exosphere may be produced in a sequence of different processes: the exospheric energetic Ca component derives from the shock-induced non-equilibrium dissociative ionization and neutralization of Ca+ during the vapor cloud expansion, while a low energy Ca component is generated later by the photo-dissociation of the CaO molecules released by micro-meteoroid impact vaporization. Since the exact temperature, the photolysis lifetimes of the produced molecules and the excess energy during photolysis processes are still not well constrained by observations, we investigate different model assumptions. The theoretical calculations better agree with observations at shorter photolysis lifetimes and higher excess energy of Ca atoms obtained during photolysis of Ca-bearing species. In that case we show the presence of two Ca components: energetic Ca component more intense at high altitudes, and a low energy component in the post-dawn region at low altitudes. The total Ca content obtained through a best fit to the observations shows excess emission near TAA ∼ 25° and TAA ∼150°, which was attributed to the vaporization of surface material induced by the impact of a meteor stream. We investigate the possible contribution due to the comet 2P/Encke for explaining the excess Ca emission at specific orbit positions; the simulation results show some discrepancy when compared to the observations.

How to cite: Moroni, M., MIlillo, A., Mura, A., Plainaki, C., Mangano, V., Aronica, A., Berezhnoy, A., De Angelis, E., Del Moro, D., Di Bartolomeo, P. P., Kazakov, A., Massetti, S., Orsini, S., Rispoli, R., Sordini, R., and Stumpo, M.: Seasonal variation of Ca and Ca-bearing molecules in Mercury's exosphere as a product of micro-meteoroids and comet stream particles impact, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17612, https://doi.org/10.5194/egusphere-egu24-17612, 2024.

Mercury has an extended exosphere that consists of various species. Based on theoretical considerations, the existence of Lithium (Li) in the exosphere around Mercury is predicted to be less than 5x10⁷ cm^-2. Because these density values are well below the detection limits of remote observation instruments on board past missions, Li has never been directly observed. Here we show the first on-site determined altitude-density profile of atomic Li₇, derived from in-situ magnetic field observations by the MESSENGER spacecraft. The results suggest that the source of Li at Mercury is most likely meteoritic ablation. The findings will help to interpret the remote observations of Mercury's exosphere that will be realized in the near future by the BepiColombo mission.

How to cite: Schmid, D., Lammer, H., Volwerk, M., Weichbold, F., Scherf, M., Varsani, A., Roberts, O. W., Simon-Wedlund, C., and Plaschke, F.: First detection of Lithium in Mercury's exosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16068, https://doi.org/10.5194/egusphere-egu24-16068, 2024.

Mercury is known to possess a Magnetosphere that is highly responsive to the upstream Solar Wind conditions. Previous studies using MESSENGER data have contributed to understanding the dynamics of Mercury's respond to the upstream. However, the interactions between the Magnetospheric plasma and the Solar Wind is yet to be fully understood; and it is indeed one of the main focuses of the ESA/JAXA's current mission, BepiColombo. We report the observations of BepiColombo's flyby-3 at Mercury on 19th June 2023, using ion data from SERENA-PICAM and magnetic field data from MAG/MGF instruments. The preliminary analyses have given an insight into the rapidly changing plasma, at the inbound Magnetopause crossing. There is evidence that bursty reconnection could be the main contributor to such dynamic boundary.

How to cite: Varsani, A., Schmid, D., Lammer, H., Nakamura, R., Pump, K., Heyner, D., Laky, G., Jeszenszky, H., Giono, G., Volwerk, M., Milillo, A., Orsini, S., Fischer, D., Magnes, W., Baumjohann, W., and Matsuoka, A.: Bursty reconnection during BepiColombo's third Mercury flyby, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19987, https://doi.org/10.5194/egusphere-egu24-19987, 2024.

On June 19^th 2023, BepiColombo performed its third (MFB3) gravity assist maneuvers at Mercury. During this flyby, the spacecraft approaching the planet from dusk-nightside toward dawn-dayside and traveling down to close distances ~ 235 km altitudes above the planet’s surface. Even though BepiColombo is in a so-called “stacked configuration” during cruise (meaning that most of the instruments cannot be fully operated yet), a number of instruments can still make interesting observations. Particularly, despite their limited field-of-view, the particle sensors allow us to get a hint on the plasma composition and dynamics along a unique path across the magnetosphere and very close to the planet. In this presentation, we will show an overview of the plasma environment from the Mercury Ion Analyzer (MIA) and the Mercury Electron Analyzer (MEA); moreover we will present the first ion composition observations of the Mass Spectrum Analyzer (MSA). MIA, MSA and MEA are part of the Mercury Plasma Particle Experiment (MPPE, PI: Y. Saito) consortium that is a comprehensive instrumental suite for plasma, high-energy particle and energetic neutral atom measurements onboard Mio (Saito et al. 2021). During this flyby, MSA and MIA revealed the presence of energetic (> 10 keV) and cold (< 100 eV) heavy ions inside the magnetosphere around closest approach. Moreover, we will show major features of the Mercury magnetosphere highlighting different regions: 1) plasma sheet, 2) nightside bounday-layer and 3) magnetosheath [Hadid et al., Nature Communications, under review].

How to cite: Hadid, L. and the MSA, MIA and MEA / MPPE teams: Plasma environment of Mercury’s magnetosphere as seen by BepiColombo during its third flyby, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3528, https://doi.org/10.5194/egusphere-egu24-3528, 2024.

The recent swingbys of Mercury by BepiColombo were the first ones ever to pass through the southern magnetosphere, revealing unseen signatures in observational data.

Our electron instrument SORBET/PWI can be used to identify signatures of boundary crossings, such as shock, magnetopause, but also trapped plasma population on closed magnetic field lines in the night side. To bring the observations along the swingbys into a global magnetospheric context, we employ the global 3D magnetohydrodynamic and hybrid models ARMVAC_PLANET (Lesia, l’Observatoire de Paris) and AIKEF (TU Braunschweig/ESA). A new step consists of injecting test particles (especially electrons) in the MHD simulations.

Exploring Mercury's magnetosphere is important both for modeling Mercury's intrinsic magnetic field and for recovering the properties of the upstream IMF once the probe is inside the magnetosphere. These latest results are a major asset for future coordinated observations planned for BepiColombo two spacecraft.

How to cite: Griton, L., Exner, W., Heyner, D., Houeibib, A., Issautier, K., Kasaba, Y., Kojima, H., Moncuquet, M., and Pantellini, F.: Multi-technique investigation of Mercury's southern magnetosphere based on BepiColombo first swingbys, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18888, https://doi.org/10.5194/egusphere-egu24-18888, 2024.

Mercury is the only telluric planet of the solar system, apart from Earth, possessing an intrinsic magnetic field. This magnetic field influences the dynamics of the solar wind plasma impinging on the planet, forming a magnetosphere. Mercury’s magnetosphere has been investigated by multiple space missions in the past, notably the NASA Mariner10 and MESSENGER missions, and is today the target of the joint ESA/JAXA BepiColombo mission, currently en route, with orbit insertion scheduled for December 2025. BepiColombo instruments will observe for the first time the electron kinetic physics at Mercury. In order to interpret and plan BepiColombo’s in-situ observations, an interplay is needed between numerical simulations of Mercury’s magnetosphere and instrumental modelling.

In this work, we present a study of the expected instrumental response of the PWI/AM2P and PWI/SORBET experiments onboard BepiColombo, based on a two-step, fully-kinetic numerical approach.

First, we run fully-kinetic, three-dimensional, global simulations of the interaction between Mercury’s magnetic field and the solar wind using the implicit particle-in-cell code iPIC3D. Non-maxwellian electron distribution functions are observed in the simulations.

Second, we use the electron distribution function derived from the previous step as input for a numerical model of the electric antennas used by both the AM2P and SORBET experiments onboard the JAXA Mio craft (part of BepiColombo). The influence of the spacecraft and antennas geometries is included self-consistently in this second step.

Our 3D full-PIC simulations show that magnetic reconnection in the tail accelerates and heats electrons up to energies of few keVs when the interplanetary magnetic field (IMF) is southward. Such high-energy electrons are ejected from the neutral line in the tail planetward in a substorm-like process, leading to strong particle precipitation in the nightside of Mercury, especially at local time 0-6 h. Double Maxwellian electron distribution functions are inferred from the simulations in the nightside of Mercury (with temperature and density ratio of order 10 and 0.1-1, respectively). We investigate the possibility of detecting these two Maxwellian populations using the AM2P and SORBET experiments, operating at Mercury after orbit insertion. We also explore regions where the AM2P experiment can be calibrated in-flight.

How to cite: Dazzi, P., Lavorenti, F., Henri, P., and Issautier, K.: Mutual impedance and quasi-thermal noise to measure electron properties at Mercury: merging simulations of the magnetosphere and of the instrumental apparatus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13502, https://doi.org/10.5194/egusphere-egu24-13502, 2024.

Observations from the MESSENGER (MErcury Surface, Space Environment, GEochemistry, and Ranging) mission have demonstrated the presence of the region 1-like field-aligned currents (FACs) in Mercury’s northern hemisphere. Due to the limitations of the single-point measurement, the upstream solar wind condition is blind to MESSENGER when it’s inside the magnetosphere. Thus, the statistical analyses of FACs are hard to be carried out and the results could be obscured. Here, we used a hybrid model to investigate Mercury’s FACs. The two-layer model was concerned. We studied how Mercury’s conductivity profile controls the establishment and closure of the FACs, and how the IMF orientation regulated the intensity and the spatial distributions of the FACs. Previous statistical results of MESSENGER’s observations can be well explained by the simulations. And future observations from BepiColombo will help us gain a better understanding of Mercury’s FACs. 

How to cite: Shi, Z., Rong, Z., Fatemi, S., Dong, C., Gao, J., and Wei, Y.: Mercury’s Field-aligned Currents: Hybrid Simulation Results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6904, https://doi.org/10.5194/egusphere-egu24-6904, 2024.

Understanding Mercury's magnetosphere is a primary goal of the BepiColombo mission. In addition to spacecraft observations, numerical modeling efforts have shown to add invaluable insight to the Hermean magnetic field topology, current systems and plasma distributions. However, existing comparisons between observed and modeled data are predominantly qualitative, lacking quantitative agreement due to diverse mathematical approaches. Notably, quantitative inconsistencies of observed and modeled ion densities and energies are particularly affected. Hence, this study addresses systematic and stochastic deviations, focusing on establishing confidence intervals for "ion counting" within the hybrid AIKEF (Adaptive Ion Kinetic Electron Fluid) model. The kinetic treatment of the ions enables to directly compare model results with observations of the Planetary Ion Camera (PICAM), which is a part of the SERENA suite onboard the BepiColombo mission. Multiple ion counting methods are introduced and evaluated, including a simple sphere method, an omnidirectional method, and a field-of-view method. Our findings demonstrate that applying the field-of-view method to the modeled data, within the derived confidence interval, yields ion velocity distributions consistent with PICAM observations of Mercury’s magnetosheath. The AIKEF model and the developed analysis tools serve as a powerful and convenient method of reproducing the ion and electro-magnetic field profile around Mercury for the BepiColombo mission, both in flyby and in-orbit measurements.

How to cite: Teubenbacher, D., Exner, W., Narita, Y., Varsani, A., and Laky, G.: Hybrid plasma simulation around Mercury: ion counting statistics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7659, https://doi.org/10.5194/egusphere-egu24-7659, 2024.

Mercury, the smallest and innermost planet of our solar system, is exposed to a strong solar wind. The internal field is dipole-dominated, relatively weak, axisymmetric and significantly offset towards north. Through the interaction with the strong solar wind, this field leads to a comparatively small and dynamic magnetosphere.

To first order the magnetopause completely separates the magnetosphere from the magnetosheath and thus no magnetic field may penetrate this boundary. In reality, the magnetosheath magnetic field may diffuse across the very thin boundary within a finite time.  We first investigate how the magnetosheath magnetic field changes under different IMF conditions and directions. Second, we can investigate the penetration of the magnetic field from the magnetosheath through the magnetopause inside the magnetosphere and obtain the structure of the IMF influence on the Hermean magnetosphere. 

How to cite: Pump, K., Heyner, D., Plaschke, F., and Exner, W.: Influence of the IMF direction on Mercury's magnetosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9733, https://doi.org/10.5194/egusphere-egu24-9733, 2024.

Here,  we use a state-of-art method to diagnose the Mercury’s dipolar field which is assumed to originate from a magnetic dipole. This method can effectively separate and solve the dipole parameters, and gives the error of how much the dataset of sampled magnetic field deviated from the dipole field . By employing this method and the MESSENGER field data, the derived optimum dipole parameters demonstrated that the dipole center is at [x=5.0;y=-16.0;z=480.5]km, the dipole moment is about M=2.5*10^19 nA.m^2 (or 172 nT*RM^-3), the dipole tilt angle is 3.7 degree. Our yielded dipole moment is weaker than that estimated in previous studies. We compared and discussed with previous studies.

How to cite: Rong, Z.: The non-axial dipolar magnetic field of Mercury, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20477, https://doi.org/10.5194/egusphere-egu24-20477, 2024.

The very low obliquity of Mercury causes important surface temperature variations between its polar and equatorial regions [1]. At the same time, its 3:2 spin orbit resonance leads to longitudinal temperature variations [2]. The combination of these two effects creates a peculiar surface temperature distribution with equatorial hot and warm poles, and cold poles at the geographic poles of the planet. Models that considered the insolation pattern were found compatible with the low-degree shape and geoid from MESSENGER [3]. The models of [3] showed that the insolation pattern imposes a long wavelength thermal perturbation throughout the mantle, whose temperature distribution is strongly correlated with the surface temperature variations. In addition to surface temperature variations, lateral variations of crustal thickness can also affect the temperature distribution of the lithosphere and mantle as it was suggested for Mars [4]. With the topography and gravity data from MESSENGER, a series of models of Mercury’s crustal thickness have been derived assuming constant or variable crustal density, based on the composition of the surface [5].

In this study we include crustal thickness and surface temperature variations of Mercury in the geodynamical code GAIA [6], similar to [4]. We tested several crustal thickness models from [5]. All the simulations are carried in a full 3D spherical geometry, use the extended Boussinesq Approximation, and consider core cooling and radioactive decay. We also use a pressure- and temperature-dependent viscosity in the mantle. The crust is  enriched in heat producing elements (HPEs) compared to the depleted mantle according to a fixed enrichment factor. We model the entire thermal evolution of Mercury to determine the variations of surface and core-mantle boundary heat fluxes in addition to the temporal evolution and distribution of the elastic lithosphere thickness.

Our models indicate that the surface temperature variations of Mercury induce a long-wavelength pattern on both the elastic lithosphere thickness and the heat fluxes, while the crustal thickness variations lead to smaller scale variations of the two quantities. Our models show that different geochemical terranes such as the North Volcanic Plains (NVP) or the High Mg-Region [7] could have experienced drastically different thermal histories throughout the evolution of Mercury.

Future data from the BepiColombo mission [8] will provide a better resolution for the gravity and topography of Mercury, as well as measurements of its surface composition. These data could be used to provide additional estimates of the elastic lithosphere thickness and to constrain the time of formation of the associated geological features. This will help to improve our geodynamical models and in turn constrain Mercury’s thermal evolution.

References:

[1] Margot et al., 2012. [2] Siegler et al., 2013. [3] Tosi et al., 2015. [4] Plesa et al., 2018. [5] Beuthe et al., 2020. [6] Hüttig et al., 2013. [7] Weider et al., 2015. [8] Benkhoff et al., 2021.

How to cite: Fleury, A., Plesa, A.-C., Tosi, N., Walterová, M., and Breuer, D.: Variations of Heat Flux and Elastic Thickness of Mercury derived from Thermal Evolution Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15341, https://doi.org/10.5194/egusphere-egu24-15341, 2024.