Hayley Williamson

During BepiColombo second Mercury’s flyby on 23 June 2022, a ground-based campaign with the THEMIS solar telescope provided simultaneous observations of the sodium (Na) exosphere while Bepicolombo measured interplanetary and magnetospheric conditions. Between 8:53 and 9:34 UT, the exospheric Na emission abruptly increased in intensity by about 70% across the entire day side, followed by a slow recovery to the preceding level over approximately four hours. BepiColombo did not register neither relevant perturbations of the solar wind nor solar energetic particles during the Na increase. The configuration of Mercury, Earth and Solar Orbiter enabled observations of the solar regions facing Mercury from both sides. They revealed that an active region facing Mercury, but hidden from Earth, produced a flare and an extreme-ultraviolet (EUV) brightening when the Na emission increased, whereas subsequent emissions from post-flare loops produced no further increase. While photon-stimulated desorption is one of the main mechanisms releasing Na from the surface, short-therm Na variability has so far been attributed mainly to plasma precipitation. Our observations suggest that solar flares can trigger rapid Na variability at Mercury, and point to a multi-phase release from a finite reservoir of surface sodium, reminiscent of the steeper than linear dependence on solar EUV reported for the Moon on longer timescales. This result marks a significant step forward in understanding the mechanisms governing the interaction of Mercury and the Moon with the Sun and it was possible thanks to multi-messenger observations highlighting the potential of investigations during BepiColombo nominal mission.

A cold dense plasma sheet (CDPS) forms in Earth’s magnetosphere during prolonged northward interplanetary magnetic field (IMF), with both the ionosphere and the solar wind supplying plasma. Mercury lacks a significant ionosphere, offering a natural test of the solar wind’s role, yet whether an analogous CDPS exists there is unknown. Using MESSENGER’s observations and 3D hybrid simulations, we show that Mercury’s plasma sheet is denser, colder, and thicker under northward IMF than under southward IMF. In the MESSENGER data, the mean density doubles (∼ 7.3 vs. ∼ 3.7 cm^-3), the mean ion temperature decreases (∼ 11 vs. ∼ 18 MK), and the thickness more than doubles (∼ 1.53 R_M versus ∼ 0.58 R_M). Hybrid simulations with controlled IMF conditions reproduce these trends. These results demonstrate that a CDPS forms at Mercury without a significant ionosphere, indicating that the CDPS is an intrinsic feature of solar wind interaction with dipolar magnetospheres.

When the upstream Alfvén Mach number is low, the magnetic field may play a dominant role in the solar-wind interaction with Mars, yet the resulting magnetospheric dynamics and associated energy conversion remain poorly constrained. Bulk proton acceleration reaching about 150% of the solar-wind speed is detected jointly by MAVEN, Tianwen-1, and MEX missions in the magnetosheath. The acceleration regions exhibit pronounced asymmetry between the two electric-field hemispheres, defined by the solar-wind electric field, while the shape of the adjacent magnetotail shows axial and hemispheric asymmetries. We demonstrate that the large-scale J×B force, with J denoting the electric current density and B the magnetic field, is the primary driver of acceleration and axial asymmetry. Mass loading of planetary ions introduces strong hemispheric asymmetries—features unique to unmagnetized bodies with atmospheres. Here, we reveal a pathway by which magnetic field converges and redistributes solar-wind energy, and infer that plasma acceleration under low upstream Alfvén Mach number operates not only at Earth but also at Mars and other bodies with magnetosheaths.

The 3DVI (3-D Velocity for Ions) instrument is specifically designed for the M-MATISSE mission to measure, for the first time, the three-dimensional bulk ion velocity in the Martian ionosphere. The instrument consists of two sensor heads: a Retarding Potential Analyzer (RPA) and an Ion Drift Meter (IDM). Both sensors have a field of view defined by a 45° half-cone oriented toward the spacecraft ram direction. By exploiting the spacecraft’s orbital motion, the RPA and IDM determine the bulk ion velocity components parallel and perpendicular to the sensor boresight, respectively, with a sensitivity of 20 m/s.Although sensors of this type have been widely used in previous space missions, their application to the Martian ionosphere requires specific design considerations. These arise primarily from the expected low bulk ion velocities in the lower ionosphere and the low plasma density in the upper ionosphere.A prototype of the 3DVI instrument has been developed and tested using low-energy ion beams. The tests confirmed an angular sensitivity of 0.5° and a field of view of 30° half-cone, in agreement with the instrument requirements. In this presentation, we report and discuss the results of these performance tests.

Mercury's lack of atmosphere allows magnetospheric and solar wind plasma direct access to the surface through precipitation, altering the surface and plasma composition. In this way, its space plasma environment interactions resemble that of the Moon. Lunar measurements show that such exposed surfaces are subject to electrostatic charging, where photoelectrons generated on the dayside creating a positive potential of a few V, while electron transport to the nightside induces a negative surface potential up to -100s V. Given Mercury's similar surface properties and long diurnal cycle, we expect a similar pattern in surface potential; indeed, the nightside potential is likely even more negative at Mercury than at the Moon due to high energy electron precipitation.Lunar Prospector electron reflectrometry data indicates that this surface potential can be estimated remotely from pitch angle distributions of reflected particles, as the potential adds an energy-dependent term to the particle loss cone [1]. For positively charged ions and a negative surface potential, the size of the upward loss cone becomes inversely proportional to ion energy and can include all pitch angles < 90 degrees for sufficiently negative potentials. Thus, this effect has important implications for the ability of Mercury's magnetic field to trap particles on the nightside. We examine nightside pitch angle distributions from the Miniature Ion Precipitation Analyzer (MIPA) in the SERENA package from BepiColombo's second Mercury flyby for evidence of this loss cone energy dependence and find a noticeably visible effect for upward-going ions. Lunar surface potential analysis shows a strong dependence on electron temperature [2], so we use Mercury Electron Analyzer (MEA) electron temperature measurements from MFB2 [3] as a basis for fitting the loss cone and find good agreement with the MIPA data. This case study shows that estimation of surface potential from ion measurements is indeed possible, and promises interesting results to come from the BepiColombo orbital phase.[1] Halekas, J. S., G. T. Delory, R. P. Lin, T. J. Stubbs, and W. M. Farrell. “Lunar Prospector Observations of the Electrostatic Potential of the Lunar Surface and Its Response to Incident Currents.” JGR: Space Physics 113, no. A9 (2008). https://doi.org/10.1029/2008JA013194.[2] Stubbs, T. J., W. M. Farrell, J. S. Halekas, et al. “Dependence of Lunar Surface Charging on Solar Wind Plasma Conditions and Solar Irradiation.” P&SS 90 (January 2014): 10–27. https://doi.org/10.1016/j.pss.2013.07.008.[3] Rojo, M., N. André, S. Aizawa, et al. “Structure and Dynamics of the Hermean Magnetosphere Revealed by Electron Observations from the Mercury Electron Analyzer after the First Three Mercury Flybys of BepiColombo.” A&A 687 (July 2024): A243. https://doi.org/10.1051/0004-6361/202449450.

Context. Rosetta followed comet 67P at heliocentric distances from 1.25 to 3.6 au. Close to perihelion, Rosetta was located in the solar wind ion cavity, with only sporadic observations of solar wind ions. Just outside the solar wind ion cavity, the solar wind ion-flow direction was mainly sunward. Aims. We aim to study the evolution of solar wind interaction with a comet as its scale size increases from sub-ion gyroradius to above the proton gyroradius. The former was observed at 67P during most of the Rosetta mission. The latter was observed during sporadic solar wind encounters around perihelion. Methods. We analysed particle data from the mass-resolving ion spectrometer ICA, searching for the weak and sporadic occurrences of solar wind ions close to perihelion. All Rosetta plasma data were used to understand the plasma parameter regime of the observed interaction. Results. At comet 67P, we observe the transition from solar wind interaction during the first partial gyration of the solar wind ions in the slowed-down plasma around the comet to multiple gyrations in an interaction region larger than the proton gyroradius. During the multiple-gyration stage, the protons show a consistent pattern of motion ordered by the direction of the solar wind electric field. In the hemisphere where the electric field points away from the nucleus, the protons move sunward. They move anti-sunward in the opposite hemisphere. This can be explained by simple trochoid trajectories and a strong density gradient. Under the same conditions, the water ions also show a consistent flow pattern relative to the electric field determined by the point in their gyration at which they pass closest to the nucleus. Protons are slowed down and heated, which is consistent with a shock upstream. The plasma beta is close to one, and the magnetosonic Mach number was typically less than unity.

We examine the first three BepiColombo Mercury flybys Using data from the Miniature Ion Precipitation Analyzer (MIPA), an ion mass analyzer in the Search for Exospheric Refilling and Natural Abundances package on the Mercury Planetary Orbiter designed to study magnetospheric dynamics. These flybys all passed from dusk to dawn through the nightside equatorial region but were noticeably different from each other. In the first flyby, we observe a low latitude boundary layer and 1 keV ions near closest approach. For flybys 2 and 3 we see ions up to 14 keV in the same location, including freshly injected precipitating ions inside the loss cone. High time resolution data from flyby 3 show variations consistent with bursty bulk flows 10s long and occurring over s periods, the first such observation in this region. MIPA data demonstrate that high‐energy injection processes are an important source of precipitation ions at Mercury.

We examine the first three BepiColombo Mercury flybys Using data from the Miniature Ion Precipitation Analyzer (MIPA), an ion mass analyzer in the Search for Exospheric Refilling and Natural Abundances (SERENA) package on the Mercury Planetary Orbiter (MPO) designed to study magnetospheric dynamics. These flybys all passed from dusk to dawn through the nightside equatorial region but were noticeably different from each other. In the first flyby, we observe a low latitude boundary layer and $\sim$1 keV ions near closest approach. For flybys 2 and 3 we see ions up to 14 keV in the same location, including freshly injected precipitating ions inside the loss cone. High time resolution data from flyby 3 show variations consistent with bursty bulk flows 10s long and occurring over $\sim30$s periods, the first such observation in this region. MIPA data demonstrate that high-energy injection processes are an important source of precipitation ions at Mercury.

BepiColombo, the joint ESA/JAXA mission to Mercury, was launched in October 2018 and is scheduled to arrive at Mercury in November 2026 after an 8-year cruise. Like other planetary missions, its scientific objectives focus mostly on the nominal, orbiting phase of the mission. However, due to the long duration of the cruise phase covering distances between 1.2 and 0.3 AU, the BepiColombo mission has been able to outstandingly contribute to characterise the solar wind and transient events encountered by the spacecraft, as well as planetary environments during the flybys of Earth, Venus, and Mercury, and contribute to the characterisation of the space radiation environment in the inner Solar System and its evolution with solar activity. In this paper, we provide an overview of the cruise observations of BepiColombo, highlighting the most relevant science cases, with the aim of demonstrating the importance of planetary missions to perform cruise observations, to contribute to a broader understanding of Space Weather in the Solar System, and in turn, increase the scientific return of the mission. Graphical Abstract

The European Space Agency’s (ESA) Mars Express (MEX) mission to Mars has been returning valuable scientific data for 21+ years. This data is available to the public for free via the Planetary Science Archive (PSA), which houses the raw, calibrated, and higher-level data returned by the ESA’s planetary missions, including data provided by the various MEX instrument teams. The Analyzer of Space Plasma and Energetic Atoms 3 (ASPERA-3) has provided several types of datasets throughout the mission, focusing on the ions and electrons in Mars' ionosphere as well as out into the solar wind environment surrounding Mars. For the Ion Mass Analyzer (IMA) subinstrument, the ASPERA-3 team has provided new level 4 and level 5 datasets which cover nearly the entirety of MEX's mission lifetime. The level 4 sets contain data products covering the differential number flux of H+, He++, O+, and O2+ (in units of m-2 s-1 sr-1 eV-1) for the various sectors of the IMA detector. The level 5 sets contain data products combining all the IMA sectors' data to yield temperature (eV), density (cm-3), and velocity (km s-1) information on these same 4 ion species. All this data and more can be accessed at the PSA at: https://archives.esac.esa.int/psa/Mars Express: MEX was inserted into Mars orbit in December 2003, though several instrument test observations also exist from the cruise phase of the mission, prior to arrival at Mars. Thus, this long-lived Mars mission covers 21+ years of data with its 7 instruments. Later in the mission’s lifetime, the camera used for the Beagle 2 lander separation was reactivated and used for public outreach. Over time, the camera began to be used for scientific observations as well, making MEX an unusual mission in that with this addition of the VMC instrument it now has more scientific instruments in operation than it was launched with.The PSA user interface: The ESA’s PSA uses the Planetary Data System (PDS) format developed by NASA to store the data from its various planetary missions. In the case of MEX, the data is stored in the PDS3 format, which primarily uses ASCII files to store and describe the data. Newer missions, from ExoMars onward use the PDS4 data standard, which uses XML files to store the label information. There are three primary ways in which to find the data. One is the FTP area, which houses all the public data in the PSA. Here, there are no advanced search capabilities, but it does provide access to all the supporting files and documentation for the various datasets. When first searching for new data, users would benefit from using the Table View search interface [1]. Here the user can search using various parameters, such as mission name, target, instrument name, processing level, observation times, etc. The Table View is also linked to the Image View, where users can view the browse images provided by the PI teams. The Table View interface also has a section for “Free Search”, allowing one to use Contextual Query Language (CQL) to search over additional parameters. These various search methods rely in part on the metadata provided by the instrument teams in the labels associated with each of the data products. Finally, there is also a Map View for viewing the footprints of data from those instruments where such calculations can be of some utility. This Map View is built using GIS tools.Conclusion: The delivery of the ASPERA-3 data provides new high level data on the ion populations in the vicinity of Mars. This data can be freely accessed at the ESA’s PSA, at https://archives.esac.esa.int/psa/. There are multiple ways of browsing the ASPERA-3 and other instrument teams’ data, including from other planetary missions, which will be explained in this poster. The development of the PSA’s user interface is an ongoing project, and we welcome feedback from the community for suggestions on new ways to search this wealth of data. Feedback and suggestions can be sent via our Help Desk system at:https://support.cosmos.esa.int/psa/Acknowledgements: The MEX Support Archive Scientists and the entire PSA team would like to extend their thanks to the ASPERA-3 team for their effort in continuing to deliver new data from Mars to the public via ESA’s PSA. Our thanks go also to the European taxpayers, whose contributions to the European Space Agency enable the gathering and dissemination of this scientific knowledge, and preserving it for future generations of scientists to work on.References: [1] Besse S. et al. (2018) Planetary and Space Science, 150, 131-140.