Search

At Mercury, several processes can release ions and neutrals out of the planet's surface. Here we present enhancements of planetary ions (Na+‐group ions) in Mercury's northern magnetospheric cusp during flux transfer event (FTE) "showers." FTE showers are intervals of intense dayside magnetopause reconnection, during which FTEs are observed in quick succession, that is, only separated by a few seconds. This study identifies 1953 FTE shower intervals and 1795 Non‐FTE shower intervals. During the shower intervals, this study shows that the FTEs form a solar wind entry layer equatorward of the northern magnetospheric cusp. In this entry layer, solar wind ions are accelerated and move downward (i.e., planetward) toward the cusp, which sputter upward‐moving planetary ions with a particle flux of 1 × 1011 m−2 s−1 within 1 min. The precipitation rate is estimated to increase by an order of magnitude during FTE showers, to 2 × 1025 s−1, and the neutral density of the exosphere could vary by >10% in response to this FTE‐driven sputtering. Such rapid large‐scale variations driven by dayside reconnection may explain the minute‐to‐minute changes in Mercury's exosphere, especially on the high latitudes, observed by ground‐based telescopes on Earth. Our MESSENGER in situ observation of enhanced planetary ions in the entry layer likely corresponds to an escape channel for Mercury's planetary ions. Comprehensive, future multipoint measurements made by BepiColombo will greatly enhance our understanding of the processes contributing to Mercury's dynamic exosphere and magnetosphere. Plain Language Summary: For the airless objects in the solar system, energetic ion sputtering is an important process that can release particles out of the planet's surface. In Mercury's magnetosphere, the solar wind energetic ions have been suggested to be able to release neutrals out of the surface in a short period by models and simulations. This paper has examined the 4 years of magnetic field and plasma measurements collected by NASA's MESSENGER mission orbiting Mercury and has led to the discovery of how reconnection between the interplanetary and planetary magnetic fields leads to the formation of solar wind entry layers around Mercury's magnetospheric cusps. These entry layers act as magnetic channels that cause the solar wind energetic ions to move downward toward the planet and precipitate onto the surface beneath Mercury's northern and southern magnetospheric cusps where they sputter neutral sodium and sodium ions. This paper concludes that the solar wind sputtering could account for 10% or greater changes in the density of neutral sodium in Mercury's exosphere, and the sputtered sodium ions likely form an escape channel of Mercury's planetary species. The ion escape depended on the solar wind driving magnetopause reconnection at Mercury is different from the ion escape at Venus and Mars, where escape ions are ionized by the solar ultraviolet (UV). Key Points: Solar wind entry layer is observed to form equatorward of cusp during flux transfer event showers which enhances precipitation rate by an order of magnitudeSolar wind sputtering can release planetary ions and neutrals efficiently within 1 min of the onset of magnetopause reconnectionA new escape channel for planetary ions is formed by solar wind sputtering with an escape rate of ∼1024 s−1 for Na+‐group ions [ABSTRACT FROM AUTHOR]

We analyzed Mars Atmosphere and Volatile Evolution (MAVEN) and Venus Express (VEX) data of magnetic flux ropes observed in both Mars and Venus nightside induced magnetosphere, in order to understand their statistical characteristics and possible formation processes. We statistically identified 382 (286) events at Mars (Venus) via the minimum variance analysis and investigated the flux rope properties including their geometrical configurations of axial core field direction and spatial distributions. Interestingly, there is no significant difference with respect to the variety of the flux rope axial orientation between Mars and Venus, indicating that about at least one fourth of events do not necessitate magnetotail reconnection for their formations. However, the spatial distribution shows that flux ropes at Venus tend to be observed near the central plasma sheet, whereas those at Mars are more spread out. Moreover, the events tend to be observed more frequently in the -E hemisphere, where the solar wind electric field (ESW) is pointing toward the planet, rather than in +E hemisphere, where the ESW direction is away from the planet. The geographical distribution shows that flux ropes at Mars tend to be observed more frequently in the southern hemisphere where the strong crustal magnetic fields are primarily distributed. Therefore, such a tendency indicates that the Martian crustal magnetic fields could play significant roles on generating flux ropes in the nightside magnetosphere of Mars. [ABSTRACT FROM AUTHOR]

Data collected by the Fast Imaging Plasma Spectrometer (FIPS) aboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft showed singly charged Na+‐group ions at energies of between 1 and 13 keV in Mercury's northern planetary cusp. Most of these ions are likely formed by either photoionization or charge exchange of exospheric Na atoms, with initial energies of approximately 1 eV or less. FIPS observations did not establish which acceleration mechanism most reasonably accounts for this energy gain. Using the Adaptive Mesh Particle Simulator (AMPS) model, we undertake kinetic simulations of 1 eV Na+ test particles through the electric and magnetic fields output from the Block Adaptive Tree Solar wind Roe‐type Upwind Scheme (BATSRUS) global magnetohydrodynamic (MHD) model of Mercury's magnetosphere, in search of plausible explanations for the source of this energization. We find that Na+ with initial energy of 1 eV are readily picked up by the Dungey cycle return flow in the dayside magnetosphere. In some cases, this flow provides the energy for the ions to escape into the magnetosheath, and in other cases it energizes the ions to hundreds of eV before they pass immediately into the cusp. Those that escape can be rapidly picked up into the magnetosheath flow, where they are accelerated by pickup again up to tens of keV. These one‐ and two‐stage pickup processes on Mercury's dayside can account for the energies of many of the Na+ ions observed in Mercury's northern magnetospheric cusp by MESSENGER. Plain Language Summary: Data collected in orbit at Mercury showed sodium ions in the northern planetary cusp at high energies. The processes that likely create these ions are only responsible for 0.01%–0.1% of that high energy, and no mechanism previously known to operate at Mercury can account for the difference. We model the Mercury system, and the paths of ions through that system, in search of such a mechanism. We find two mechanisms, both involving energization into proton flows, that explain the data observations. Key Points: Sodium ions (Na+) with initial energy of 1 eV are energized by Dungey cycle return flow in the dayside dipolar regionNa+ are not trapped within the dayside dipolar region of MercuryOne‐ and two‐stage pickup processes can energize Na+ up to tens of keV entirely on the dayside [ABSTRACT FROM AUTHOR]

In this study, we have analyzed Mars Atmosphere and Volatile EvolutioN (MAVEN) observations of fields and plasma signatures associated with an encounter of fully developed Kelvin–Helmholtz (K–H) vortices at the northern polar terminator along Mars' induced magnetosphere boundary. The signatures of the K–H vortices event are: (a) quasi‐periodic, "bipolar‐like" sawtooth magnetic field perturbations, (b) corresponding density decrease, (c) tailward enhancement of plasma velocity for both protons and heavy ions, (d) co‐existence of magnetosheath and planetary plasma in the region prior to the sawtooth magnetic field signature (i.e., mixing region of the vortex structure), and (e) pressure enhancement (minimum) at the edge (center) of the sawtooth magnetic field signature. Our results strongly support the scenario for the non‐linear growth of K–H instability along Mars' induced magnetosphere boundary, where a plasma flow difference between the magnetosheath and induced‐magnetospheric plasma is expected. Our findings are also in good agreement with 3‐dimensional local magnetohydrodynamics simulation results. MAVEN observations of protons with energies greater than 10 keV and results from the Walén analyses suggests the possibility of particle energization within the mixing region of the K–H vortex structure via magnetic reconnection, secondary instabilities or other turbulent processes. We estimate the lower limit on the K–H instability linear growth rate to be ∼5.84 × 10−3 s−1. For these vortices, we estimate the instantaneous atmospheric ion escape flux due to the detachment of plasma clouds during the late non‐linear stage of K–H instability to be ∼5.90 × 1026 particles/s. Extrapolation of loss rates integrated across time and space will require further work. Key Points: Mars Atmosphere and Volatile EvolutioN (MAVEN) observed magnetic field and plasma signatures consistent with the encounter of fully developed Kelvin–Helmholtz (K–H) vortices along Mars' induced magnetospheric boundary (IMB)Close agreement between 3‐D magnetohydrodynamics simulation result and MAVEN observation support the scenario for K–H instability occurrence along Mars' IMBWe estimated the instantaneous atmospheric ion escape flux due to detachment of plasma clouds from K–H instability to be ∼5.9 × 1026 s−1 [ABSTRACT FROM AUTHOR]

Mercury is embedded in a tenuous and highly anisotropic sodium exosphere, generated mainly by plasma‐surface interactions. The absolute values of the sodium ion density are still under debate. Observations by MESSENGER's Fast Imaging Plasma Spectrometer (FIPS) instrument suggest the density of exospheric ions to be several orders of magnitude lower than the upstream solar wind density, indicating that the sodium exosphere has no substantial influence on the magnetospheric current systems. However, MESSENGER magnetic field observations of field line resonances revealed sodium ion densities comparable to the upstream solar wind density. To investigate how a dense exosphere would affect the current systems within Mercury's magnetosphere, we apply an established hybrid (kinetic ions, fluid electrons) model and conduct multiple model runs with gradually increasing exospheric density, ranging from no sodium ions at all to comet‐like configurations. We demonstrate how a sufficiently dense exosphere leads to self‐shielding of the sodium ion population from the ambient electric field and a significant inflation and symmetrization of Mercury's magnetosphere, which is decreasingly affected by the dipole offset. Once the sodium ion density is sufficiently high, Region 2 field‐aligned currents emerge close to the planet. The modeled Region 2 currents are located below the orbit of MESSENGER, thereby providing a possible explanation for the absence of these currents in observations. The sodium exosphere also closes a significant fraction of the Region 1 currents through Pedersen and Hall currents before the "guiding" magnetic field lines even reach the planetary surface. The modeled sodium ion and solar wind densities agree well with observations. Key Points: A hybrid model is applied to study the influence of Mercury's sodium exosphere on the currents in the magnetosphereA dense sodium exosphere based on Gamborino et al. (2019) partially closes Region 1 currents before they reach the dayside surfaceWith a dense sodium exosphere included, Region 2 currents can form below the altitude of MESSENGER's orbit [ABSTRACT FROM AUTHOR]

The Galilean moons play major roles in the giant magnetosphere of Jupiter. At the same time, the magnetospheric particles and fields affect the moons. The impact of magnetospheric ions on the moons' atmospheres supplies clouds of escaping neutral atoms that populate a substantial fraction of their orbits. At the same time, ionization of atoms in the neutral cloud is the primary source of magnetospheric plasma. The stability of this feedback loop depends on the plasma/moon‐atmosphere interaction. The purpose of this review is to describe the physical processes that shape the space environment around the two innermost Galilean moons—Io and Europa—and to show their impact from the planet Jupiter out into interplanetary space. Key Points: Io and Europa substantially impact the Jovian magnetosphere while interactions of plasma with moons affects their surfaces and atmospheresTen components are described, including neutrals, thermal plasma, and energetic particles, spanning from Jupiter to interplanetary mediumCurrent understanding of the systems and processes are reviewed with a summary of outstanding questions [ABSTRACT FROM AUTHOR]

This study presents a survey of ion flow speed, density, temperature, and composition observed by the Jovian Auroral Distributions Experiment Ion (JADE‐I) sensor on Juno from 10–40 RJ in the dawn to midnight sector of Jupiter's magnetosphere. The survey covers Juno orbits 5–22, and the observations are separated by equatorial (|zmag[RJ]| ≤ 1.5) and off‐equator (|zmag[RJ]|>1.5) regions. Plasma parameters for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+ are derived by forward modeling JADE‐I's energy‐per‐charge versus time‐of‐flight spectra using omnidirectional averaged convected kappa distributions and modeled instrument responses. O+ and S2+ are resolved via a ray‐tracing simulation based on carbon‐foil‐effects. The ion flow speed increases with radial distance and is comparable to rigid corotation speed out to ∼20 RJ. Ion number densities decrease with radial distance, the primary species being H+, O+, and S2+. The relative contribution of H+ and S2+ increases and decreases, respectively, in the off‐equator regions, supporting the interpretation that the latitudinal distribution of ions is mass dependent. The O+ to S2+ and ΣOn+ to ΣSn+ number density ratios are variable, the 5 RJ bin averages for O+ to S2+ ranging from ∼0.75–1.5 (equator) and ∼1.1–1.8 (off‐equator) and ΣOn+ to ΣSn+ from ∼0.6–0.9 (equator) and ∼0.8–1.1 (off‐equator). Both proton and heavy ion temperatures show order of magnitude increases between 10 and 20 RJ and range from ∼100 eV to 10 keV and 1 keV to a few tens of keV, respectively. Plain Language Summary: The Jovian Auroral Distributions Experiment (JADE) on Juno has continuously investigated the plasma environment in Jupiter's magnetosphere since its arrival in August 2016. The polar‐orbiting spacecraft enables JADE to explore both equatorial and off‐equator regions of Jupiter's plasma sheet. In this study, we present plasma sheet ion characteristics such as ion composition, flow speed, and temperatures for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+ that are originating from the innermost Galilean satellite Io. A spatial dependence of ion characteristics is discussed and compared to previous observations. While the density profiles agree well with the Voyager‐based studies, temperatures found in this study show at least an order of magnitude higher values. A new addition to this paper is that the latitudinal distribution of ions shows trend in the mass. Relative composition of protons increases compared to the heavier ions in the off‐equator regions. These observations provide insights on how the ions are distributed throughout Jupiter's magnetosphere and improve our current understanding on ion dynamics in the plasma sheet. Key Points: Ion flow speed, number density, temperature, and composition in Jupiter's plasma sheet show radial and/or latitudinal trendsH+, O+, and S2+ are the primary ions, the contribution of H+ and S2+ increasing and decreasing, respectively, in the off‐equator regionThe O+ to S2+ density ratio is variable, the 5 RJ bin averages ranging from 0.7–1.5 (equator) and 1.1–1.8 (off‐equator) [ABSTRACT FROM AUTHOR]

Titan's magnetic environment is a dynamic and unique place. We detect 85 flux ropes during all the Cassini flybys of Titan from 2005–2017. Analysis describing the location of flux ropes in Titan's ionosphere as well as where Titan is in Saturn's magnetosphere shows that the flux ropes are more often found when Titan is in the noon sector of Saturn's magnetosphere. A secondary peak of occurrence is found in the postmidnight area, where it is expected that Saturn's magnetosphere is highly dynamic. We also find that the flux rope occurrence is correlated with the average electron density profile of Titan's ionosphere. A force‐free model is utilized to estimate the radii and core magnetic field strength of the flux ropes. We find a large range of radii from 150–500 km with a small number of very large flux ropes (500–1,000 km) and a range of core field strengths of 1–15 nT, again with some much larger values(20–40 nT). The model also shows that more flux ropes are right‐handed than left‐handed in twist; however, we are unable to determine if there is a physical reason or if this is due to an observer bias. Additionally, we evaluate the goodness of fit for the model in each instance and conclude that, on average, the flux ropes may be better represented by a non‐force‐free model. Key Points: Eighty‐five flux ropes are detected in Titan's ionosphere using all of Cassini's flybys of TitanFlux ropes are present when Titan is in dynamic areas of Saturn's magnetosphereFitting a force‐free flux rope model leads to the conclusion that on average they are unlikely to be force free [ABSTRACT FROM AUTHOR]

We examine the effects of the interplanetary magnetic field (IMF) orientation and solar wind dynamic pressure on the solar wind proton precipitation to the surface of Mercury using a hybrid‐kinetic model. We use our model to explain observations of Mercury's neutral sodium exosphere and compare our results with MESSENGER observations. For the typical solar wind dynamic pressure at Mercury our model shows a high proton flux precipitates through the magnetospheric cusps to the high latitudes on both hemispheres on the dayside, centered near the noon meridian with ∼11° latitudinal extent in the north and ∼21° latitudinal extent in the south, which is consistent with MESSENGER observations. We show that this two‐peak pattern is controlled by the radial component (Bx) of the IMF and not the Bz. Our model suggests that the southward IMF and its associated magnetic reconnection do not play a major role in controlling plasma precipitation to the surface of Mercury through the cusps. We found that the total precipitation rate through both of the cusps remain constant and independent of the IMF orientation. We also show that the solar wind proton incidence rate to the entire surface of Mercury is higher when the IMF has a northward component and nearly half of the incidence flux impacts the low latitudes on the nightside. During extreme solar events (e.g., coronal mass ejections), our model suggests that over 70 nPa solar wind dynamic pressure is required for the entire surface of Mercury to be exposed to the solar wind plasma. Key Points: Radial component of the IMF controls the precipitation patterns to the surfaceProton incidence rate to the entire surface is higher when the IMF has a northward componentSum of the incidence rate through both cusps remains constant for different IMF orientations [ABSTRACT FROM AUTHOR]

Mercury's nightside magnetosphere is investigated under the impact of a coronal mass ejection (CME) and a high‐speed stream (HSS) with MErcury Surface, Space ENviroment, GEochemistry, and Ranging (MESSENGER) observations. The CME was shown to produce a low plasma β (ratio of thermal pressure to magnetic pressure) magnetosheath, while the HSS creates a higher β magnetosheath. Reconnection at the dayside magnetopause was found to be stronger during the CME than the HSS, but both were stronger than the average condition (Slavin et al., 2014, https://doi.org/10.1002/2014JA020319). Here we show that the CME and HSS events produced large numbers of flux ropes and dipolarization fronts in the plasma sheet. The occurrence rates for the structures were approximately 2 orders of magnitude higher than under average conditions with the rates during CME's being twice that of HSS's. The flux ropes appeared as quasiperiodic flux rope groups. Each group lasted approximately 1 min and had a few large flux ropes followed by several smaller flux ropes. The lobe magnetic flux accounted for around half of the Mercury's available magnetic flux with the flux during CME's being larger than that of HSS's. The CME produced a more dynamic nightside magnetosphere than the HSS. Further, for the CME event, the tail magnetic reconnection produced a distorted Hall magnetic field pattern and the X‐line had a dawn‐dusk extent of 20% of the tail width. No magnetic flux loading and unloading events were observed suggesting that, during these intense driving conditions, Mercury's magnetosphere responded with a type of quasi‐steady convection as opposed to the tail flux loading‐unloading events seen at Earth. Key Points: Coronal mass ejections drive more intense nightside reconnection than high speed streamsUnder extreme conditions, magnetic reconnection produces a distorted Hall magnetic field pattern in the plasma sheetContinued intense solar wind forcing does not produce substorm magnetic flux loading and unloading of tail lobe instead steady convection [ABSTRACT FROM AUTHOR]

The Jovian Auroral Distributions Experiment Ion sensor (JADE‐I) on Juno is a plasma instrument that measures the energy‐per‐charge (E/Q) distribution of 0.01 to 46.2 keV/q ions over a mass‐per‐charge (M/Q) range of 1– 64 amu/q. However, distinguishing O+ and S2+ from JADE‐I's measurements is a challenging task due to similarities in their M/Q (∼16 amu/q). Because of this, O+ and S2+ have not been fully resolved in the in situ measurements made by plasma instruments at Jupiter (e.g., Voyager PLS and Galileo PLS) and their relative ratios has been studied using physical chemistry models and ultraviolet remote observations. To resolve this ambiguity, a ray tracing simulation combined with carbon foil effects is developed and used to obtain instrument response functions for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+. The simulation results indicate that JADE‐I can resolve the M/Q ambiguity between O+ and S2+ due to a significant difference in their charge state modification process and a presence of a large electric potential difference (∼8 kV) between its carbon foils and MCPs. A forward model based on instrument response functions and convected kappa distributions is then used to obtain ion properties at the equatorial plasma sheet (∼36 RJ) in the predawn sector of magnetosphere. The number density ratio between O+ and S2+ for the selected plasma sheet crossings ranges from 0.2 to 0.7 (0.37 ± 0.12) and the number density ratio between total oxygen ions to total sulfur ions ranges from 0.2 to 0.6 (0.41 ± 0.09). Key Points: A technique to resolve mass‐per‐charge ambiguity of O+ and S2+ for ESA‐TOF instruments using carbon foil effectsAn analysis tool to extract ion distributions from in situ measurements of Juno JADE‐IIon bulk properties derived from the forward model with convected kappa distributions in the jovian plasma sheet [ABSTRACT FROM AUTHOR]

Magnetic flux ropes (MFRs) with twisted magnetic field lines are common in the solar system, most of which can be caused by magnetic reconnection or velocity shear. However, these two mechanisms have difficulties in explaining the formation of MFRs observed in the planetary ionosphere. Here we find that a dynamo process can be caused by the differential compression at different parts of a flux tube when it is sinking into the partially ionized ionosphere, leading to an increase in the magnetic energy. The differential compression also produces an azimuthal component of ▽×E, which generates azimuthal magnetic fields with twisted magnetic field lines and gives rise to an ionospheric MFR. Key Points: The differential compression of flux tube at different altitudes provides a dynamo process to increase the tube magnetic energyAzimuthal magnetic fields can be generated by (▽×E)ϕ associated with the differential compressionThe flux tube is twisted in different directions with opposite helical pitch angles on the two sides of the flux tube [ABSTRACT FROM AUTHOR]

The interaction between the Io plasma torus and Io exhibits significant dynamics resulting from temporal variations of both external conditions in the plasma torus and local conditions in Io's environment. We present analysis of an extensive simulation campaign of the Io plasma interaction under varying interaction conditions performed by using a hybrid multispecies simulation model. We test two models of electron impact ionization, one resulting in plasma production constrained to the upstream hemisphere of Io and the other producing a more symmetric distribution of the plasma with nonnegligible plasma production on the downstream side of Io. In the latter case, the simulation model provides high level of agreement with Galileo measurements of magnetic field obtained during the I0 flyby, where the model captures even smaller‐scale features of the magnetic field profile. Our simulated results provide strong support for the existence of Io's induced dipole field. In this model we assume that induced dipole field moment is antiparallel to the direction of the inducing magnetic field, equivalent to induction in a highly conductive Io. Our results further support the idea that Io's atmosphere collapsed during the Galileo I27 flyby, which manifests itself in the lack of ion heating due to pickup processes in the extended atmosphere. Our results show that the dominant torus species, O+ and S++, are depleted around Io and may exhibit temperature anisotropy, T⊥/T‖ < 1, resulting from merging of ion populations coming from opposite sides of Io along the magnetic field. Key Points: A nonnegligible ion source on the downstream side of Io is required to explain Galileo observationsSimulated results provide strong support for the existence of Io's induced dipole fieldDominant torus species have parallel temperature exceeding the perpendicular temperature close to Io [ABSTRACT FROM AUTHOR]

Previous missions to Venus have revealed that encounters with plasma irregularities of atmospheric origin outside the atmosphere are not uncommon. A number of mechanisms have been proposed to discuss their origins as well as their roles in the atmospheric evolution of Venus. One such mechanism involves an ionopause with a wavelike appearance. By utilizing the magnetic field and plasma data from Venus Express, we present the first observational statistical analysis of the ionospheric boundary wave phenomena at Venus using data from 2006 to 2014. Results from the minimum variance analysis of all the photoelectron dropout events in the ionosphere reveal that the ionopause of Venus does not always appear to be smooth but often exhibits a wavelike appearance. In the northern polar region of Venus, the normal directions of the rippled ionospheric boundary crossings lie mainly in the terminator plane with the largest component predominantly along the dawn‐dusk (YVSO) direction. The average estimated wavelength of the boundary wave is 212 ± 12 km, and the average estimated velocity difference across the ionopause is 104 ± 6 km/s. The results suggest that the rippled boundary is a result of Kelvin‐Helmholtz instability. Analysis reveals a correlation between the normal directions and the locations of the boundary wave with respect to Venus. This indicates that the draping of magnetic field lines may play a role in enhancing the plasma flow along the dawn‐dusk direction, which could subsequently set up a velocity shear that favors the excitation of ionospheric boundary wave by the Kelvin‐Helmholtz instability along the dawn‐dusk direction. Key Points: The ionospheric boundary is not always smooth; it is often observed to exhibit a wavelike appearanceCharacteristics of the boundary wave are consistent with a Kelvin‐Helmholtz instability‐induced waveDraping patterns of magnetic field lines set up favorable conditions for boundary wave excitation [ABSTRACT FROM AUTHOR]

Abstract: We analyze 94 traversals of Mercury's southern magnetospheric plasma mantle using data from the MESSENGER spacecraft. The mean and median proton number densities in the mantle are 1.5 and 1.3 cm−3, respectively. For sodium number density these values are 0.004 and 0.002 cm−3. Moderately higher densities are observed on the magnetospheric dusk side. The mantle supplies up to 1.5 × 108 cm−2 s−1 and 0.8 × 108 cm−2 s−1 of proton and sodium flux to the plasma sheet, respectively. We estimate the cross‐electric magnetospheric potential from each observation and find a mean of ~19 kV (standard deviation of 16 kV) and a median of ~13 kV. This is an important result as it is lower than previous estimations and shows that Mercury's magnetosphere is at times not as highly driven by the solar wind as previously thought. Our values are comparable to the estimations for the ice giant planets, Uranus and Neptune, but lower than Earth. The estimated potentials do have a very large range of values (1–74 kV), showing that Mercury's magnetosphere is highly dynamic. A correlation of the potential is found to the interplanetary magnetic field (IMF) magnitude, supporting evidence that dayside magnetic reconnection can occur at all shear angles at Mercury. But we also see that Mercury has an Earth‐like magnetospheric response, favoring −BZ IMF orientation. We find evidence that −BX orientations in the IMF favor the southern cusp and southern mantle. This is in agreement with telescopic observations of exospheric emission, but in disagreement with modeling. [ABSTRACT FROM AUTHOR]

A simple Monte Carlo model is presented that considers the effects of spacecraft orbital sampling on the inferred distribution of magnetic flux ropes, generated through magnetic reconnection in the magnetotail current sheet. When generalized, the model allows the determination of the number of orbits required to constrain the underlying population of structures: It is able to quantify this as a function of the physical parameters of the structures (e.g., azimuthal extent and probability of generation). The model is shown adapted to the Hermean magnetotail, where the outputs are compared to the results of a recent survey. This comparison suggests that the center of Mercury's neutral line is located dawnward of midnight by 0.37−1.02+1.21RM and that the flux ropes are most likely to be wide azimuthally (∼50% of the width of the Hermean tail). The downtail location of the neutral line is not self‐consistent or in agreement with previous (independent) studies unless dissipation terms are included planetward of the reconnection site; potential physical explanations are discussed. In the future the model could be adapted to other environments, for example, the dayside magnetopause or other planetary magnetotails. Key Points: Monte Carlo model allows the estimation of X‐line location and reconnection frequency given sampling with a single spacecraftMercury's magnetotail reconnection site is consistent with a center offset (0.37‐1.02+1.21RM) dawnward of midnightMercury's downtail X‐line location is only self‐consistent if dissipation terms are included planetward of the X‐line [ABSTRACT FROM AUTHOR]