Previous studies suggested that Mercury’s terrestrial-like magnetosphere could possess Earth-like field-aligned currents (FACs) despite having no ionosphere. However, due to the limited coverage of spacecraft observations, our knowledge about Mercury’s FACs is scarce. Here, to survey the establishment and global pattern of Mercury’s FACs, we used Amitis, a hybrid-kinetic plasma model, to simulate the response of Mercury’s FACs to different interior conductivity profiles and various orientations of the upstream interplanetary magnetic field (IMF). We find that the planet with a conductive interior favors the establishment of FACs, and that IMF orientation controls the pattern of FACs in a similar manner as it does on Earth. But the response of R2-like FACs to IMF orientation differs, thus we cannot simply regard Mercury’s FACs as a scaled-down version of Earth’s. Comparison between our simulations and the previous data analysis suggests that the effective interior conductance to close Mercury’s FACs is ~2.4-3.4 S.

This paper reports on the standing whistler waves upstream of Mercury’s quasi-perpendicular bow shock. Using MESSENGER’s magnetometer data, 36 wave events were identified during interplanetary coronal mass ejections (ICMEs). These elliptic or circular polarized waves were characterized by: (1) a constant phase with respect to the shock, (2) propagation along the normal direction to the shock surface, and (3) rapid damping over a few wave periods. We inferred the speed of Mercury’s bow shock as ~31 km/s and a shock width of 1.76 ion inertial length. These events were observed in 20% of the MESSENGER orbits during ICMEs. We conclude that standing whistler wave generations at Mercury are generic to ICME impacts and the low Alfvén Mach number (MA) collisionless shock, and are not affected by the absolute dimensions of its bow shock. Our results further support the theory that these waves are generated by the current in the shock.

We expand on previous observations of magnetic reconnection in Jupiter’s magnetosphere by constructing a survey of ion-inertial scale plasmoids in the Jovian magnetotail. We developed an automated detection algorithm to identify reversals in the component and performed the minimum variance analysis for each identified plasmoid to characterize its helical structure. The magnetic field observations were complemented by data collected by the Juno Waves instrument, which is used to estimate the total electron density, and the JEDI energetic particle detectors. We identified 87 plasmoids with ‘peak-to-peak’ durations between 10 s and 300 s. 31 plasmoids possessed a core field and were classified as flux-ropes. The other 56 plasmoids had minimum field strength at their centers and were termed O-lines. Out of the 87 plasmoids, 58 had in situ signatures shorter than 60 s, despite the algorithm’s upper limit to be 300 s, suggesting that smaller plasmoids with shorter durations were more likely to be detected by Juno. We estimate the diameter of these plasmoids assuming a circular cross-section and a travel speed equal to the Alfven speed in the surrounding lobes. Using the electron density inferred by Waves, we contend that these plasmoid diameters were within an order of the local ion-inertial length. Our results demonstrate that magnetic reconnection in the Jovian magnetotail occurs at ion scales like in other space environments. We show that ion-scale plasmoids would need to be released every 0.1 s or less to match the canonical 1 ton/s rate of plasma production due to Io.

Reconnection in the magnetotail occurs along so-called X-lines, where magnetic field lines tear and detach from plasma on microscopic spatial scales (comparable to particle gyroradii). In 2017–2020 the Magnetospheric MultiScale (MMS) mission detected X-lines in the magnetotail enabling their investigation on local scales. However, the global structure and evolution of these X-lines, critical for understanding their formation and total energy conversion mechanisms, remained virtually unknown because of the intrinsically local nature of observations and the extreme sparsity of concurrent data. Here we show that mining a multi-mission archive of space magnetometer data collected over the last 25+ years and then fitting a magnetic field representation modeled using flexible basis-functions, faithfully reconstructs the global pattern of X-lines; 24 of the 26 modeled X-lines match ($B_z=0$ isocontours are within $\sim2$ Earth radii or $R_E$) or nearly match ($B_z=2$ nT isocontours are within $\sim2 R_E$) the locations of the MMS encountered reconnection sites.

Mercury has a terrestrial-like magnetosphere which is usually taken as a scaled-down-version of Earth’s magnetosphere with a similar current system. We examine Mercury’s magnetospheric current system based on a survey of Mercury’s magnetic field measured by the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft as well as computer simulations. We show that there is no significant Earth-like ring current flowing westward around Mercury, instead, we find, for the first time, an eastward current encircling the planet near the night side magnetic equator with an altitude of ~500–1000 km. The eastward current is closed with the dayside magnetopause current and could be driven by the gradient of plasma pressure as a diamagnetic current. Thus, Mercury’s magnetosphere is not a scaled-down Earth magnetosphere, but a unique natural space plasma laboratory. Our findings offer fresh insights to analyze data from the BepiColombo mission, which is expected to orbit Mercury in 2025.

Flux ropes are a magnetic field phenomenon characterized by a filament of twisted magnetic field with an axial core and outer helical wraps. They form in the Martian ionosphere via three distinct mechanisms: boundary wave instabilities (BWI), external reconnection (ER) between the interplanetary magnetic field and the crustal anomalies, and internal reconnection (IR) of the crustal anomalies themselves. We have identified 121 magnetic flux ropes from 1900 orbits using plasma and magnetic field measurements measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, and separate flux ropes into categories based on formation mechanism by analyzing electron signatures. We find evidence for flux ropes formed via BWI, ER, and IR mechanisms which comprise 9%, 34%, and 57% of our dataset, respectively. Flux ropes formed via different mechanisms exhibit differences in location and force-free radius, indicating the formation mechanism of a flux rope impacts their influence on the Martian plasma environment.

With Magnetospheric Multiscale Mission (MMS) observation of a magnetic flux rope of ion scale in magnetopause, we apply the single-point method presented by Rong et al., [2013] to study the magnetic field structure of flux rope. The calculated geometric parameters, e.g. axis orientation, helical handedness, current density, curvature radius, and boundaries of flux rope show well consistency with those derived from the multi-point methods. Thus, the single-point method of Rong et al., [2013] is reliable for studying the interior field structure of magnetic flux rope and could be applied widely to single-point spacecraft missions that examine the dynamics of flux rope.