The dispersion of shock is universal in various media, and in plasmas, standing whistler waves represent the dispersion of collisionless shocks. However, at present, our understanding of the plasma behavior and electric field properties within these waves remains limited. Using conjoint THEMIS and Magnetospheric Multiscale (MMS) observations, we report the first observation of standing whistler wave upstream of a fast shock in Earth’s magnetosheath resulting from the interaction between a solar wind tangential discontinuity and the bow shock. High-resolution MMS measurements provide unprecedented insights into these waves, characterizing their circular polarization, near-parallel propagation to the shock normal, and fixed phase relative to the shock ramp. Moreover, generated ion acoustic waves and wave‒particle interactions are observed in these waves. These findings highlight that the magnetosheath is a compelling region for investigating standing whistler wave properties.

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.

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.

The planetary magnetic fields in the solar system deflect/reflect solar wind at bow shocks in front of their magnetospheres, protecting the planets from direct solar wind bombardment. Indirect evidences suggest that the sporadic magnetic anomalies on the Moon, i.e., the small-scale magnetic fields, do the same, protecting the lunar surface below and even modifying the chemical/optical properties there. It is, however, still unclear how these anomalies interact with solar wind because of lack of in-situ observations. Two key remotely-sensed symptoms, i.e., the lunar reflected ions and the associated ~1Hz waves, are organized in a particular coordinate system here to diagnose the solar wind interaction. We show that particles are reflected around the specular direction above the lunar surface, hinting an electric-field effect in the reflection, and that whistler wings form, suggesting a distinct solar wind interaction scenario to that of a giant planetary field.

A quick and effective technique is developed to diagnose the geomagnetic dipole field based on an unstrained single circular current loop model. In comparsion with previous studies, this technique is able to separate and solve the loop parameters successively. With this technique, one can search the optimum full loop parameters quickly, including the location of loop center, the loop orientation, the loop radius, and the electric current carried by the loop, which can roughly indicate the locations, sizes, orientations of the interior current sources. The technique tests and applications demonstrate that this technique is effective and applicable. This technique could be applied widely in the fields of geomagnetism, planetary magnetism and palaeomagnetism. The further applications and constrains are discussed and cautioned.