Electrostatic solitary wave (ESW)—a Debye-scale structure in space plasmas—was believed to accelerate electrons. However, such a belief is still unverified in spacecraft observations, because the ESW usually moves fast in spacecraft frame and its interior has never been directly explored. Here, we report the first measurements of an ESW’s interior, by the Magnetospheric Multiscale mission located in a magnetotail reconnection jet. We find that this ESW has a parallel scale of $5{\lambda }_{\mathrm{De}}$ (Debye length), a superslow speed ($99\mathrm{km}/\mathrm{s}$) in spacecraft frame, a longtime duration (250 ms), and a potential drop $e{\phi }_0/k{T}_e\sim 5\%$. Inside the ESW, surprisingly, there is no electron acceleration, no clear change of electron distribution functions, but there exist strong electrostatic electron cyclotron waves. Our observations challenge the conventional belief that ESWs are efficient at particle acceleration.

On 5 May 2017, MMS observed a crater‐type flux rope on the dawnside tailward magnetopause with fluctuations. The boundary‐normal analysis shows that the fluctuations can be attributed to nonlinear Kelvin‐Helmholtz (KH) waves. Reconnection signatures such as flow reversals and Joule dissipation were identified at the leading and trailing edges of the flux rope. In particular, strong northward electron jets observed at the trailing edge indicated midlatitude reconnection associated with the 3‐D structure of the KH vortex. The scale size of the flux rope, together with reconnection signatures, strongly supports the interpretation that the flux rope was generated locally by KH vortex‐induced reconnection. The center of the flux rope also displayed signatures of guide‐field reconnection (out‐of‐plane electron jets, parallel electron heating, and Joule dissipation). These signatures indicate that an interface between two interlinked flux tubes was undergoing interaction, causing a local magnetic depression, resulting in an M‐shaped crater flux rope, as supported by reconstruction.

Electron‐scale magnetic holes (ESMHs) have been widely observed in astrophysical and space plasmas, while their generations, evolutions, and three‐dimensional topologies are still unclear. Here we report two ESMH events detected by the Magnetospheric Multiscale spacecraft in the solar wind and the magnetosheath, respectively. The divergence analysis for the magnetic field indicates that ESMHs have nonlinear field topologies. Then a recently developed reconstruction method, based on the second‐order Taylor expansion, is applied to such ESMHs. Eventually, the first three‐dimensional topologies of ESMHs are obtained. The reconstructed results show that the ESMHs may have complex cross‐section shapes (e.g., saddle‐like shapes) and comparable extension lengths in the parallel and perpendicular directions to the magnetic field, which are inconsistent with the cylinder simplifications for a magnetic hole in previous studies. This work could improve our understandings for the geometric properties and thereby the generations and evolutions of ESMHs.

Magnetic holes (MHs)—depressions in magnetic field strength—have been reported around dipolarization fronts (DFs), but their generation and dynamics remain elusive owing to the limited capacity of previous spacecraft measurements. Taking advantage of magentospheric multiscale mission high‐resolution data, here we present the first observational evidence for MH generation by electron mirror instability behind a DF. The MH is sustained by an electron flow vortex at sub‐proton scale and primarily drifting downward. Instability analysis shows that local condition is unstable to electron mirror instability, suggesting that the MH is electron mirror mode. The MH contains strong field‐aligned currents which may contribute to the magnetosphere‐ionosphere coupling. The MH also hosts oscillatory energy conversion with energy loads dominant (integral of E·J is positive), suggesting that it can be efficient in transferring electromagnetic energy into particle energy. Sub‐ion‐scale dissipation of the magnetic field is coupled with electron‐scale whistlers and Debye‐scale solitary waves, indicating cross‐scale coupling therein.

Electron pitch‐angle distributions, including isotropy, pancake, cigar, butterfly, and recently discovered rolling‐pin distributions, are crucial to understanding electron dynamics in the magnetotail. However, occurrence rates of these distributions remain unclear. Here, for the first time, we reveal the occurrence rates of these distributions in the magnetotail by using Cluster data during 2001–2009, with special focus on the newly reported rolling‐pin distribution. We find that percentages of these distributions are 44.7% (isotropy), 31.3% (pancake), 17.5% (cigar), 4.9% (rolling‐pin), and 1.6% (butterfly), respectively. We find that in the XY_GSM plane, occurrence rates of these PADs peak near: [X_GSM ≈ −11 R_E, Y_GSM ≈ −5 R_E] (isotropy), [X_GSM ≈ −15 R_E, Y_GSM ≈ −11 R_E] (pancake), [X_GSM ≈ −11 R_E, Y_GSM ≈ −5 R_E] (cigar), [X_GSM ≈ −11 R_E, Y_GSM ≈ −3 R_E] (rolling‐pin), and [X_GSM ≈ −11 R_E, Y_GSM ≈ −4 R_E] (butterfly), respectively; and along the r direction, where r is the distance to the center of the Earth in the XY_GSM plane, their occurrence rates peak near: −18 R_E < r < −12 R_E (isotropy), −20 R_E < r < −12 R_E (pancake), −16 R_E < r < −10 R_E (cigar), r ≈ −13 R_E (rolling‐pin), and −14 R_E < r < −10 R_E (butterfly), respectively. Such rates indicate that the rolling‐pin and cigar distributions have similar occurrence rates, supporting previous studies suggesting that rolling‐pin distributions arise from cigar distributions. All distributions have maximum occurrences near the equator but at different subregions. We cannot find any statistical correlation between magnetic structures and the rolling‐pin distributions, different from previous studies suggesting a close connection between them.

Betatron cooling, a plasma process losing particle energy in the perpendicular direction but reserving particle energy in the field‐aligned direction, is a consequence of magnetic depression under the conservation of magnetic moment. Such process has been widely studied in the Earth's magnetosphere but has never been reported in other planetary environment. Here, by utilizing the Mars Atmosphere and Volatile EvolutioN (MAVEN) measurements, we report two events of betatron cooling in the Martian magnetotail. In one of the events, betatron cooling occurs in the suprathermal and energetic ranges of electrons, whereas in the other event, it occurs in the thermal‐energy range. We quantitatively reproduce these two processes by using an analytical model. Gratifyingly, the cooling factor derived from the analytical model agrees well with the observation of magnetic depression. These results, for the first time demonstrating the betatron‐cooling effect beyond the Earth, are useful to understand the electron dynamics in the planetary magnetosphere.