Thin current sheets in planetary magnetotails: from ion to sub-ion kinetic scales
Abstract
Current sheets (CSs) play a crucial role in the storage and conversion of magnetic energy in planetary magnetotails. In situ spacecraft observations have revealed the formation of the CSs in very different planetary magnetospheres as well as in the solar wind. Multispacecraft observations in the terrestrial magnetotail reported that the CS thinning and intensification can result in formation of multiscale current structure in which a very thin and intense current layer at the center of the CS is embedded into a thicker sheet. To describe such CSs fully kinetic description taking into account all peculiarities of non-adiabatic particle dynamics is required. Kinetic description brings kinetic scales to the CS models. Ion scales are controlled by thermal ion Larmor radius, while scales of sub-ion embedded CS are controlled by the topology of magnetic field lines until the electron motion is magnetized by a small component of the magnetic field existing in a very center of the CS. In the presence of heavy ions the proton layer could be, in its turn, embedded into a thicker and weaker sheet generated by heavy ions. Such multiscale current structures have been observed in a large number of different experiments in the terrestrial magnetosphere. Recent high resolution magnetic field measurements from MAVEN spacecraft indicate on their presence in the cross-tail CS of Mars. We revealed that the typical half thickness of the embedded Super Thin Current Sheet (STCSs) observed at the center of the CS is much less than the gyroradius of thermal protons. The formation of STCS does not depend on ion composition, but it is controlled by the small value of the normal component of the magnetic field at the neutral plane. Our analysis showed that there is a good agreement between the spatial scaling of multiscale CSs observed in Martian magnetotail and the CS scaling obtained from the quasi-adiabatic model of thin anisotropic CS, if the plasma characteristics in Martian CSs are used as input parameters. Thus, in spite of the significant differences in the CS formation, ion composition, and plasma characteristics in the Earth's and Martian magnetotails, similar kinetic features are observed in the CS structures in the magnetotails of both planets. This phenomenon can be explained by the universal principles of nature. The CS once has been formed, then it should be self-consistently supported by the internal coupling of the total current carried by particles in the CS and its magnetic configuration, and as soon as the system achieved the quasi-equilibrium state, it "forgets" the mechanisms of its formation, and its following existence is ruled by the general principles of plasma kinetic described by Vlasov-Maxwell equations. This work is supported by VolkswagenStiftung Foundation (grant #97 742)
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1080G