Colloquium: Electron-astrophysics: the multi-scale impact of kinetic electron physics in space and astrophysical plasmas
Almost all of the visible matter in the Universe is in the plasma state. The smallest characteristic scales, at which electron dynamics determines the plasma behaviour, are the next frontier in space and astrophysical plasma research. The analysis of astrophysical processes at these scales lies at the heart of the research theme of electron-astrophysics. This research theme builds heavily upon the use of in-situ plasma measurements in accessible near-Earth space plasmas to understand the universal and fundamental processes in cosmic plasmas throughout the Universe.
The kinetic behaviour of electrons in space plasmas is - to a much greater extent than the proton behaviour - the result of an interplay between global and local plasma processes. In the case of the solar wind, for example, the global properties of the heliosphere include the interplanetary electrostatic potential, the large-scale interplanetary magnetic field, and the density profile of the plasma. The local plasma processes include collisions, wave-particle interactions, and turbulence. Through this interplay, the electron distribution function develops interesting kinetic features that are observable in situ.
I will discuss the processes that shape the electron distribution in the solar wind, the interaction of electrons with local structures such as compressive waves and magnetic holes, and the impacts of these structures on the global electron transport in the heliosphere. The regulation of the electron heat flux is of particular interest in this context. I will support these results with observations from Solar Orbiter and Parker Solar Probe. I will then review a selection of the outstanding science questions in the field of electron-astrophysics, discuss their importance, and present a roadmap for answering them through existing and novel space-mission concepts.