Atmospheric escape is always a key issue in understanding the evolution of terrestrial planets. A major science objective of Mercury research is to understand the linkage between solar irradiance, solar wind and the transfer of neutral and ionized Sodium and other heavy species into the exosphere and magnetosphere. There are major discrepancies between Mercury’s extreme ultraviolet radiation and in situ plasma composition measurements concerning the mass densities of neutral and ion species in Mercury’s magnetosphere. James et al.  identifiy and analyze field line resonant ultra-low frequency waves, providing a new measurement of total ion mass density throughout the inner, closed field line region of the magnetosphere. This information opens a new window on this major planetary and magnetospheric science question.
Citation: James, M. K., Imber, S. M., Yeoman, T. K., & Bunce, E. J. . Field line resonance in the Hermean magnetosphere: Structure and implications for plasma distribution. Journal of Geophysical Research: Space Physics, 124. https://doi.org/10.1029/2018JA025920
—Yuming Wang, Editor, JGR: Space Physics