Our planet is distinguished by the presence of an atmosphere and a magnetic field, both of which significantly affect its interaction with the interplanetary environment. Understanding this interaction, which is different from that of all the other planets, is a key piece of the puzzle describing the evolution and degree of habitability of our environment.
The near-Earth atmosphere serves to absorb most of the harmful photon radiation from the Sun. The outer atmosphere incorporates a conducting medium (the ionosphere) that, in conjunction with the Earth's magnetosphere, responds sensitively to variations in the solar wind, which are manifested by large-scale current systems, plasma convection, and the acceleration, trapping, and precipitation of energetic charged particles. Just as understanding the lower boundary interactions of the planet surface with the atmosphere is important, so, too, is our understanding of the interactions at the outer boundary. The outer boundary is extended in altitude, encompassing the ionosphere and thermosphere at its lower edge and the magnetosphere and magnetosheath at its outer edge. Plasma is exchanged between these two regions, and the lower regions of the boundary act as an electrical conductor providing the closure for currents generated in the magnetosphere and magnetosheath. The temporal and spatial scales for these electrical and plasma coupling processes are poorly defined and yet they represent one of the most significant processes distinguishing our planet from the others.
The Global Electrodynamics mission is designed to advance our understandingof these coupling processes by addressing the following questions: 1) How is the electrical connection between the magnetosphere and the interplanetary environment affected by ionospheric conductivity? 2) What are the spatial and temporal scales over which the ionosphere and thermosphere dynamically respond to magnetospheric inputs? and 3) How do plasma flows between the ionosphere and magnetosphere affect the dynamics of the regions? The mission will place into polar orbits multiple satellites, instrumented for both remote sensing and in-situ measurement, to diagnose the dynamics and composition of the ionosphere, magnetosphere, and thermosphere. By appropriately phasing the mission to ensure that data describing the variability of the interplanetary environment are simultaneously available, we will identify the temporal and spatial scales of interest and determine the time lags that connect processes in the magnetosphere with ionospheric responses and processes in the ionosphere with magnetospheric responses.