Space above the Earth’s atmosphere is broadly filled with ionized gas, called plasma. Since the density of the space plasma is mostly small enough to neglect the viscosity – that is, any collisions between ionized space plasma particles are basically negligible, the behavior of it is essentially different from neutral viscous fluids such as air and water. In such a collisionless plasma system, the boundary layer between regions with different plasmaproperties plays a central role in transferring energy and controlling the dynamics of the system itself. The goal of this project is to understand how the energy is transferred across the boundary layer in a collisionless plasma. Although a number of past studies have targeted this fundamental and important problem in space science, quantitative aspects of the realistic transfer process are still poorly understood. This is mainly because the energy in a collisionless plasma tends to be transferred over a broad range of spatiotemporal scales from the plasma particle (kinetic) scale to the global scale of the system, which cannot be handled only from laboratory and spacecraft measurements. Recent advances in numerical simulation enable more quantitative estimates of the transfer process, but still suffer from unrealistic assumptions. On these backgrounds, the scientific focus of this project is to quantify the energy transfer process more exactly than previous studies covering all necessary scales by effectively combining state-of-art plasma simulations and in-situ and remote plasma measurements. The uniqueness of this project is to target various types of boundary layers located in the Earth’s magnetosphere (the region controlled by the terrestrial magnetic field), which cover different factors and scales that control the energy transfer process across the boundary layer – that is, the Earth’s magnetosphere acts as a great experimental station to explore the boundary layer physics. Specifically, in this project, a series of large-scale plasma particle simulations of representative boundary layers in the magnetosphere will be performed on one of the world’s largest supercomputers MareNostrum, under realistic simulation conditions obtained from real in-situ observations by recently launched high-resolution MMS (Magnetospheric Multiscale) spacecraft. The simulation results will be compared to the observation data from the MMS spacecraft, existing other in-situ spacecraft as well as ground-based observatories, which permit to treat both the local boundary layer physics and the global coupling of the local processes. Based on the project results, not only a quantitative understanding of the multi-scale boundary layer physics in the magnetosphere, but also a systematic understanding of the boundary layer physics in collisionless plasma will be obtained for the first time. These newly gained understandings will therefore be applicable to many other planetary and astrophysical objects, and will support future space exploration missions.