Mean density and velocity structure in the hydrodynamic simulation of the atmosphere of WASP-8 b. The density is depicted by the dashed line and the velocity by the dash-dotted one. The atmospheric layer where the bulk EUV emission is absorbed is marked by a circle. The triangles mark the radii, where the atmosphere becomes collisionless for neutral hydrogen and protons. The arrow marks the sonic point and the plus sign the Roche lobe size. Oscillations are visible in the velocity structure of the lower atmosphere. The hydrodynamic simulation is only valid below the exobase at 3R_pl. This planet hosts a stable and compact thermosphere.