View of GJ 436 b exosphere (gray dots) from the perpendicular to the orbital plane, 3.5 h after the optical transit. The white dashed line shows the LOS toward Earth. Arrows display the velocity field of the hydrogen atoms with respect to the star, colored as a function of the time they escaped the atmosphere (counted from the center of the optical transit). In the reduced gravity field from the star, particles move beyond the orbit of the planet. However, radiation pressure does not overcome stellar gravity, and particles are still deviated from the tangent to the orbit at the time of their escape (solid colored lines). Because radiation pressure is velocity-dependent, the particles do not stay on Keplerian orbits. To better illustrate the effect of radiative braking, this simulation was performed with a low ionization rate artificially lengthening the exospheric tail.