**4. Conditions applicable to other planets**

The main output of these concepts is that the position of the vortex structures along the Venus wake and their width measured along the VEX trajectory vary along the solar cycle thus implying a continuous displacement of the region where they apply. Similar conditions should also be applicable along the plasma wake of other planets and satellites within the solar system and may as well reach those suitable to exo-planets impacted by stellar winds.

Throughout the solar system the most likely candidates are Venus and Mars which do not have a strong intrinsic magnetic field that deflects the solar wind before it reaches their upper atmosphere/ionosphere. While plasma vortices have been inferred from measurements made along the flanks of the earth's magnetosphere [11–13] changes in their position are not expected to produce local variations as notable as those measured in the Venus wake. On the other hand observations of vortex oscillations have been reported from measurements conducted with the MAVEN spacecraft by the solar wind Mars ionosphere boundary [14] and it is possible that they produce vortex structures similar to those detected in the Venus wake. Comparable conditions may also occur around the Titan ionosphere when it is subject to the solar wind flow and/or to plasma motion within Saturn's magnetosphere when it moves across it. The dynamic pressure of the plasma pressure that reaches Titan is very different in both cases and thus

should produce vortex structures that are situated at different locations along its plasma wake. External to the solar system it is also possible that exo-planets moving within stellar systems will be subject to stellar winds that do not have the same intensity and thus arrive from different directions. In such cases vortex structures may be present at varying distances along their wake and be located at varying distances downstream from exo-planets. Stellar winds with different flow intensity, plasma temperature, and stellar irradiance will in addition influence the position and configuration of vortex structures in an exo-planet wake. A notable effect is the subsonic to supersonic speed change that depends on the coronal temperature of a star as implied from the solution of the fluid dynamic Parker equations of solar wind acceleration [15]. Equally important is the requirement that fluid dynamic vortex structures will be influenced by a planetary magnetic field as it is the case along the earth's wake.
