Solar Wind and planetary magnetospheres
Résumé
Solar Wind interacts with solar system objects by exchanging momentum and energy. This transfer is particularly effective in the case of weakly magnetized bodies (Mars, Venus and comets) and small magnetosphere (Mercury).
This interaction contributes to the erosion of the gaseous envelop and to the atmospheric dynamic and has therefore an important consequence on the atmospheric evolution of these objects. The electromagnetic coupling with these neutral environments takes place through ionization processes: ionization by solar photons, electron impact ionization (incident plasma electrons ionize the upper atmosphere), and charge exchange between ionized and neutral particles producing a cold ion and a fast neutral.
At Mars, as the solar wind flow approaches the ionospheric region, more and more of ions originating from the planet are incorporated. This mass loading becomes more important as we approach the object, contributes to the loss of momentum of the flow, and leads to a pile-up and a twist of magnetic field lines around the object, creating an induced magnetosphere. Meanwhile, Mercury has an intrinsic magnetic field that forms a magnetosphere that is to say, a region governed by the ''planetary'' magnetic field and confined by the Solar Wind and IMF. The magnetosphere is also populated by ions with a planetary origin.
The main structures of the solar wind plasma interaction with Mars and Mercury can be usually described using a steady state picture; however time-dependent effects play important roles. In the last couple of years we try to address the response of weakly magnetized bodies and small magnetospheres to different time-dependent drivers. Responses of transient events, such IMF rotation or Solar Wind dynamic pressure variation, to induced and intrinsic magnetospheres are compared by means of sophisticated 3D simulations