Stellar winds and planetary bodies simulations: Lunar type interaction in super-Alfvénic and sub-Alfvénic flows

• Moon's plasma interaction has been studied using hybrid simulations.
• Upstream velocity is modified from super-Alfvénic to sub-Alfvénic regime.
• We establish a picture using plasma waves triggered at the surface of the obstacle.
• We notice new polarization currents driven by the wave structures.
• Decreasing the upstream speed switches the structures from horizontal to vertical.

Exoplanets are a place of numerous new effects in plasma physics and raise interest in extra-solar physics. Mainly specific cases of plasma interaction between planets, moons and the solar wind have been studied up to now, using data from observations within our solar system. A systematic description of the plasma interactions with respect to the properties of the stellar wind has not been made yet. In order to begin a systematization of the interactions, we study the lunar type plasma interaction by means of the A.I.K.E.F. simulation code, based on the hybrid model. By numerical derivation of MHD wave mode propagation, we show that the lunar wake expansion is governed by the MHD modes. Furthermore, the wake structure can be described by analyzing the different types of currents flowing around the lunar wake and assigning each current to the modes triggered by the obstacle. We show that most of the currents present in the lunar type interaction are a diamagnetic or a polarization current. This method has been also applied for results concerning the evolution of the lunar plasma structure by modifying the upstream velocity, with a transition from a super-Alfénic velocity to a sub-Alfvénic regime. The stellar wind transition study shows that the current switches from a horizontal structure where the current is mostly concentrated in the equatorial plane to a vertical structure where the current is mostly distributed along the magnetic field lines.