Search

Abstract: The influence of cometary jets on the solar wind interaction is studied with a 3D hybrid simulation. Anisotropic outgassing patterns were until recently not considered in cometary simulations, despite strong anisotropies found at observations. Comet 67P Churyumov–Gerasimenko, the target of the ROSETTA mission, was chosen as a case study for a simulation series. The cometary outgassing at 2.7AU is modeled to originate from a single sun-facing jet with different levels of collimation, from isotropy to extremely thin jets. As no bow shock is present at this distance, solar wind patterns resulting from the anisotropic outgassing become more apparent. We find narrower jets to increase the standoff distance of the plasma interaction structures. Also, the Mach cone is wider and stronger for certain jet profiles. The magnetic field remains unable to propagate through the coma, resulting in strong draping patterns for narrow jets due to the increased standoff distance. [Copyright &y& Elsevier]

Abstract: The spacecraft P1 of the new ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon''s Interaction with the Sun) mission passed the lunar wake for the first time on February 13, 2010. We present magnetic field and plasma data of this event and results of 3D hybrid simulations. As the solar wind magnetic field was highly dynamic during the passage, a simulation with stationary solar wind input cannot distinguish whether distortions were caused by these solar wind variations or by the lunar wake; therefore, a dynamic real-time simulation of the flyby has been performed. The input values of this simulation are taken from NASA OMNI data and adapted to the P1 data, resulting in a good agreement between simulation and measurements. Combined with the stationary simulation showing non-transient lunar wake structures, a separation of solar wind and wake effects is achieved. An anisotropy in the magnitude of the plasma bulk flow velocity caused by a non-vanishing magnetic field component parallel to the solar wind flow and perturbations created by counterstreaming ions in the lunar wake are observed in data and simulations. The simulations help to interpret the data granting us the opportunity to examine the entire lunar plasma environment and, thus, extending the possibilities of measurements alone: A comparison of a simulation cross section to theoretical predictions of MHD wave propagation shows that all three basic MHD modes are present in the lunar wake and that their expansion governs the lunar wake refilling process. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]