Search

International audience; Soft X-rays are emitted when highly charged solar wind particles like O7+ and O8+ exchange electrons with neutral hydrogens. This process is called solar wind charge exchange (SWCX). The Earth's magnetosheath and cusps are expected to emit strong SWCX emissions due to high abundances of both solar wind particles and exospheric hydrogen atoms in these regions. The Solar wind - Magnetosphere - Ionosphere Link Explorer (SMILE) mission, selected by ESA and China with launch in 2023, will image the Earth's dayside system in soft X-rays. To support the SMILE mission, we conduct a statistical study on the near-Earth SWCX signals using the XMM-Newton astrophysics observations. XMM-Newton is a European X-ray telescope launched in 1999 and has observed cosmic X-ray sources for nearly 18 years. At times, its line-of-sight passes the dayside magnetosheath, and the telescope detects near-Earth SWCX emissions in addition to X-ray light sources like stars and galaxies, diffuse astronomical X-ray backgrounds like interstellar and intergalactic clouds, diffuse heliospheric SWCX signals, and particle backgrounds from the telescope's own glow. We introduce how to extract near-Earth SWCX signals from the XMM-Newton's raw observation data. Then, we investigate the relation of near-Earth X-ray emissions to the solar irradiance, solar wind flux, and abundances of X-ray source particles in solar wind.

Ganymede is a unique object: it is the biggest moon of our solar system, and the only satellite which has its own intrinsic magnetic field leading to the formation of a small magnetosphere. The magnetosphere of Ganymede being embedded in the Jovian magnetosphere, the environment of the Galilean moon presents the only known case of interaction between two magnetospheres (Kivelson et al. 1996). This peculiar interaction has been investigated by means of a 3D parallel multi-species hybrid model based on a CAM-CL algorithm (Mathews et al. 1994). This generic model has been largely used for other magnetized or unmagnetized bodies such as Mars (Modolo et al. 2005; 2006 and 2012), Titan (Modolo et al. 2007, Modolo and Chauteur 2008) or Mercury (Richer et al. 2012). IIn this formalism, ions have a kinetic description whereas electrons are considered as an inertialess fluid which ensure the neutrality of the plasma and contribute to the total current and electronic pressure. Maxwell's equations are solved to compute the temporal evolution of electromagnetic field. The hybrid simulation describes the dynamics of the magnetospheric plasma, composed of O+ and H+ ions, and Ganymede's ionospheric plasma (W+, H2+, H+). Similarly to Paty and Winglee (2004), a density profile with a scale height of 125km of the ionospheric plasma is loaded and feeded during the simulation. Charge exchange leading to H2+ and H+ are also computed. To represent Ganymede's magnetosphere a magnetic dipole is implemented at initialization with dipolar moments values taken from Kivelson et al, 2002. This dipole is progressively distorted and lead to the formal of the mini-magnetopshere. Simulation results also emphasize the presence of Alfvén wings and are in good agreement with other simulation results (Jia et al, 2008, Paty et al, 2008). Hybrid simulations are performed on a uniform cartesian grid with a spatial resolution of about 200 km. Simulations results are presented and compared to magnetometer and particle observations obtained during G1 and G2 Galileo flybys.

International audience; Recent observations and simulations showed the importance of the upper atmosphere/ionosphere in the escape processes at Mars. The solar wind interacts with the Martian ionosphere leading to an ionospheric outflow into the Martian induced magnetosphere. One of the goals of the Heliosares project is to simulate this ionospheric outflow, by coupling a GCM-Ionospheric model, an exospheric model and a Mars-Solar wind interaction model for different solar conditions. In this presentation, we will present the 3D dynamical ionospheric core implemented in the Martian GCM model developed at LMD. This core solves the ions and electrons dynamics equations including the interaction with the neutral atmosphere and taking into account the effect of polarization electric field due to electronic pressure. The numerical approach used to solve the dynamics equations and the first results of this model will be presented as well as the future improvements.

International audience; Discrete auroral arcs regularly display small- and meso-scale distortions that can appear suddenly and move with speeds that are not related to plasma speeds in the ionosphere but rather represent properties of the acceleration processes in the magnetosphere. The temporal and spatial structure of each small-scale structure is thus evidence for its distinct dynamic role in the interaction between the hot magnetospheric and the cold, dense ionospheric plasmas. We analyzed passes of Reimei and FAST over the network of THEMIS Ground-Based Observatories (GBO) with all-sky cameras to combine small- and medium-scale auroral imaging with in-situ measurements of the precipitating particles in order to determine the properties and characteristics of auroral arcs and embedded small-scale structures. The THEMIS or Cluster spacecraft provided additional measurements of magnetospheric plasma and the GBO magnetometers allowed for the determination of ionospheric currents and their dynamic changes. The combination of in-situ and remotely determined auroral arc properties allowed for the complete characterization of a substorm breakup arc and embedded small-scale structures. We find consistency between theoretical expectations and observed values for arc and fold speeds and dimensions. The leading edge of the breakup arc with Alfvenic accelerated electrons exhibits the fastest fold speeds while the wider inverted-V arc shows less structure and internal speeds. Twin vortex shear flows observed by two of the THEMIS spacecraft are related to the poleward expansion of the breakup arc, the development of the substorm current wedge, and the appearance of a strong upward/downward current system. The scale size and motion of the small-scale structures signifies the dynamics of the magnetospheric plasma and the acceleration processes responsible for their generation.