Ludivine Leclercq

Mars-solar wind interaction: LatHyS, an improved parallel 3-D multispecies hybrid model

In order to better represent Mars-Solar wind interaction, we present an unprecedented model achieving spatial resolution down to 50 km, a so far unexplored resolution for global kinetic models of the Martian ionized environment. Such resolution approaches the ionospheric plasma scale height. In practice, the model is derived from a first version described in Modolo et al. [2005]. An important effort of parallelization has been conducted and is presented here. A better description of the ionosphere was also implemented including ionospheric chemistry, electrical conductivities and a drag force modelling the ion-neutral collisions in the ionosphere. This new version of the code, named LatHyS (Latmos Hybrid Simulation), is here used to characterize the impact of various spatial resolutions on simulation results. In addition, and following a global model challenge effort [Brain et al., 2010], we present the results of simulation run for three cases which allows addressing the effect of the supra-thermal corona and of the solar EUV activity on the magnetospheric plasma boundaries and on the global escape. Simulation results showed that global patterns are relatively similar for the different spatial resolution runs but finest grid runs provide a better representation of the ionosphere and display more details of the planetary plasma dynamic. Simulation results suggest that a significant fraction of escaping O+ ions is originated from below 1200 km altitude.

On the orbital variability of Ganymede's atmosphere

Ganymedes atmosphere is produced by radiative interactions with its surface, sourced by the Sun and the Jovian plasma. The sputtered and thermally desorbed molecules are tracked in our Exospheric Global Model (EGM), a 3-D parallelized collisional model. This program was developed to reconstruct the formation of the upper atmosphere/exosphere of planetary bodies interacting with solar photon flux and magnetospheric and/or the solar wind plasmas. Here, we describe the spatial distribution of the H2O and O2 components of Ganymedes atmosphere, and their temporal variability along Ganymedes rotation around Jupiter. In particular, we show that Ganymedes O2 atmosphere is characterized by time scales of the order of Ganymedes rotational period with Jupiters gravity being a significant driver of the spatial distribution of the heaviest exospheric components. Both the sourcing and the Jovian gravity are needed to explain some of the characteristics of the observed aurora emissions. As an example, the O2 exosphere should peak at the equator with systematic maximum at the dusk equator terminator. The sputtering rate of the H2O exosphere should be maximum on the leading hemisphere because of the shape of the open/close field lines boundary and displays some significant variability with longitude.