Simulation of Plasma Interaction with Io’s Atmosphere

Abstract

Articles you may be interested inDevelopment of a chemistry model for DSMC simulation of the atmosphere of Io using molecular dynamics AIP Conf. Proc. 1501, 579 (2012) Abstract. One dimensional Direct Simulation Monte Carlo (DSMC) simulations are used to examine the interaction of the jovian plasma torus with Io's sublimation atmosphere. The hot plasma sweeps past Io at ~57 km/s due to the external Jovian magnetic and corotational electric fields and the resultant energetic collisions both heat and dissociate the neutral gas creating an inflated, mixed atmosphere of SO 2 and its daughter products. The vertical structure and composition of the atmosphere is important for understanding Io's mass loading of the plasma torus, electron excited aurora, and Io's global gas dynamics. Our 1D simulations above a fixed location on the surface of Io allows the O + and S + ions to drift down into the domain where they then undergo elastic and charge exchange collisions with the neutral gas. Each electron's position is determined by the motion of a corresponding ion; however, the electrons retain their own velocity components which are then used during elastic, ionization, and excitation collisions with the neutral gas. Charge exchange creates fast neutral O and S atoms. Molecular Dynamic/QuasiClassical Trajectory (MD/QCT) calculations are used to generate total and reaction cross sections for energetic O+SO 2 collisions [1] as well as for O+O 2 collisions. In addition, the model accounts for photo-dissociation assuming the atmosphere is optically thin. Our previous plasma heating model (without chemistry) agrees well with the vertical structure of the current model at lower altitudes where the gas is collisional; however, at high altitudes (>100 km) significant differences among the models appear. The current model's constant E and B fields results in reacceleration of the ions and electrons to a constant E×B drift velocity towards the surface after collisions with the neutral gas and, while the results are an upper limit on the plasma interaction strength, the results indicate that joule heating is significant, causing large changes in the vertical structure of the atmosphere. Plasma heating of, not momentum transfer to, the atmosphere dominates even for radially inward plasma flows resulting in a hot, inflated atmosphere. The scale heights for the various species were found to be a competition between the hydrodynamic scale height based on the gas constant (for the mixture if collisional) and the production rate from dissociation of SO 2 which depends on the local SO 2 density and available plasma energy at that altitude.

DSMC implementation of MD/QCT generated energy distributions for SO2+ O collisions

“…The initial conditions for each case are defined by the relative collision velocity and the SO 2 internal energy. Relative collision velocities of 1,2,4,8,9,10,12,16,22,30,45,60, and 80 km/s were studied. The initial SO 2 internal energies considered were 1.44, 7.20, 28.79, 57.57, and 86.36 kcal/mol.…”

“…26 First, zero-dimensional, time-dependent DSMC simulations were computed to examine the difference between solutions obtained using the new internal energy distributions and those using the commonly used Larsen-Borgnakke (LB) method. Then, an axi-symmetric counter flow of sulfur dioxide out-gassing from a sphere into the hypervelocity wind of a bombarding atomic oxygen atmosphere, a very simplified model of the complex Io planetary phenomenology modeled by Moore et al, [8][9][10][11] and Walker et al 12,13 in full DSMC planetary simulations, is considered to address the importance of the possible use of the new energy distributions.…”

“…Since Io's atmosphere is rarefied, its planetary gas dynamics is modeled using the Direct Simulation Monte Carlo (DSMC) approach. Comprehensive planetary physics modeling through the use of DSMC by Austin et al, 2, 3 Zhang et al, [4][5][6][7] Moore et al, [8][9][10][11] and Walker et al 12,13 has been ongoing to study the complex phenomenology of Io's energetic, but rarefied atmosphere.…”

Analysis of Molecular Dynamics Based Chemistry Models for DSMC Simulation of the Atmosphere of Io

“…The DSMC method is a numerical approach for solving low Knudsen number fluid flows. The Io DSMC studies are ongoing, led by Prof. David Goldstein and in collaboration with the authors, with comprehensive planetary physics modeling through the use of DSMC by Austin et al, 3,4 Zhang et al, [5][6][7][8] Moore et al, [9][10][11][12] and Walker et al 13,14 These DSMC simulations require accurate chemistry modeling for determining collision and reaction cross section data. 15 There is a lack of reliable data for SO 2 dissociation, however, at the higher collision energies found in the Ionian atmosphere.…”